Initial OSS commit

.editorconfig

@@ -0,0 +1,3 @@
+indent_style = space
+indent_size = 2
+end_of_line = lf

.eslintrc.js

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+module.exports = {
+  root: true,
+  parser: '@typescript-eslint/parser',
+  plugins: ['@typescript-eslint', 'unused-imports'],
+  parserOptions: {
+    project: ['./packages/**/tsconfig.json', './theatre/**/tsconfig.json'],
+  },
+  extends: [],
+  rules: {
+    '@typescript-eslint/await-thenable': 'warn',
+    '@typescript-eslint/no-throw-literal': 'warn',
+    '@typescript-eslint/switch-exhaustiveness-check': 'error',
+    '@typescript-eslint/consistent-type-imports': [
+      'warn',
+      {
+        prefer: 'type-imports',
+      },
+    ],
+    '@typescript-eslint/ban-types': [
+      'error',
+      {
+        extendDefaults: true,
+        types: {
+          any: {
+            message:
+              "Don't use any. Use $FixMe or another alternative listed at defs.d.ts",
+            fixWith: '$FixMe',
+          },
+          '{}': false,
+          object: false,
+        },
+      },
+    ],
+    '@typescript-eslint/no-unused-vars': 'off',
+    'unused-imports/no-unused-imports-ts': 'warn',
+    'no-restricted-imports': [
+      'error',
+      {
+        paths: [
+          {
+            name: 'lodash',
+            message: 'Use lodash-es which is tree-shaking friendly',
+          },
+        ],
+      },
+    ],
+  },
+}

.gitignore

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+**/node_modules
+**/xeno
+/packages/*/dist
+/theatre/*/dist
+*.log
+*.temp
+/.vscode
+/.history
+**/.DS_Store
+*.tsbuildinfo
+.eslintcache
+
+.yarn/*
+# !.yarn/cache
+!.yarn/patches
+!.yarn/plugins
+!.yarn/releases
+!.yarn/sdks
+!.yarn/versions

.husky/.gitignore

@@ -0,0 +1 @@
+_

.husky/pre-commit

@@ -0,0 +1,4 @@
+#!/bin/sh
+. "$(dirname "$0")/_/husky.sh"
+
+yarn lint-staged

.prettierrc

@@ -0,0 +1,8 @@
+{
+  "printWidth": 80,
+  "semi": false,
+  "singleQuote": true,
+  "trailingComma": "all",
+  "bracketSpacing": false,
+  "proseWrap": "always"
+}

.vscode/launch.json

@@ -0,0 +1,10 @@
+{
+  "configurations": [
+    {
+      "type": "pwa-chrome",
+      "name": "Browser",
+      "request": "launch",
+      "url": "https://dev.theatre.local:10022/"
+    }
+  ]
+}

.vscode/settings.json

@@ -0,0 +1,24 @@
+{
+  "typescript.tsdk": "node_modules/typescript/lib",
+  "files.exclude": {
+    "**/node_modules": true,
+    // "**/.yarn": true,
+    "**/.cache": true,
+    "**/.temp": true,
+    "**/.history": true
+  },
+  "search.exclude": {
+    "**/node_modules": true,
+    "**/bower_components": true,
+    "**/*.code-search": true,
+    "**/dist": true
+  },
+  "eslint.workingDirectories": ["./"],
+  "eslint.options": {
+    "rulePaths": ["./devEnv/eslint/rules"],
+    "ignorePath": ".gitignore"
+  },
+  "eslint.run": "onSave",
+  "eslint.lintTask.enable": true,
+  "eslint.lintTask.options": ". --ext ts,tsx --ignore-path=.gitignore --rulesdir ./devEnv/eslint/rules"
+}

.vscode/tasks.json

@@ -0,0 +1,20 @@
+{
+  // See https://go.microsoft.com/fwlink/?LinkId=733558
+  // for the documentation about the tasks.json format
+  "version": "2.0.0",
+  "tasks": [
+    {
+      "type": "npm",
+      "script": "test -- --watch",
+      "group": "test",
+      "problemMatcher": [],
+      "label": "npm: test"
+    },
+    {
+      "label": "TypeScript watch",
+      "type": "shell",
+      "command": "yarn tsc --build --watch ./devEnv/typecheck-all-projects/tsconfig.all.json",
+      "problemMatcher": ["$tsc-watch"]
+    }
+  ]
+}

.yarn/plugins/@yarnpkg/plugin-compat.cjs

@@ -0,0 +1,7 @@
+module.exports = {
+  name: `@yarnpkg/plugin-compat`,
+  factory: (require) => {
+    // dummy implementation to override the built-in version of this plugin
+    return {}
+  },
+}

.yarnrc.yml

@@ -0,0 +1,9 @@
+nodeLinker: node-modules
+
+plugins:
+  - path: .yarn/plugins/@yarnpkg/plugin-compat.cjs
+    spec: "@yarnpkg/plugin-compat"
+  - path: .yarn/plugins/@yarnpkg/plugin-interactive-tools.cjs
+    spec: "@yarnpkg/plugin-interactive-tools"
+
+yarnPath: .yarn/releases/yarn-2.4.1.cjs

LICENSE

@@ -0,0 +1,202 @@
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LICENSE-AGPL-3.0

@@ -0,0 +1,661 @@
+                    GNU AFFERO GENERAL PUBLIC LICENSE
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+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
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+
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+
+  "Additional permissions" are terms that supplement the terms of this
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+
+  All other non-permissive additional terms are considered "further
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+received it, or any part of it, contains a notice stating that it is
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+  If you add terms to a covered work in accord with this section, you
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+  Additional terms, permissive or non-permissive, may be stated in the
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+  You may not propagate or modify a covered work except as expressly
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+  However, if you cease all violation of this License, then your
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+  9. Acceptance Not Required for Having Copies.
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+
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+
+  Nothing in this License shall be construed as excluding or limiting
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+
+  12. No Surrender of Others' Freedom.
+
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+
+  13. Remote Network Interaction; Use with the GNU General Public License.
+
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+Program, your modified version must prominently offer all users
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+
+  Notwithstanding any other provision of this License, you have
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+
+  14. Revised Versions of this License.
+
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+
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+
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+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
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+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
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+to attach them to the start of each source file to most effectively
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+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
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+    it under the terms of the GNU Affero General Public License as published
+    by the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+
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+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
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+specific requirements.
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU AGPL, see
+<https://www.gnu.org/licenses/>.

README.md

@@ -0,0 +1,20 @@
+# Theatre.js
+
+Theatre.js is an animation library for high-fidelity motion graphics. It is designed to help you express detailed animation, enabling you to create intricate movement, and convey nuance.
+
+Theatre can be used both programmatically _and_ visually:
+
+![Video showing a browser window containing three divs falling from the middle of the screen, and bouncing back up, animated with the help of Theatre.js](https://docs.theatrejs.com/public/preview-1.gif)
+
+Theatre works with all rendering stacks. You can use it to animate DOM elements, THREE.js objects, or any kind of JavaScript variable.
+
+## Guide
+
+TODO
+
+## License
+
+Your use of Theatre.js is governed under the Apache License Version 2.0:
+
+* Theatre's core (`@theatre/core`) is released under the Apache License. Same goes for most packages in this repository.
+* The studio (`@theatre/studio`) is released under the AGPL 3.0 License. This is the package that you use to edit your animations, setup your scenes, etc. You only use the studio during design/development. Your project's final bundle only includes `@theatre/core`, so only the Apache License applies.

babel.config.js

@@ -0,0 +1,24 @@
+module.exports = function (api) {
+  const env = api.env()
+
+  const config = {
+    presets: [['@babel/preset-react'], ['@babel/preset-typescript']],
+    babelrcRoots: ['.', './packages/*', './theatre/*'],
+  }
+  if (env === 'test') {
+    config.presets.unshift(['@babel/preset-env', {targets: {node: 'current'}}])
+  } else {
+    if (env === 'development' || env === 'production') {
+      config.plugins.unshift(
+        ['@babel/plugin-proposal-class-properties', {loose: true}],
+        ['@babel/plugin-proposal-optional-chaining'],
+        ['@babel/plugin-proposal-nullish-coalescing-operator'],
+        ['@babel/plugin-proposal-logical-assignment-operators'],
+      )
+    } else {
+      throw Error(`Babel env ` + env + ' is not yet configured.')
+    }
+  }
+
+  return config
+}

devEnv/eslint/rules/no-relative-imports.js

@@ -0,0 +1,131 @@
+const path = require('path')
+const minimatch = require('minimatch')
+
+// @todo find and acknowledge the original source of this (it was a github gist)
+// @todo this rule is clearly ignoring a bunch of files that do have parent
+// relative paths but don't get caught.
+
+const replace = {
+  meta: {
+    type: 'layout',
+    fixable: 'code',
+    schema: [
+      {
+        type: 'object',
+        properties: {
+          ignore: {
+            type: 'array',
+            items: {
+              type: 'string',
+            },
+          },
+          method: {
+            type: 'string',
+            enum: ['all', 'only-parent'],
+          },
+          aliases: {
+            type: 'array',
+            minItems: 1,
+            items: {
+              properties: {
+                name: {
+                  type: 'string',
+                },
+                path: {
+                  type: 'string',
+                },
+              },
+              required: ['name', 'path'],
+              additionalProperties: false,
+            },
+          },
+        },
+        required: ['aliases'],
+        additionalProperties: false,
+      },
+    ],
+    messages: {
+      'can-replace':
+        'Relative import found. Run autofix to replace these relative imports!',
+      'cannot-replace':
+        'Relative import found. No alias has been defined which matches this import path',
+    },
+  },
+  create: (context) => {
+    return {
+      ImportDeclaration: (node) => {
+        const config = getConfiguration(context)
+
+        if (
+          config.ignorePatterns.some((pattern) =>
+            minimatch(context.getFilename(), pattern),
+          )
+        ) {
+          return
+        }
+
+        evaluateImport(node, config, context)
+      },
+    }
+  },
+}
+
+function evaluateImport(node, config, context) {
+  const {
+    source: {value, range, loc},
+  } = node
+  if (value.startsWith('./') && config.replaceMethod === 'only-parent') {
+    return
+  } else if (!value.startsWith('../')) {
+    return
+  }
+
+  let canFix = false
+  const currentFileDirectory = path.dirname(context.getFilename())
+  for (const alias of config.replaceAliases) {
+    const {replaceDir, replaceWith} = alias
+    const fullImportPath = path.resolve(currentFileDirectory, value)
+
+    if (fullImportPath.startsWith(replaceDir)) {
+      canFix = true
+
+      context.report({
+        messageId: 'can-replace',
+        loc,
+        fix: (fixer) =>
+          fixer.replaceTextRange(
+            range,
+            `'${fullImportPath.replace(replaceDir, replaceWith)}'`,
+          ),
+      })
+
+      break
+    }
+  }
+
+  if (!canFix) {
+    context.report({
+      messageId: 'cannot-replace',
+      loc,
+    })
+  }
+}
+
+function getConfiguration(context) {
+  const options = {
+    ignore: [],
+    method: 'only-parent',
+    ...context.options[0],
+  }
+
+  return {
+    ignorePatterns: options.ignore,
+    replaceMethod: options.method,
+    replaceAliases: options.aliases.map((alias) => ({
+      replaceDir: alias.path,
+      replaceWith: alias.name,
+    })),
+  }
+}
+
+module.exports = replace

devEnv/getAliasesFromTSConfig.d.ts

@@ -0,0 +1,2 @@
+export function getAliasesFromTsConfigForWebpack(): Record<string, string>
+export function getAliasesFromTsConfigForJest(): Record<string, string>

devEnv/getAliasesFromTSConfig.js

@@ -0,0 +1,58 @@
+const path = require('path')
+
+const monorepoRoot = path.resolve(__dirname, '../')
+
+function getAliasesFromTsConfigForWebpack() {
+  const tsConfigPaths = require('../tsconfig.base.json').compilerOptions.paths
+
+  const aliases = {}
+
+  for (let [key, value] of Object.entries(tsConfigPaths)) {
+    if (key.match(/\*$/)) {
+      key = key.replace(/\/\*$/, '')
+    } else {
+      key = key + '$'
+    }
+    aliases[key] = path.join(monorepoRoot, value[0].replace(/\/\*$/, ''))
+  }
+
+  return aliases
+}
+
+module.exports.getAliasesFromTsConfigForWebpack = getAliasesFromTsConfigForWebpack
+
+function getAliasesFromTsConfigForESLint() {
+  const tsConfigPaths = require('../tsconfig.base.json').compilerOptions.paths
+
+  const aliases = []
+
+  for (const [key, value] of Object.entries(tsConfigPaths)) {
+    aliases.push({
+      name: key.replace(/\/\*$/, ''),
+      path: value[0].replace(/\/\*$/, ''),
+    })
+  }
+
+  return aliases
+}
+
+module.exports.getAliasesFromTsConfigForESLint = getAliasesFromTsConfigForESLint
+
+function getAliasesFromTsConfigForJest() {
+  const tsConfigPaths = require('../tsconfig.base.json').compilerOptions.paths
+
+  const aliases = {}
+
+  for (let [key, value] of Object.entries(tsConfigPaths)) {
+    if (key.match(/\/\*$/)) {
+      key = key.replace(/\/\*$/, '/(.*)')
+    } else {
+      key = key + '$'
+    }
+    aliases[key] = path.join('<rootDir>', value[0].replace(/\/\*$/, '/$1'))
+  }
+
+  return aliases
+}
+
+module.exports.getAliasesFromTsConfigForJest = getAliasesFromTsConfigForJest

devEnv/typecheck-all-projects/tsconfig.all.json

@@ -0,0 +1,14 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "composite": true,
+    "rootDir": "../.."
+  },
+  "files": [],
+  "references": [
+    {"path": "../../theatre"},
+    {"path": "../../packages/dataverse"},
+    {"path": "../../packages/playground"},
+    {"path": "../../packages/plugin-r3f"}
+  ]
+}

jest.config.js

@@ -0,0 +1,20 @@
+module.exports = {
+  testMatch: [
+    '<rootDir>/packages/*/src/**/*.test.ts',
+    '<rootDir>/theatre/*/src/**/*.test.ts',
+  ],
+  moduleNameMapper: {
+    ...require('./devEnv/getAliasesFromTSConfig').getAliasesFromTsConfigForJest(),
+    '\\.(css)$': 'identity-obj-proxy',
+    'lodash-es/(.*)': 'lodash/$1',
+    'react-use/esm/(.*)': 'react-use/lib/$1',
+    'lodash-es': 'lodash',
+  },
+  setupFiles: ['./theatre/shared/src/setupTestEnv.ts'],
+  automock: false,
+  transform: {
+    '^.+\\.tsx?$': 'esbuild-jest',
+    '^.+\\.js$': 'esbuild-jest',
+  },
+  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node'],
+}

lerna.json

@@ -0,0 +1,6 @@
+{
+  "packages": ["packages/*", "theatre/*"],
+  "version": "independent",
+  "npmClient": "yarn",
+  "useWorkspaces": true
+}

package.json

@@ -0,0 +1,46 @@
+{
+  "name": "theatre-monorepo",
+  "license": "Apache-2.0",
+  "workspaces": [
+    "packages/*",
+    "theatre"
+  ],
+  "scripts": {
+    "typecheck": "tsc --build ./devEnv/typecheck-all-projects/tsconfig.all.json",
+    "test": "jest",
+    "postinstall": "husky install",
+    "lint:all": "eslint . --ext ts,tsx --ignore-path=.gitignore --rulesdir ./devEnv/eslint/rules"
+  },
+  "lint-staged": {
+    "**/*.(t|j)s?(x)": [
+      "eslint --rulesdir ./devEnv/eslint/rules --fix",
+      "prettier --write"
+    ]
+  },
+  "devDependencies": {
+    "@babel/core": "^7.14.3",
+    "@babel/plugin-proposal-class-properties": "^7.13.0",
+    "@babel/plugin-proposal-nullish-coalescing-operator": "^7.14.2",
+    "@babel/plugin-proposal-optional-chaining": "^7.14.2",
+    "@babel/preset-env": "^7.14.4",
+    "@babel/preset-react": "^7.13.13",
+    "@babel/preset-typescript": "^7.13.0",
+    "@typescript-eslint/eslint-plugin": "^4.26.0",
+    "@typescript-eslint/parser": "^4.26.0",
+    "esbuild": "^0.12.5",
+    "esbuild-jest": "^0.5.0",
+    "eslint": "^7.27.0",
+    "eslint-plugin-jsx-a11y": "^6.4.1",
+    "eslint-plugin-react-hooks": "^4.2.0",
+    "eslint-plugin-unused-imports": "^1.1.1",
+    "husky": "^6.0.0",
+    "jest": "^27.0.3",
+    "lerna": "^4.0.0",
+    "lint-staged": "^11.0.0",
+    "prettier": "^2.3.1",
+    "typescript": "^4.3.2"
+  },
+  "dependencies": {
+    "node-gyp": "^8.1.0"
+  }
+}

packages/dataverse/.babelrc.js

@@ -0,0 +1 @@
+module.exports = {}

packages/dataverse/.gitignore

@@ -0,0 +1 @@
+/dist

packages/dataverse/LICENSE

@@ -0,0 +1,203 @@
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+

packages/dataverse/package.json

@@ -0,0 +1,31 @@
+{
+  "name": "@theatre/dataverse",
+  "version": "1.0.0-dev",
+  "license": "Apache-2.0",
+  "author": {
+    "name": "Aria Minaei",
+    "email": "aria@theatrejs.com",
+    "url": "https://github.com/AriaMinaei"
+  },
+  "source": "src/index.ts",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "files": [
+    "dist/**/*"
+  ],
+  "scripts": {
+    "prepack": "yarn run build",
+    "typecheck": "yarn run build",
+    "build": "tsc --build ./tsconfig.json"
+  },
+  "devDependencies": {
+    "@types/jest": "^26.0.23",
+    "@types/lodash-es": "^4.17.4",
+    "@types/node": "^15.6.2",
+    "@types/react": "^17.0.9",
+    "typescript": "^4.3.2"
+  },
+  "dependencies": {
+    "lodash-es": "^4.17.21"
+  }
+}

packages/dataverse/src/Atom.ts

@@ -0,0 +1,241 @@
+import get from 'lodash-es/get'
+import isPlainObject from 'lodash-es/isPlainObject'
+import last from 'lodash-es/last'
+import DerivationFromSource from './derivations/DerivationFromSource'
+import type {IDerivation} from './derivations/IDerivation'
+import {isDerivation} from './derivations/IDerivation'
+import type {Pointer, PointerType} from './pointer'
+import pointer, {getPointerMeta} from './pointer'
+import type {$FixMe, $IntentionalAny} from './types'
+import type {PathBasedReducer} from './utils/PathBasedReducer'
+import updateDeep from './utils/updateDeep'
+
+type Listener = (newVal: unknown) => void
+
+enum ValueTypes {
+  Dict,
+  Array,
+  Other,
+}
+
+export interface IdentityDerivationProvider {
+  readonly $$isIdentityDerivationProvider: true
+  getIdentityDerivation(path: Array<string | number>): IDerivation<unknown>
+}
+
+const getTypeOfValue = (v: unknown): ValueTypes => {
+  if (Array.isArray(v)) return ValueTypes.Array
+  if (isPlainObject(v)) return ValueTypes.Dict
+  return ValueTypes.Other
+}
+
+const getKeyOfValue = (
+  v: unknown,
+  key: string | number,
+  vType: ValueTypes = getTypeOfValue(v),
+): unknown => {
+  if (vType === ValueTypes.Dict && typeof key === 'string') {
+    return (v as $IntentionalAny)[key]
+  } else if (vType === ValueTypes.Array && isValidArrayIndex(key)) {
+    return (v as $IntentionalAny)[key]
+  } else {
+    return undefined
+  }
+}
+
+const isValidArrayIndex = (key: string | number): boolean => {
+  const inNumber = typeof key === 'number' ? key : parseInt(key, 10)
+  return (
+    !isNaN(inNumber) &&
+    inNumber >= 0 &&
+    inNumber < Infinity &&
+    (inNumber | 0) === inNumber
+  )
+}
+
+class Scope {
+  children: Map<string | number, Scope> = new Map()
+  identityChangeListeners: Set<Listener> = new Set()
+  constructor(
+    readonly _parent: undefined | Scope,
+    readonly _path: (string | number)[],
+  ) {}
+
+  addIdentityChangeListener(cb: Listener) {
+    this.identityChangeListeners.add(cb)
+  }
+
+  removeIdentityChangeListener(cb: Listener) {
+    this.identityChangeListeners.delete(cb)
+    this._checkForGC()
+  }
+
+  removeChild(key: string | number) {
+    this.children.delete(key)
+    this._checkForGC()
+  }
+
+  getChild(key: string | number) {
+    return this.children.get(key)
+  }
+
+  getOrCreateChild(key: string | number) {
+    let child = this.children.get(key)
+    if (!child) {
+      child = child = new Scope(this, this._path.concat([key]))
+      this.children.set(key, child)
+    }
+    return child
+  }
+
+  _checkForGC() {
+    if (this.identityChangeListeners.size > 0) return
+    if (this.children.size > 0) return
+
+    if (this._parent) {
+      this._parent.removeChild(last(this._path) as string | number)
+    }
+  }
+}
+
+export default class Atom<State extends {}>
+  implements IdentityDerivationProvider
+{
+  private _currentState: State
+  readonly $$isIdentityDerivationProvider = true
+  private readonly _rootScope: Scope
+  readonly pointer: Pointer<State>
+
+  constructor(initialState: State) {
+    this._currentState = initialState
+    this._rootScope = new Scope(undefined, [])
+    this.pointer = pointer({root: this as $FixMe, path: []})
+  }
+
+  setState(newState: State) {
+    const oldState = this._currentState
+    this._currentState = newState
+
+    this._checkUpdates(this._rootScope, oldState, newState)
+  }
+
+  getState() {
+    return this._currentState
+  }
+
+  getIn(path: (string | number)[]): unknown {
+    return path.length === 0 ? this.getState() : get(this.getState(), path)
+  }
+
+  reduceState: PathBasedReducer<State, State> = (
+    path: $IntentionalAny[],
+    reducer: $IntentionalAny,
+  ) => {
+    const newState = updateDeep(this.getState(), path, reducer)
+    this.setState(newState)
+    return newState
+  }
+
+  setIn(path: $FixMe[], val: $FixMe) {
+    return this.reduceState(path, () => val)
+  }
+
+  private _checkUpdates(scope: Scope, oldState: unknown, newState: unknown) {
+    if (oldState === newState) return
+    scope.identityChangeListeners.forEach((cb) => cb(newState))
+
+    if (scope.children.size === 0) return
+    const oldValueType = getTypeOfValue(oldState)
+    const newValueType = getTypeOfValue(newState)
+
+    if (oldValueType === ValueTypes.Other && oldValueType === newValueType)
+      return
+
+    scope.children.forEach((childScope, childKey) => {
+      const oldChildVal = getKeyOfValue(oldState, childKey, oldValueType)
+      const newChildVal = getKeyOfValue(newState, childKey, newValueType)
+      this._checkUpdates(childScope, oldChildVal, newChildVal)
+    })
+  }
+
+  private _getOrCreateScopeForPath(path: (string | number)[]): Scope {
+    let curScope = this._rootScope
+    for (const pathEl of path) {
+      curScope = curScope.getOrCreateChild(pathEl)
+    }
+    return curScope
+  }
+
+  private _onPathValueChange = (
+    path: (string | number)[],
+    cb: (v: unknown) => void,
+  ) => {
+    const scope = this._getOrCreateScopeForPath(path)
+    scope.identityChangeListeners.add(cb)
+    const untap = () => {
+      scope.identityChangeListeners.delete(cb)
+    }
+    return untap
+  }
+
+  getIdentityDerivation(path: Array<string | number>): IDerivation<unknown> {
+    return new DerivationFromSource<$IntentionalAny>(
+      (listener) => this._onPathValueChange(path, listener),
+      () => this.getIn(path),
+    )
+  }
+}
+
+const identityDerivationWeakMap = new WeakMap<{}, IDerivation<unknown>>()
+
+export const valueDerivation = <P extends PointerType<$IntentionalAny>>(
+  pointer: P,
+): IDerivation<P extends PointerType<infer T> ? T : void> => {
+  const meta = getPointerMeta(pointer)
+
+  let derivation = identityDerivationWeakMap.get(meta)
+  if (!derivation) {
+    const root = meta.root
+    if (!isIdentityChangeProvider(root)) {
+      throw new Error(
+        `Cannot run valueDerivation() on a pointer whose root is not an IdentityChangeProvider`,
+      )
+    }
+    const {path} = meta
+    derivation = root.getIdentityDerivation(path)
+    identityDerivationWeakMap.set(meta, derivation)
+  }
+  return derivation as $IntentionalAny
+}
+
+export function isIdentityChangeProvider(
+  val: unknown,
+): val is IdentityDerivationProvider {
+  return (
+    typeof val === 'object' &&
+    val !== null &&
+    (val as $IntentionalAny)['$$isIdentityDerivationProvider'] === true
+  )
+}
+
+export const val = <P>(
+  pointerOrDerivationOrPlainValue: P,
+): P extends PointerType<infer T>
+  ? T
+  : P extends IDerivation<infer T>
+  ? T
+  : unknown => {
+  if (isPointer(pointerOrDerivationOrPlainValue)) {
+    return valueDerivation(
+      pointerOrDerivationOrPlainValue,
+    ).getValue() as $IntentionalAny
+  } else if (isDerivation(pointerOrDerivationOrPlainValue)) {
+    return pointerOrDerivationOrPlainValue.getValue() as $IntentionalAny
+  } else {
+    return pointerOrDerivationOrPlainValue as $IntentionalAny
+  }
+}
+
+export const isPointer = (p: $IntentionalAny): p is Pointer<unknown> => {
+  return p && p.$pointerMeta ? true : false
+}

packages/dataverse/src/Box.ts

@@ -0,0 +1,34 @@
+import DerivationFromSource from './derivations/DerivationFromSource'
+import type {IDerivation} from './derivations/IDerivation'
+import Emitter from './utils/Emitter'
+export interface IBox<V> {
+  set(v: V): void
+  get(): V
+  derivation: IDerivation<V>
+}
+
+export default class Box<V> implements IBox<V> {
+  private _publicDerivation: IDerivation<V>
+  private _emitter = new Emitter<V>()
+
+  constructor(protected _value: V) {
+    this._publicDerivation = new DerivationFromSource(
+      (listener) => this._emitter.tappable.tap(listener),
+      this.get.bind(this),
+    )
+  }
+
+  set(v: V) {
+    if (v === this._value) return
+    this._value = v
+    this._emitter.emit(v)
+  }
+
+  get() {
+    return this._value
+  }
+
+  get derivation() {
+    return this._publicDerivation
+  }
+}

packages/dataverse/src/Freshener.ts

@@ -0,0 +1,84 @@
+type ICallback = (t: number) => void
+
+export default class Freshener {
+  private _scheduledForThisOrNextTick: Set<ICallback>
+  private _scheduledForNextTick: Set<ICallback>
+  private _timeAtCurrentTick: number
+  private _freshening: boolean = false
+
+  constructor() {
+    this._scheduledForThisOrNextTick = new Set()
+    this._scheduledForNextTick = new Set()
+    this._timeAtCurrentTick = 0
+  }
+
+  /**
+   * Registers for fn to be called either on this freshen or the next freshen.
+   *
+   * If registerSideEffect() is called while Freshener.freshen() is running, the
+   * side effect _will_ be called within the running freshen. If you don't want this
+   * behavior, you can use registerSideEffectForNextTick().
+   *
+   * Note that fn will be added to a Set(). Which means, if you call registerSideEffect(fn)
+   * with the same fn twice in a single freshen, it'll only run once.
+   */
+  onThisOrNextTick(fn: ICallback) {
+    this._scheduledForThisOrNextTick.add(fn)
+  }
+
+  /**
+   * Registers a side effect to be called on the next freshen.
+   *
+   * @see Freshener:onThisOrNextTick()
+   */
+  onNextTick(fn: ICallback) {
+    this._scheduledForNextTick.add(fn)
+  }
+
+  offThisOrNextTick(fn: ICallback) {
+    this._scheduledForThisOrNextTick.delete(fn)
+  }
+
+  offNextTick(fn: ICallback) {
+    this._scheduledForNextTick.delete(fn)
+  }
+
+  get time() {
+    if (this._freshening) {
+      return this._timeAtCurrentTick
+    } else return performance.now()
+  }
+
+  freshen(t: number = performance.now()) {
+    this._freshening = true
+    this._timeAtCurrentTick = t
+    this._scheduledForNextTick.forEach((v) =>
+      this._scheduledForThisOrNextTick.add(v),
+    )
+    this._scheduledForNextTick.clear()
+    this._freshen(0)
+    this._freshening = false
+  }
+
+  private _freshen(iterationNumber: number): void {
+    const time = this.time
+
+    if (iterationNumber > 10) {
+      console.warn('_freshen() recursing for 10 times')
+    }
+
+    if (iterationNumber > 100) {
+      throw new Error(`Maximum recursion limit for _tick()`)
+    }
+
+    const oldSet = this._scheduledForThisOrNextTick
+    this._scheduledForThisOrNextTick = new Set()
+    oldSet.forEach((fn) => {
+      fn(time)
+    })
+
+    if (this._scheduledForThisOrNextTick.size > 0) {
+      return this._freshen(iterationNumber + 1)
+    }
+  }
+}

packages/dataverse/src/PointerProxy.ts

@@ -0,0 +1,34 @@
+import type {IdentityDerivationProvider} from './Atom'
+import type {Pointer} from './pointer';
+import pointer from './pointer'
+import type {IBox} from './Box';
+import Box from './Box'
+import type {$FixMe, $IntentionalAny} from './types'
+import {valueDerivation} from '@theatre/dataverse'
+
+export default class PointerProxy<O extends {}>
+  implements IdentityDerivationProvider
+{
+  readonly $$isIdentityDerivationProvider = true
+  private readonly _currentPointerBox: IBox<Pointer<O>>
+  readonly pointer: Pointer<O>
+
+  constructor(currentPointer: Pointer<O>) {
+    this._currentPointerBox = new Box(currentPointer)
+    this.pointer = pointer({root: this as $FixMe, path: []})
+  }
+
+  setPointer(p: Pointer<O>) {
+    this._currentPointerBox.set(p)
+  }
+
+  getIdentityDerivation(path: Array<string | number>) {
+    return this._currentPointerBox.derivation.flatMap((p) => {
+      const subPointer = path.reduce(
+        (pointerSoFar, pathItem) => (pointerSoFar as $IntentionalAny)[pathItem],
+        p,
+      )
+      return valueDerivation(subPointer)
+    })
+  }
+}

packages/dataverse/src/Ticker.ts

@@ -0,0 +1,84 @@
+type ICallback = (t: number) => void
+
+export default class Ticker {
+  private _scheduledForThisOrNextTick: Set<ICallback>
+  private _scheduledForNextTick: Set<ICallback>
+  private _timeAtCurrentTick: number
+  private _ticking: boolean = false
+
+  constructor() {
+    this._scheduledForThisOrNextTick = new Set()
+    this._scheduledForNextTick = new Set()
+    this._timeAtCurrentTick = 0
+  }
+
+  /**
+   * Registers for fn to be called either on this tick or the next tick.
+   *
+   * If registerSideEffect() is called while Ticker.tick() is running, the
+   * side effect _will_ be called within the running tick. If you don't want this
+   * behavior, you can use registerSideEffectForNextTick().
+   *
+   * Note that fn will be added to a Set(). Which means, if you call registerSideEffect(fn)
+   * with the same fn twice in a single tick, it'll only run once.
+   */
+  onThisOrNextTick(fn: ICallback) {
+    this._scheduledForThisOrNextTick.add(fn)
+  }
+
+  /**
+   * Registers a side effect to be called on the next tick.
+   *
+   * @see Ticker:onThisOrNextTick()
+   */
+  onNextTick(fn: ICallback) {
+    this._scheduledForNextTick.add(fn)
+  }
+
+  offThisOrNextTick(fn: ICallback) {
+    this._scheduledForThisOrNextTick.delete(fn)
+  }
+
+  offNextTick(fn: ICallback) {
+    this._scheduledForNextTick.delete(fn)
+  }
+
+  get time() {
+    if (this._ticking) {
+      return this._timeAtCurrentTick
+    } else return performance.now()
+  }
+
+  tick(t: number = performance.now()) {
+    this._ticking = true
+    this._timeAtCurrentTick = t
+    this._scheduledForNextTick.forEach((v) =>
+      this._scheduledForThisOrNextTick.add(v),
+    )
+    this._scheduledForNextTick.clear()
+    this._tick(0)
+    this._ticking = false
+  }
+
+  private _tick(iterationNumber: number): void {
+    const time = this.time
+
+    if (iterationNumber > 10) {
+      console.warn('_tick() recursing for 10 times')
+    }
+
+    if (iterationNumber > 100) {
+      throw new Error(`Maximum recursion limit for _tick()`)
+    }
+
+    const oldSet = this._scheduledForThisOrNextTick
+    this._scheduledForThisOrNextTick = new Set()
+    oldSet.forEach((fn) => {
+      fn(time)
+    })
+
+    if (this._scheduledForThisOrNextTick.size > 0) {
+      return this._tick(iterationNumber + 1)
+    }
+  }
+}

packages/dataverse/src/atom.typeTest.ts

@@ -0,0 +1,24 @@
+import Atom, {val} from './Atom'
+import {expectType, _any} from './utils/typeTestUtils'
+;() => {
+  const p = new Atom<{foo: string; bar: number; optional?: boolean}>(_any)
+    .pointer
+  expectType<string>(val(p.foo))
+  // @ts-expect-error TypeTest
+  expectType<number>(val(p.foo))
+
+  expectType<number>(val(p.bar))
+  // @ts-expect-error TypeTest
+  expectType<string>(val(p.bar))
+
+  // @ts-expect-error TypeTest
+  expectType<{}>(val(p.nonExistent))
+
+  expectType<undefined | boolean>(val(p.optional))
+  // @ts-expect-error TypeTest
+  expectType<boolean>(val(p.optional))
+  // @ts-expect-error TypeTest
+  expectType<undefined>(val(p.optional))
+  // @ts-expect-error TypeTest
+  expectType<undefined | string>(val(p.optional))
+}

packages/dataverse/src/derivations/AbstractDerivation.ts

@@ -0,0 +1,160 @@
+import type Ticker from '../Ticker'
+import type {$IntentionalAny, VoidFn} from '../types'
+import type Tappable from '../utils/Tappable'
+import DerivationEmitter from './DerivationEmitter'
+import DerivationValuelessEmitter from './DerivationValuelessEmitter'
+import flatMap from './flatMap'
+import type {IDerivation} from './IDerivation'
+import map from './map'
+import {
+  reportResolutionEnd,
+  reportResolutionStart,
+} from './prism/discoveryMechanism'
+
+type IDependent = (msgComingFrom: IDerivation<$IntentionalAny>) => void
+export default abstract class AbstractDerivation<V> implements IDerivation<V> {
+  readonly isDerivation: true = true
+  private _didMarkDependentsAsStale: boolean = false
+  private _isHot: boolean = false
+
+  private _isFresh: boolean = false
+  protected _lastValue: undefined | V = undefined
+
+  protected _dependents: Set<IDependent> = new Set()
+  protected _dependencies: Set<IDerivation<$IntentionalAny>> = new Set()
+
+  protected abstract _recalculate(): V
+  protected abstract _reactToDependencyBecomingStale(
+    which: IDerivation<unknown>,
+  ): void
+
+  constructor() {}
+
+  get isHot(): boolean {
+    return this._isHot
+  }
+
+  protected _addDependency(d: IDerivation<$IntentionalAny>) {
+    if (this._dependencies.has(d)) return
+    this._dependencies.add(d)
+    if (this._isHot) d.addDependent(this._internal_markAsStale)
+  }
+
+  protected _removeDependency(d: IDerivation<$IntentionalAny>) {
+    if (!this._dependencies.has(d)) return
+    this._dependencies.delete(d)
+    if (this._isHot) d.removeDependent(this._internal_markAsStale)
+  }
+
+  changes(ticker: Ticker): Tappable<V> {
+    return new DerivationEmitter(this, ticker).tappable()
+  }
+
+  changesWithoutValues(): Tappable<void> {
+    return new DerivationValuelessEmitter(this).tappable()
+  }
+
+  keepHot() {
+    return this.changesWithoutValues().tap(() => {})
+  }
+
+  tapImmediate(ticker: Ticker, fn: (cb: V) => void): VoidFn {
+    const untap = this.changes(ticker).tap(fn)
+    fn(this.getValue())
+    return untap
+  }
+
+  addDependent(d: IDependent) {
+    const hadDepsBefore = this._dependents.size > 0
+    this._dependents.add(d)
+    const hasDepsNow = this._dependents.size > 0
+    if (hadDepsBefore !== hasDepsNow) {
+      this._reactToNumberOfDependentsChange()
+    }
+  }
+
+  /**
+   * @sealed
+   */
+  removeDependent(d: IDependent) {
+    const hadDepsBefore = this._dependents.size > 0
+    this._dependents.delete(d)
+    const hasDepsNow = this._dependents.size > 0
+    if (hadDepsBefore !== hasDepsNow) {
+      this._reactToNumberOfDependentsChange()
+    }
+  }
+
+  /**
+   * This is meant to be called by subclasses
+   *
+   * @sealed
+   */
+  protected _markAsStale(which: IDerivation<$IntentionalAny>) {
+    this._internal_markAsStale(which)
+  }
+
+  private _internal_markAsStale = (which: IDerivation<$IntentionalAny>) => {
+    this._reactToDependencyBecomingStale(which)
+
+    if (this._didMarkDependentsAsStale) return
+
+    this._didMarkDependentsAsStale = true
+    this._isFresh = false
+
+    this._dependents.forEach((dependent) => {
+      dependent(this)
+    })
+  }
+
+  getValue(): V {
+    reportResolutionStart(this)
+
+    if (!this._isFresh) {
+      const newValue = this._recalculate()
+      this._lastValue = newValue
+      if (this.isHot) {
+        this._isFresh = true
+        this._didMarkDependentsAsStale = false
+      }
+    }
+
+    reportResolutionEnd(this)
+    return this._lastValue!
+  }
+
+  private _reactToNumberOfDependentsChange() {
+    const shouldBecomeHot = this._dependents.size > 0
+
+    if (shouldBecomeHot === this._isHot) return
+
+    this._isHot = shouldBecomeHot
+    this._didMarkDependentsAsStale = false
+    this._isFresh = false
+    if (shouldBecomeHot) {
+      this._dependencies.forEach((d) => {
+        d.addDependent(this._internal_markAsStale)
+      })
+      this._keepHot()
+    } else {
+      this._dependencies.forEach((d) => {
+        d.removeDependent(this._internal_markAsStale)
+      })
+      this._becomeCold()
+    }
+  }
+
+  protected _keepHot() {}
+
+  protected _becomeCold() {}
+
+  map<T>(fn: (v: V) => T): IDerivation<T> {
+    return map(this, fn)
+  }
+
+  flatMap<R>(
+    fn: (v: V) => R,
+  ): IDerivation<R extends IDerivation<infer T> ? T : R> {
+    return flatMap(this, fn)
+  }
+}

packages/dataverse/src/derivations/AbstractDerivation.typeTest.ts

@@ -0,0 +1,36 @@
+import type {$IntentionalAny} from '../types'
+import type {IDerivation} from './IDerivation'
+
+const _any: $IntentionalAny = null
+
+// map
+;() => {
+  const a: IDerivation<string> = _any
+
+  // $ExpectType IDerivation<number>
+  // eslint-disable-next-line unused-imports/no-unused-vars-ts
+  a.map((s: string) => 10)
+
+  // @ts-expect-error
+  // eslint-disable-next-line unused-imports/no-unused-vars-ts
+  a.map((s: number) => 10)
+}
+
+// flatMap()
+/* eslint-disable unused-imports/no-unused-vars-ts */
+;() => {
+  const a: IDerivation<string> = _any
+
+  // okay
+  a.flatMap((s: string) => {})
+
+  // @ts-expect-error TypeTest
+  a.flatMap((s: number) => {})
+
+  // $ExpectType IDerivation<number>
+  a.flatMap((s): IDerivation<number> => _any)
+
+  // $ExpectType IDerivation<number>
+  a.flatMap((s): number => _any)
+}
+/* eslint-enable unused-imports/no-unused-vars-ts */

packages/dataverse/src/derivations/ConstantDerivation.ts

@@ -0,0 +1,17 @@
+import AbstractDerivation from './AbstractDerivation'
+
+export default class ConstantDerivation<V> extends AbstractDerivation<V> {
+  _v: V
+
+  constructor(v: V) {
+    super()
+    this._v = v
+    return this
+  }
+
+  _recalculate() {
+    return this._v
+  }
+
+  _reactToDependencyBecomingStale() {}
+}

packages/dataverse/src/derivations/DerivationEmitter.ts

@@ -0,0 +1,54 @@
+import type Ticker from '../Ticker'
+import Emitter from '../utils/Emitter'
+import type {default as Tappable} from '../utils/Tappable'
+import type {IDerivation} from './IDerivation'
+
+export default class DerivationEmitter<V> {
+  private _derivation: IDerivation<V>
+  private _ticker: Ticker
+  private _emitter: Emitter<V>
+  private _lastValue: undefined | V
+  private _lastValueRecorded: boolean
+  private _hadTappers: boolean
+
+  constructor(derivation: IDerivation<V>, ticker: Ticker) {
+    this._derivation = derivation
+    this._ticker = ticker
+    this._emitter = new Emitter()
+    this._emitter.onNumberOfTappersChange(() => {
+      this._reactToNumberOfTappersChange()
+    })
+    this._hadTappers = false
+    this._lastValueRecorded = false
+    this._lastValue = undefined
+    return this
+  }
+
+  private _possiblyMarkAsStale = () => {
+    this._ticker.onThisOrNextTick(this._refresh)
+  }
+
+  private _reactToNumberOfTappersChange() {
+    const hasTappers = this._emitter.hasTappers()
+    if (hasTappers !== this._hadTappers) {
+      this._hadTappers = hasTappers
+      if (hasTappers) {
+        this._derivation.addDependent(this._possiblyMarkAsStale)
+      } else {
+        this._derivation.removeDependent(this._possiblyMarkAsStale)
+      }
+    }
+  }
+
+  tappable(): Tappable<V> {
+    return this._emitter.tappable
+  }
+
+  private _refresh = () => {
+    const newValue = this._derivation.getValue()
+    if (newValue === this._lastValue && this._lastValueRecorded === true) return
+    this._lastValue = newValue
+    this._lastValueRecorded = true
+    this._emitter.emit(newValue)
+  }
+}

packages/dataverse/src/derivations/DerivationFromSource.ts

@@ -0,0 +1,53 @@
+import type {VoidFn} from '../types'
+import AbstractDerivation from './AbstractDerivation'
+
+const noop = () => {}
+
+export default class DerivationFromSource<V> extends AbstractDerivation<V> {
+  private _untapFromChanges: () => void
+  private _cachedValue: undefined | V
+  private _hasCachedValue: boolean
+
+  constructor(
+    private readonly _tapToSource: (listener: (newValue: V) => void) => VoidFn,
+    private readonly _getValueFromSource: () => V,
+  ) {
+    super()
+    this._untapFromChanges = noop
+    this._cachedValue = undefined
+    this._hasCachedValue = false
+  }
+
+  _recalculate() {
+    if (this.isHot) {
+      if (!this._hasCachedValue) {
+        this._cachedValue = this._getValueFromSource()
+        this._hasCachedValue = true
+      }
+      return this._cachedValue as V
+    } else {
+      return this._getValueFromSource()
+    }
+  }
+
+  _keepHot() {
+    this._hasCachedValue = false
+    this._cachedValue = undefined
+
+    this._untapFromChanges = this._tapToSource((newValue) => {
+      this._hasCachedValue = true
+      this._cachedValue = newValue
+      this._markAsStale(this)
+    })
+  }
+
+  _becomeCold() {
+    this._untapFromChanges()
+    this._untapFromChanges = noop
+
+    this._hasCachedValue = false
+    this._cachedValue = undefined
+  }
+
+  _reactToDependencyBecomingStale() {}
+}

packages/dataverse/src/derivations/DerivationValuelessEmitter.ts

@@ -0,0 +1,45 @@
+import Emitter from '../utils/Emitter'
+import type {default as Tappable} from '../utils/Tappable'
+import type {IDerivation} from './IDerivation'
+
+/**
+ * Just like DerivationEmitter, except it doesn't emit the value and doesn't need a ticker
+ */
+export default class DerivationValuelessEmitter<V> {
+  _derivation: IDerivation<V>
+  _emitter: Emitter<void>
+  _hadTappers: boolean
+
+  constructor(
+    derivation: IDerivation<V>,
+    readonly dontEmitValues: boolean = false,
+  ) {
+    this._derivation = derivation
+    this._emitter = new Emitter()
+    this._emitter.onNumberOfTappersChange(() => {
+      this._reactToNumberOfTappersChange()
+    })
+    this._hadTappers = false
+    return this
+  }
+
+  private _possiblyMarkAsStale = () => {
+    this._emitter.emit(undefined)
+  }
+
+  _reactToNumberOfTappersChange() {
+    const hasTappers = this._emitter.hasTappers()
+    if (hasTappers !== this._hadTappers) {
+      this._hadTappers = hasTappers
+      if (hasTappers) {
+        this._derivation.addDependent(this._possiblyMarkAsStale)
+      } else {
+        this._derivation.removeDependent(this._possiblyMarkAsStale)
+      }
+    }
+  }
+
+  tappable(): Tappable<void> {
+    return this._emitter.tappable
+  }
+}

packages/dataverse/src/derivations/IDerivation.ts

@@ -0,0 +1,28 @@
+import type Ticker from '../Ticker'
+import type {$IntentionalAny, VoidFn} from '../types'
+import type Tappable from '../utils/Tappable'
+
+type IDependent = (msgComingFrom: IDerivation<$IntentionalAny>) => void
+export interface IDerivation<V> {
+  isDerivation: true
+  isHot: boolean
+  changes(ticker: Ticker): Tappable<V>
+
+  changesWithoutValues(): Tappable<void>
+  keepHot(): VoidFn
+  tapImmediate(ticker: Ticker, fn: (cb: V) => void): VoidFn
+  addDependent(d: IDependent): void
+  removeDependent(d: IDependent): void
+
+  getValue(): V
+
+  map<T>(fn: (v: V) => T): IDerivation<T>
+
+  flatMap<R>(
+    fn: (v: V) => R,
+  ): IDerivation<R extends IDerivation<infer T> ? T : R>
+}
+
+export function isDerivation(d: any): d is IDerivation<unknown> {
+  return d && d.isDerivation && d.isDerivation === true
+}

packages/dataverse/src/derivations/flatMap.ts

@@ -0,0 +1,128 @@
+import type {$FixMe} from '../types'
+import AbstractDerivation from './AbstractDerivation'
+import type {IDerivation} from './IDerivation'
+import {isDerivation} from './IDerivation'
+
+enum UPDATE_NEEDED_FROM {
+  none = 0,
+  dep = 1,
+  inner = 2,
+}
+
+const makeFlatMapDerivationClass = () => {
+  class FlatMapDerivation<V, DepType> extends AbstractDerivation<V> {
+    private _innerDerivation: undefined | null | IDerivation<V>
+    private _staleDependency: UPDATE_NEEDED_FROM
+
+    static displayName = 'flatMap'
+
+    constructor(
+      readonly _depDerivation: IDerivation<DepType>,
+      readonly _fn: (v: DepType) => IDerivation<V> | V,
+    ) {
+      super()
+      this._innerDerivation = undefined
+      this._staleDependency = UPDATE_NEEDED_FROM.dep
+
+      this._addDependency(_depDerivation)
+
+      return this
+    }
+
+    _recalculateHot() {
+      const updateNeededFrom = this._staleDependency
+      this._staleDependency = UPDATE_NEEDED_FROM.none
+
+      if (updateNeededFrom === UPDATE_NEEDED_FROM.inner) {
+        // @ts-ignore
+        return this._innerDerivation.getValue()
+      }
+
+      const possibleInnerDerivation = this._fn(this._depDerivation.getValue())
+
+      if (isDerivation(possibleInnerDerivation)) {
+        this._innerDerivation = possibleInnerDerivation
+        this._addDependency(possibleInnerDerivation)
+        return possibleInnerDerivation.getValue()
+      } else {
+        return possibleInnerDerivation
+      }
+    }
+
+    protected _recalculateCold() {
+      const possibleInnerDerivation = this._fn(this._depDerivation.getValue())
+
+      if (isDerivation(possibleInnerDerivation)) {
+        return possibleInnerDerivation.getValue()
+      } else {
+        return possibleInnerDerivation
+      }
+    }
+
+    protected _recalculate() {
+      return this.isHot ? this._recalculateHot() : this._recalculateCold()
+    }
+
+    protected _reactToDependencyBecomingStale(
+      msgComingFrom: IDerivation<unknown>,
+    ) {
+      const updateNeededFrom =
+        msgComingFrom === this._depDerivation
+          ? UPDATE_NEEDED_FROM.dep
+          : UPDATE_NEEDED_FROM.inner
+
+      if (
+        updateNeededFrom === UPDATE_NEEDED_FROM.inner &&
+        msgComingFrom !== this._innerDerivation
+      ) {
+        throw Error(
+          `got a _reactToDependencyBecomingStale() from neither the dep nor the inner derivation`,
+        )
+      }
+
+      if (this._staleDependency === UPDATE_NEEDED_FROM.none) {
+        this._staleDependency = updateNeededFrom
+
+        if (updateNeededFrom === UPDATE_NEEDED_FROM.dep) {
+          this._removeInnerDerivation()
+        }
+      } else if (this._staleDependency === UPDATE_NEEDED_FROM.dep) {
+      } else {
+        if (updateNeededFrom === UPDATE_NEEDED_FROM.dep) {
+          this._staleDependency = UPDATE_NEEDED_FROM.dep
+          this._removeInnerDerivation()
+        }
+      }
+    }
+
+    private _removeInnerDerivation() {
+      if (this._innerDerivation) {
+        this._removeDependency(this._innerDerivation)
+        this._innerDerivation = undefined
+      }
+    }
+
+    protected _keepHot() {
+      this._staleDependency = UPDATE_NEEDED_FROM.dep
+      this.getValue()
+    }
+
+    protected _becomeCold() {
+      this._staleDependency = UPDATE_NEEDED_FROM.dep
+      this._removeInnerDerivation()
+    }
+  }
+  return FlatMapDerivation
+}
+
+let cls: ReturnType<typeof makeFlatMapDerivationClass> | undefined = undefined
+
+export default function flatMap<V, R>(
+  dep: IDerivation<V>,
+  fn: (v: V) => R,
+): IDerivation<R extends IDerivation<infer T> ? T : R> {
+  if (!cls) {
+    cls = makeFlatMapDerivationClass()
+  }
+  return new cls(dep, fn) as $FixMe
+}

packages/dataverse/src/derivations/iterateAndCountTicks.ts

@@ -0,0 +1,32 @@
+import {isPointer, valueDerivation} from '../Atom'
+import type {Pointer} from '../pointer'
+import type {IDerivation} from './IDerivation'
+import {isDerivation} from './IDerivation'
+
+export default function* iterateAndCountTicks<V>(
+  pointerOrDerivation: IDerivation<V> | Pointer<V>,
+): Generator<{value: V; ticks: number}, void, void> {
+  let d
+  if (isPointer(pointerOrDerivation)) {
+    d = valueDerivation(pointerOrDerivation) as IDerivation<V>
+  } else if (isDerivation(pointerOrDerivation)) {
+    d = pointerOrDerivation
+  } else {
+    throw new Error(`Only pointers and derivations are supported`)
+  }
+
+  let ticksCountedSinceLastYield = 0
+  const untap = d.changesWithoutValues().tap(() => {
+    ticksCountedSinceLastYield++
+  })
+
+  try {
+    while (true) {
+      const ticks = ticksCountedSinceLastYield
+      ticksCountedSinceLastYield = 0
+      yield {value: d.getValue(), ticks}
+    }
+  } finally {
+    untap()
+  }
+}

packages/dataverse/src/derivations/iterateOver.test.ts

@@ -0,0 +1,22 @@
+/**
+ * @jest-environment jsdom
+ */
+import Atom from '../Atom'
+import iterateOver from './iterateOver'
+
+describe(`iterateOver()`, () => {
+  test('it should work', () => {
+    const a = new Atom({a: 0})
+    let iter = iterateOver(a.pointer.a)
+    expect(iter.next().value).toEqual(0)
+    a.setIn(['a'], 1)
+    a.setIn(['a'], 2)
+    expect(iter.next()).toMatchObject({value: 2, done: false})
+    iter.return()
+    iter = iterateOver(a.pointer.a)
+    expect(iter.next().value).toEqual(2)
+    a.setIn(['a'], 3)
+    expect(iter.next()).toMatchObject({done: false, value: 3})
+    iter.return()
+  })
+})

packages/dataverse/src/derivations/iterateOver.ts

@@ -0,0 +1,32 @@
+import {isPointer, valueDerivation} from '../Atom'
+import type {Pointer} from '../pointer'
+import Ticker from '../Ticker'
+import type {IDerivation} from './IDerivation'
+import {isDerivation} from './IDerivation'
+
+export default function* iterateOver<V>(
+  pointerOrDerivation: IDerivation<V> | Pointer<V>,
+): Generator<V, void, void> {
+  let d
+  if (isPointer(pointerOrDerivation)) {
+    d = valueDerivation(pointerOrDerivation) as IDerivation<V>
+  } else if (isDerivation(pointerOrDerivation)) {
+    d = pointerOrDerivation
+  } else {
+    throw new Error(`Only pointers and derivations are supported`)
+  }
+
+  const ticker = new Ticker()
+
+  const untap = d.changes(ticker).tap((v) => {})
+
+  try {
+    while (true) {
+      ticker.tick()
+
+      yield d.getValue()
+    }
+  } finally {
+    untap()
+  }
+}

packages/dataverse/src/derivations/map.ts

@@ -0,0 +1,32 @@
+import AbstractDerivation from './AbstractDerivation'
+import type {IDerivation} from './IDerivation'
+
+// Exporting from a function because of the circular dependency with AbstractDerivation
+const makeMapDerivationClass = () =>
+  class MapDerivation<T, V> extends AbstractDerivation<V> {
+    constructor(
+      private readonly _dep: IDerivation<T>,
+      private readonly _fn: (t: T) => V,
+    ) {
+      super()
+      this._addDependency(_dep)
+    }
+
+    _recalculate() {
+      return this._fn(this._dep.getValue())
+    }
+
+    _reactToDependencyBecomingStale() {}
+  }
+
+let cls: ReturnType<typeof makeMapDerivationClass> | undefined = undefined
+
+export default function flatMap<V, R>(
+  dep: IDerivation<V>,
+  fn: (v: V) => R,
+): IDerivation<R> {
+  if (!cls) {
+    cls = makeMapDerivationClass()
+  }
+  return new cls(dep, fn)
+}

packages/dataverse/src/derivations/prism/discoveryMechanism.ts

@@ -0,0 +1,94 @@
+import type {$IntentionalAny} from '../../types'
+import Stack from '../../utils/Stack'
+import type {IDerivation} from '../IDerivation'
+
+function createMechanism() {
+  const noop = () => {}
+
+  const stack = new Stack<Collector>()
+  const noopCollector: Collector = noop
+
+  type Collector = (d: IDerivation<$IntentionalAny>) => void
+
+  const collectObservedDependencies = (
+    cb: () => void,
+    collector: Collector,
+  ) => {
+    stack.push(collector)
+    cb()
+    stack.pop()
+  }
+
+  const startIgnoringDependencies = () => {
+    stack.push(noopCollector)
+  }
+
+  const stopIgnoringDependencies = () => {
+    if (stack.peek() !== noopCollector) {
+      if (process.env.NODE_ENV === 'development') {
+        console.warn('This should never happen')
+      }
+    } else {
+      stack.pop()
+    }
+  }
+
+  const reportResolutionStart = (d: IDerivation<$IntentionalAny>) => {
+    const possibleCollector = stack.peek()
+    if (possibleCollector) {
+      possibleCollector(d)
+    }
+
+    stack.push(noopCollector)
+  }
+
+  const reportResolutionEnd = (_d: IDerivation<$IntentionalAny>) => {
+    stack.pop()
+  }
+
+  const isCollectingDependencies = () => {
+    return stack.peek() !== noopCollector
+  }
+
+  return {
+    type: 'Dataverse_discoveryMechanism' as 'Dataverse_discoveryMechanism',
+    collectObservedDependencies,
+    startIgnoringDependencies,
+    stopIgnoringDependencies,
+    reportResolutionStart,
+    reportResolutionEnd,
+    isCollectingDependencies,
+  }
+}
+
+function getSharedMechanism(): ReturnType<typeof createMechanism> {
+  const varName = '__dataverse_discoveryMechanism_sharedStack'
+  if (global) {
+    const existingMechanism: ReturnType<typeof createMechanism> | undefined =
+      // @ts-ignore ignore
+      global[varName]
+    if (
+      existingMechanism &&
+      typeof existingMechanism === 'object' &&
+      existingMechanism.type === 'Dataverse_discoveryMechanism'
+    ) {
+      return existingMechanism
+    } else {
+      const mechanism = createMechanism()
+      // @ts-ignore ignore
+      global[varName] = mechanism
+      return mechanism
+    }
+  } else {
+    return createMechanism()
+  }
+}
+
+export const {
+  collectObservedDependencies,
+  startIgnoringDependencies,
+  stopIgnoringDependencies,
+  reportResolutionEnd,
+  reportResolutionStart,
+  isCollectingDependencies,
+} = getSharedMechanism()

packages/dataverse/src/derivations/prism/prism.test.ts

@@ -0,0 +1,228 @@
+/**
+ * @jest-environment jsdom
+ */
+import Atom, {val} from '../../Atom'
+import Ticker from '../../Ticker'
+import type {$FixMe, $IntentionalAny} from '../../types'
+import ConstantDerivation from '../ConstantDerivation'
+import iterateAndCountTicks from '../iterateAndCountTicks'
+import prism, {PrismDerivation} from './prism'
+
+describe('prism', () => {
+  let ticker: Ticker
+  beforeEach(() => {
+    ticker = new Ticker()
+  })
+
+  it('should work', () => {
+    const o = new Atom({foo: 'foo'})
+    const d = new PrismDerivation(() => {
+      return val(o.pointer.foo) + 'boo'
+    })
+    expect(d.getValue()).toEqual('fooboo')
+
+    const changes: Array<$FixMe> = []
+    d.changes(ticker).tap((c) => {
+      changes.push(c)
+    })
+
+    o.reduceState(['foo'], () => 'foo2')
+    ticker.tick()
+    expect(changes).toMatchObject(['foo2boo'])
+  })
+  it('should only collect immediate dependencies', () => {
+    const aD = new ConstantDerivation(1)
+    const bD = aD.map((v) => v * 2)
+    const cD = prism(() => {
+      return bD.getValue()
+    })
+    expect(cD.getValue()).toEqual(2)
+    expect((cD as $IntentionalAny)._dependencies.size).toEqual(1)
+  })
+
+  describe('prism.ref()', () => {
+    it('should work', () => {
+      const theAtom: Atom<{n: number}> = new Atom({n: 2})
+
+      const isEvenD = prism((): {isEven: boolean} => {
+        const ref = prism.ref<{isEven: boolean} | undefined>('cache', undefined)
+        const currentN = val(theAtom.pointer.n)
+
+        const isEven = currentN % 2 === 0
+        if (ref.current && ref.current.isEven === isEven) {
+          return ref.current
+        } else {
+          ref.current = {isEven}
+          return ref.current
+        }
+      })
+
+      const iterator = iterateAndCountTicks(isEvenD)
+
+      theAtom.reduceState(['n'], () => 3)
+
+      expect(iterator.next().value).toMatchObject({
+        value: {isEven: false},
+        ticks: 0,
+      })
+      theAtom.reduceState(['n'], () => 5)
+      theAtom.reduceState(['n'], () => 7)
+      expect(iterator.next().value).toMatchObject({
+        value: {isEven: false},
+        ticks: 1,
+      })
+      theAtom.reduceState(['n'], () => 2)
+      theAtom.reduceState(['n'], () => 4)
+      expect(iterator.next().value).toMatchObject({
+        value: {isEven: true},
+        ticks: 1,
+      })
+      expect(iterator.next().value).toMatchObject({
+        value: {isEven: true},
+        ticks: 0,
+      })
+    })
+  })
+
+  describe('prism.effect()', () => {
+    it('should work', async () => {
+      let iteration = 0
+      const sequence: unknown[] = []
+      let deps: unknown[] = []
+
+      const a = new Atom({letter: 'a'})
+
+      const derivation = prism(() => {
+        const n = val(a.pointer.letter)
+        const iterationAtTimeOfCall = iteration
+        sequence.push({derivationCall: iterationAtTimeOfCall})
+
+        prism.effect(
+          'f',
+          () => {
+            sequence.push({effectCall: iterationAtTimeOfCall})
+            return () => {
+              sequence.push({cleanupCall: iterationAtTimeOfCall})
+            }
+          },
+          [...deps],
+        )
+
+        return n
+      })
+
+      const untap = derivation.changes(ticker).tap((change) => {
+        sequence.push({change})
+      })
+
+      expect(sequence).toMatchObject([{derivationCall: 0}, {effectCall: 0}])
+      sequence.length = 0
+
+      iteration++
+      a.setIn(['letter'], 'b')
+      ticker.tick()
+      expect(sequence).toMatchObject([{derivationCall: 1}, {change: 'b'}])
+      sequence.length = 0
+
+      deps = [1]
+      iteration++
+      a.setIn(['letter'], 'c')
+      ticker.tick()
+      expect(sequence).toMatchObject([
+        {derivationCall: 2},
+        {cleanupCall: 0},
+        {effectCall: 2},
+        {change: 'c'},
+      ])
+      sequence.length = 0
+
+      untap()
+
+      // takes a tick before untap takes effect
+      await new Promise((resolve) => setTimeout(resolve, 1))
+      expect(sequence).toMatchObject([{cleanupCall: 2}])
+    })
+  })
+
+  describe('prism.memo()', () => {
+    it('should work', async () => {
+      let iteration = 0
+      const sequence: unknown[] = []
+      let deps: unknown[] = []
+
+      const a = new Atom({letter: 'a'})
+
+      const derivation = prism(() => {
+        const n = val(a.pointer.letter)
+        const iterationAtTimeOfCall = iteration
+        sequence.push({derivationCall: iterationAtTimeOfCall})
+
+        const resultOfMemo = prism.memo(
+          'memo',
+          () => {
+            sequence.push({memoCall: iterationAtTimeOfCall})
+            return iterationAtTimeOfCall
+          },
+          [...deps],
+        )
+
+        sequence.push({resultOfMemo})
+
+        return n
+      })
+
+      const untap = derivation.changes(ticker).tap((change) => {
+        sequence.push({change})
+      })
+
+      expect(sequence).toMatchObject([
+        {derivationCall: 0},
+        {memoCall: 0},
+        {resultOfMemo: 0},
+      ])
+      sequence.length = 0
+
+      iteration++
+      a.setIn(['letter'], 'b')
+      ticker.tick()
+      expect(sequence).toMatchObject([
+        {derivationCall: 1},
+        {resultOfMemo: 0},
+        {change: 'b'},
+      ])
+      sequence.length = 0
+
+      deps = [1]
+      iteration++
+      a.setIn(['letter'], 'c')
+      ticker.tick()
+      expect(sequence).toMatchObject([
+        {derivationCall: 2},
+        {memoCall: 2},
+        {resultOfMemo: 2},
+        {change: 'c'},
+      ])
+      sequence.length = 0
+
+      untap()
+    })
+  })
+
+  describe(`prism.scope()`, () => {
+    it('should prevent name conflicts', () => {
+      const d = prism(() => {
+        const thisNameWillBeUsedForBothMemos = 'blah'
+        const a = prism.scope('a', () => {
+          return prism.memo(thisNameWillBeUsedForBothMemos, () => 'a', [])
+        })
+
+        const b = prism.scope('b', () => {
+          return prism.memo(thisNameWillBeUsedForBothMemos, () => 'b', [])
+        })
+
+        return {a, b}
+      })
+      expect(d.getValue()).toMatchObject({a: 'a', b: 'b'})
+    })
+  })
+})

packages/dataverse/src/derivations/prism/prism.ts

@@ -0,0 +1,347 @@
+import Box from '../../Box'
+import type {$IntentionalAny, VoidFn} from '../../types'
+import Stack from '../../utils/Stack'
+import AbstractDerivation from '../AbstractDerivation'
+import type {IDerivation} from '../IDerivation'
+import {
+  collectObservedDependencies,
+  startIgnoringDependencies,
+  stopIgnoringDependencies,
+} from './discoveryMechanism'
+
+const voidFn = () => {}
+
+export class PrismDerivation<V> extends AbstractDerivation<V> {
+  protected _cacheOfDendencyValues: Map<IDerivation<unknown>, unknown> =
+    new Map()
+  protected _possiblyStaleDeps = new Set<IDerivation<unknown>>()
+  private _prismScope = new PrismScope()
+
+  constructor(readonly _fn: () => V) {
+    super()
+  }
+
+  _recalculate() {
+    let value: V
+
+    if (this._possiblyStaleDeps.size > 0) {
+      let anActuallyStaleDepWasFound = false
+      startIgnoringDependencies()
+      for (const dep of this._possiblyStaleDeps) {
+        if (this._cacheOfDendencyValues.get(dep) !== dep.getValue()) {
+          anActuallyStaleDepWasFound = true
+          break
+        }
+      }
+      stopIgnoringDependencies()
+      this._possiblyStaleDeps.clear()
+      if (!anActuallyStaleDepWasFound) {
+        // console.log('ok')
+
+        return this._lastValue!
+      }
+    }
+
+    const newDeps: Set<IDerivation<unknown>> = new Set()
+    this._cacheOfDendencyValues.clear()
+    collectObservedDependencies(
+      () => {
+        hookScopeStack.push(this._prismScope)
+        try {
+          value = this._fn()
+        } catch (error) {
+          console.error(error)
+        } finally {
+          const topOfTheStack = hookScopeStack.pop()
+          if (topOfTheStack !== this._prismScope) {
+            console.warn(
+              // @todo guide the user to report the bug in an issue
+              `The Prism hook stack has slipped. This is a bug.`,
+            )
+          }
+        }
+      },
+      (observedDep) => {
+        newDeps.add(observedDep)
+        this._addDependency(observedDep)
+      },
+    )
+
+    this._dependencies.forEach((dep) => {
+      if (!newDeps.has(dep)) {
+        this._removeDependency(dep)
+      }
+    })
+
+    this._dependencies = newDeps
+
+    startIgnoringDependencies()
+    newDeps.forEach((dep) => {
+      this._cacheOfDendencyValues.set(dep, dep.getValue())
+    })
+    stopIgnoringDependencies()
+
+    return value!
+  }
+
+  _reactToDependencyBecomingStale(msgComingFrom: IDerivation<unknown>) {
+    this._possiblyStaleDeps.add(msgComingFrom)
+  }
+
+  _keepHot() {
+    this._prismScope = new PrismScope()
+    startIgnoringDependencies()
+    this.getValue()
+    stopIgnoringDependencies()
+  }
+
+  _becomeCold() {
+    cleanupScopeStack(this._prismScope)
+    this._prismScope = new PrismScope()
+  }
+}
+
+class PrismScope {
+  isPrismScope = true
+  private _subs: Record<string, PrismScope> = {}
+
+  sub(key: string) {
+    if (!this._subs[key]) {
+      this._subs[key] = new PrismScope()
+    }
+    return this._subs[key]
+  }
+
+  get subs() {
+    return this._subs
+  }
+}
+
+function cleanupScopeStack(scope: PrismScope) {
+  for (const [_, sub] of Object.entries(scope.subs)) {
+    cleanupScopeStack(sub)
+  }
+  cleanupEffects(scope)
+}
+
+function cleanupEffects(scope: PrismScope) {
+  const effects = effectsWeakMap.get(scope)
+  if (effects) {
+    for (const k of Object.keys(effects)) {
+      const effect = effects[k]
+      safelyRun(effect.cleanup, undefined)
+    }
+  }
+  effectsWeakMap.delete(scope)
+}
+
+function safelyRun<T, U>(
+  fn: () => T,
+  returnValueInCaseOfError: U,
+): {success: boolean; returnValue: T | U} {
+  let returnValue: T | U = returnValueInCaseOfError
+  let success = false
+  try {
+    returnValue = fn()
+    success = true
+  } catch (error) {
+    setTimeout(() => {
+      throw error
+    })
+  }
+  return {success, returnValue}
+}
+
+const hookScopeStack = new Stack<PrismScope>()
+
+const refsWeakMap = new WeakMap<PrismScope, Record<string, IRef<unknown>>>()
+
+type IRef<T> = {
+  current: T
+}
+const effectsWeakMap = new WeakMap<PrismScope, Record<string, IEffect>>()
+
+type IEffect = {
+  deps: undefined | unknown[]
+  cleanup: VoidFn
+}
+
+const memosWeakMap = new WeakMap<PrismScope, Record<string, IMemo>>()
+
+type IMemo = {
+  deps: undefined | unknown[]
+  cachedValue: unknown
+}
+
+function ref<T>(key: string, initialValue: T): IRef<T> {
+  const scope = hookScopeStack.peek()
+  if (!scope) {
+    throw new Error(`prism.ref() is called outside of a prism() call.`)
+  }
+  let refs = refsWeakMap.get(scope)
+  if (!refs) {
+    refs = {}
+    refsWeakMap.set(scope, refs)
+  }
+
+  if (refs[key]) {
+    return refs[key] as $IntentionalAny as IRef<T>
+  } else {
+    const ref: IRef<T> = {
+      current: initialValue,
+    }
+    refs[key] = ref
+    return ref
+  }
+}
+
+function effect(key: string, cb: () => () => void, deps?: unknown[]): void {
+  const scope = hookScopeStack.peek()
+  if (!scope) {
+    throw new Error(`prism.effect() is called outside of a prism() call.`)
+  }
+  let effects = effectsWeakMap.get(scope)
+
+  if (!effects) {
+    effects = {}
+    effectsWeakMap.set(scope, effects)
+  }
+
+  if (!effects[key]) {
+    effects[key] = {
+      cleanup: voidFn,
+      deps: [{}],
+    }
+  }
+
+  const effect = effects[key]
+  if (depsHaveChanged(effect.deps, deps)) {
+    effect.cleanup()
+
+    startIgnoringDependencies()
+    effect.cleanup = safelyRun(cb, voidFn).returnValue
+    stopIgnoringDependencies()
+    effect.deps = deps
+  }
+}
+
+function depsHaveChanged(
+  oldDeps: undefined | unknown[],
+  newDeps: undefined | unknown[],
+): boolean {
+  if (oldDeps === undefined || newDeps === undefined) {
+    return true
+  } else if (oldDeps.length !== newDeps.length) {
+    return true
+  } else {
+    return oldDeps.some((el, i) => el !== newDeps[i])
+  }
+}
+
+function memo<T>(
+  key: string,
+  fn: () => T,
+  deps: undefined | $IntentionalAny[],
+): T {
+  const scope = hookScopeStack.peek()
+  if (!scope) {
+    throw new Error(`prism.memo() is called outside of a prism() call.`)
+  }
+
+  let memos = memosWeakMap.get(scope)
+
+  if (!memos) {
+    memos = {}
+    memosWeakMap.set(scope, memos)
+  }
+
+  if (!memos[key]) {
+    memos[key] = {
+      cachedValue: null,
+      deps: [{}],
+    }
+  }
+
+  const memo = memos[key]
+  if (depsHaveChanged(memo.deps, deps)) {
+    startIgnoringDependencies()
+
+    memo.cachedValue = safelyRun(fn, undefined).returnValue
+    stopIgnoringDependencies()
+    memo.deps = deps
+  }
+
+  return memo.cachedValue as $IntentionalAny as T
+}
+
+function state<T>(key: string, initialValue: T): [T, (val: T) => void] {
+  const {b, setValue} = prism.memo(
+    'state/' + key,
+    () => {
+      const b = new Box<T>(initialValue)
+      const setValue = (val: T) => b.set(val)
+      return {b, setValue}
+    },
+    [],
+  )
+
+  return [b.derivation.getValue(), setValue]
+}
+
+function ensurePrism(): void {
+  const scope = hookScopeStack.peek()
+  if (!scope) {
+    throw new Error(`The parent function is called outside of a prism() call.`)
+  }
+}
+
+function scope<T>(key: string, fn: () => T): T {
+  const parentScope = hookScopeStack.peek()
+  if (!parentScope) {
+    throw new Error(`prism.scope() is called outside of a prism() call.`)
+  }
+  const subScope = parentScope.sub(key)
+  hookScopeStack.push(subScope)
+  const ret = safelyRun(fn, undefined).returnValue
+  hookScopeStack.pop()
+  return ret as $IntentionalAny as T
+}
+
+function sub<T>(
+  key: string,
+  fn: () => T,
+  deps: undefined | $IntentionalAny[],
+): T {
+  return memo(key, () => prism(fn), deps).getValue()
+}
+
+function inPrism(): boolean {
+  return !!hookScopeStack.peek()
+}
+
+type IPrismFn = {
+  <T>(fn: () => T): IDerivation<T>
+  ref: typeof ref
+  effect: typeof effect
+  memo: typeof memo
+  ensurePrism: typeof ensurePrism
+  state: typeof state
+  scope: typeof scope
+  sub: typeof sub
+  inPrism: typeof inPrism
+}
+
+const prism: IPrismFn = (fn) => {
+  return new PrismDerivation(fn)
+}
+
+prism.ref = ref
+prism.effect = effect
+prism.memo = memo
+prism.ensurePrism = ensurePrism
+prism.state = state
+prism.scope = scope
+prism.sub = sub
+prism.inPrism = inPrism
+
+export default prism

packages/dataverse/src/index.ts

@@ -0,0 +1,15 @@
+export {default as Atom, isPointer, val, valueDerivation} from './Atom'
+export {default as Box} from './Box'
+export type {IBox} from './Box'
+export {default as AbstractDerivation} from './derivations/AbstractDerivation'
+export {default as ConstantDerivation} from './derivations/ConstantDerivation'
+export {default as DerivationFromSource} from './derivations/DerivationFromSource'
+export {isDerivation} from './derivations/IDerivation'
+export type {IDerivation} from './derivations/IDerivation'
+export {default as iterateAndCountTicks} from './derivations/iterateAndCountTicks'
+export {default as iterateOver} from './derivations/iterateOver'
+export {default as prism} from './derivations/prism/prism'
+export {default as pointer, getPointerParts} from './pointer'
+export type {Pointer} from './pointer'
+export {default as Ticker} from './Ticker'
+export {default as PointerProxy} from './PointerProxy'

packages/dataverse/src/integration.test.ts

@@ -0,0 +1,35 @@
+/**
+ * @jest-environment jsdom
+ */
+import Atom, {val} from './Atom'
+import prism from './derivations/prism/prism'
+import Ticker from './Ticker'
+
+describe(`v2 atom`, () => {
+  describe(`identity pointers`, () => {
+    it(`should work`, () => {
+      const data = {foo: 'hi', bar: 0}
+      const a = new Atom(data)
+      const dataP = a.pointer
+      const bar = dataP.bar
+      expect(val(bar)).toEqual(0)
+
+      const d = prism(() => {
+        return val(bar)
+      })
+      expect(d.getValue()).toEqual(0)
+      const ticker = new Ticker()
+      const changes: number[] = []
+      d.changes(ticker).tap((c) => {
+        changes.push(c)
+      })
+      a.setState({...data, bar: 1})
+      ticker.tick()
+      expect(changes).toHaveLength(1)
+      expect(changes[0]).toEqual(1)
+      a.setState({...data, bar: 1})
+      ticker.tick()
+      expect(changes).toHaveLength(1)
+    })
+  })
+})

packages/dataverse/src/pointer.ts

@@ -0,0 +1,104 @@
+import type {$IntentionalAny} from './types'
+
+type PathToProp = Array<string | number>
+
+type PointerMeta = {
+  root: {}
+  path: (string | number)[]
+}
+
+export type UnindexableTypesForPointer =
+  | number
+  | string
+  | boolean
+  | null
+  | void
+  | undefined
+  | Function // eslint-disable-line @typescript-eslint/ban-types
+
+export type UnindexablePointer = {
+  [K in $IntentionalAny]: Pointer<undefined>
+}
+
+const pointerMetaWeakMap = new WeakMap<{}, PointerMeta>()
+
+export type PointerType<O> = {
+  $$__pointer_type: O
+}
+
+export type Pointer<O> = PointerType<O> &
+  (O extends UnindexableTypesForPointer
+    ? UnindexablePointer
+    : unknown extends O
+    ? UnindexablePointer
+    : O extends (infer T)[]
+    ? Pointer<T>[]
+    : O extends {}
+    ? {
+        [K in keyof O]-?: Pointer<O[K]>
+      } /*&
+        {[K in string | number]: Pointer<K extends keyof O ? O[K] : undefined>}*/
+    : UnindexablePointer)
+
+const pointerMetaSymbol = Symbol('pointerMeta')
+
+const cachedSubPointersWeakMap = new WeakMap<
+  {},
+  Record<string | number, Pointer<unknown>>
+>()
+
+const handler = {
+  get(obj: {}, prop: string | typeof pointerMetaSymbol): $IntentionalAny {
+    if (prop === pointerMetaSymbol) return pointerMetaWeakMap.get(obj)!
+
+    let subs = cachedSubPointersWeakMap.get(obj)
+    if (!subs) {
+      subs = {}
+      cachedSubPointersWeakMap.set(obj, subs)
+    }
+
+    if (subs[prop]) return subs[prop]
+
+    const meta = pointerMetaWeakMap.get(obj)!
+
+    const subPointer = pointer({root: meta.root, path: [...meta.path, prop]})
+    subs[prop] = subPointer
+    return subPointer
+  },
+}
+
+export const getPointerMeta = (
+  p: Pointer<$IntentionalAny> | Pointer<{}> | Pointer<unknown>,
+): PointerMeta => {
+  // @ts-ignore @todo
+  const meta: PointerMeta = p[
+    pointerMetaSymbol as unknown as $IntentionalAny
+  ] as $IntentionalAny
+  return meta
+}
+
+export const getPointerParts = (
+  p: Pointer<$IntentionalAny> | Pointer<{}> | Pointer<unknown>,
+): {root: {}; path: PathToProp} => {
+  const {root, path} = getPointerMeta(p)
+  return {root, path}
+}
+
+function pointer<O>({
+  root,
+  path,
+}: {
+  root: {}
+  path: Array<string | number>
+}): Pointer<O>
+function pointer(args: {root: {}; path?: Array<string | number>}) {
+  const meta: PointerMeta = {
+    root: args.root as $IntentionalAny,
+    path: args.path ?? [],
+  }
+  const hiddenObj = {}
+  pointerMetaWeakMap.set(hiddenObj, meta)
+  return new Proxy(hiddenObj, handler) as Pointer<$IntentionalAny>
+}
+
+export default pointer

packages/dataverse/src/setupTestEnv.ts

@@ -0,0 +1 @@
+export {}

packages/dataverse/src/types.ts

@@ -0,0 +1,6 @@
+/** For `any`s that aren't meant to stay `any`*/
+export type $FixMe = any
+/** For `any`s that we don't care about */
+export type $IntentionalAny = any
+
+export type VoidFn = () => void

packages/dataverse/src/utils/Emitter.test.ts

@@ -0,0 +1,19 @@
+import Emitter from './Emitter'
+
+describe.only('DataVerse.Emitter', () => {
+  it('should work', () => {
+    const e: Emitter<string> = new Emitter()
+    e.emit('no one will see this')
+    e.emit('nor this')
+
+    const tappedEvents: string[] = []
+    const untap = e.tappable.tap((payload) => {
+      tappedEvents.push(payload)
+    })
+    e.emit('foo')
+    e.emit('bar')
+    untap()
+    e.emit('baz')
+    expect(tappedEvents).toMatchObject(['foo', 'bar'])
+  })
+})

packages/dataverse/src/utils/Emitter.ts

@@ -0,0 +1,55 @@
+import Tappable from './Tappable'
+
+type Tapper<V> = (v: V) => void
+type Untap = () => void
+
+export default class Emitter<V> {
+  private _tappers: Map<any, (v: V) => void>
+  private _lastTapperId: number
+  readonly tappable: Tappable<V>
+  private _onNumberOfTappersChangeListener: undefined | ((n: number) => void)
+
+  constructor() {
+    this._lastTapperId = 0
+    this._tappers = new Map()
+    this.tappable = new Tappable({
+      tapToSource: (cb: Tapper<V>) => {
+        return this._tap(cb)
+      },
+    })
+  }
+
+  _tap(cb: Tapper<V>): Untap {
+    const tapperId = this._lastTapperId++
+    this._tappers.set(tapperId, cb)
+    this._onNumberOfTappersChangeListener &&
+      this._onNumberOfTappersChangeListener(this._tappers.size)
+    return () => {
+      this._removeTapperById(tapperId)
+    }
+  }
+
+  _removeTapperById(id: number) {
+    const oldSize = this._tappers.size
+    this._tappers.delete(id)
+    const newSize = this._tappers.size
+    if (oldSize !== newSize) {
+      this._onNumberOfTappersChangeListener &&
+        this._onNumberOfTappersChangeListener(this._tappers.size)
+    }
+  }
+
+  emit(payload: V) {
+    this._tappers.forEach((cb) => {
+      cb(payload)
+    })
+  }
+
+  hasTappers() {
+    return this._tappers.size !== 0
+  }
+
+  onNumberOfTappersChange(cb: (n: number) => void) {
+    this._onNumberOfTappersChangeListener = cb
+  }
+}

packages/dataverse/src/utils/EventEmitter.ts

@@ -0,0 +1,56 @@
+import forEach from 'lodash-es/forEach'
+import without from 'lodash-es/without'
+import type {$FixMe} from '../types'
+
+type Listener = (v: $FixMe) => void
+
+/**
+ * A simple barebones event emitter
+ */
+export default class EventEmitter {
+  _listenersByType: {[eventName: string]: Array<Listener>}
+  constructor() {
+    this._listenersByType = {}
+  }
+
+  addEventListener(eventName: string, listener: Listener) {
+    const listeners =
+      this._listenersByType[eventName] ||
+      (this._listenersByType[eventName] = [])
+
+    listeners.push(listener)
+
+    return this
+  }
+
+  removeEventListener(eventName: string, listener: Listener) {
+    const listeners = this._listenersByType[eventName]
+    if (listeners) {
+      const newListeners = without(listeners, listener)
+      if (newListeners.length === 0) {
+        delete this._listenersByType[eventName]
+      } else {
+        this._listenersByType[eventName] = newListeners
+      }
+    }
+
+    return this
+  }
+
+  emit(eventName: string, payload: unknown) {
+    const listeners = this.getListenersFor(eventName)
+    if (listeners) {
+      forEach(listeners, (listener) => {
+        listener(payload)
+      })
+    }
+  }
+
+  getListenersFor(eventName: string) {
+    return this._listenersByType[eventName]
+  }
+
+  hasListenersFor(eventName: string) {
+    return this.getListenersFor(eventName) ? true : false
+  }
+}

packages/dataverse/src/utils/PathBasedReducer.ts

@@ -0,0 +1,133 @@
+export type PathBasedReducer<S, ReturnType> = {
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+    A5 extends keyof S[A0][A1][A2][A3][A4],
+    A6 extends keyof S[A0][A1][A2][A3][A4][A5],
+    A7 extends keyof S[A0][A1][A2][A3][A4][A5][A6],
+    A8 extends keyof S[A0][A1][A2][A3][A4][A5][A6][A7],
+    A9 extends keyof S[A0][A1][A2][A3][A4][A5][A6][A7][A8],
+    A10 extends keyof S[A0][A1][A2][A3][A4][A5][A6][A7][A8][A9],
+  >(
+    addr: [A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10],
+    reducer: (
+      d: S[A0][A1][A2][A3][A4][A5][A6][A7][A8][A9][A10],
+    ) => S[A0][A1][A2][A3][A4][A5][A6][A7][A8][A9][A10],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+    A5 extends keyof S[A0][A1][A2][A3][A4],
+    A6 extends keyof S[A0][A1][A2][A3][A4][A5],
+    A7 extends keyof S[A0][A1][A2][A3][A4][A5][A6],
+    A8 extends keyof S[A0][A1][A2][A3][A4][A5][A6][A7],
+    A9 extends keyof S[A0][A1][A2][A3][A4][A5][A6][A7][A8],
+  >(
+    addr: [A0, A1, A2, A3, A4, A5, A6, A7, A8, A9],
+    reducer: (
+      d: S[A0][A1][A2][A3][A4][A5][A6][A7][A8][A9],
+    ) => S[A0][A1][A2][A3][A4][A5][A6][A7][A8][A9],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+    A5 extends keyof S[A0][A1][A2][A3][A4],
+    A6 extends keyof S[A0][A1][A2][A3][A4][A5],
+    A7 extends keyof S[A0][A1][A2][A3][A4][A5][A6],
+    A8 extends keyof S[A0][A1][A2][A3][A4][A5][A6][A7],
+  >(
+    addr: [A0, A1, A2, A3, A4, A5, A6, A7, A8],
+    reducer: (
+      d: S[A0][A1][A2][A3][A4][A5][A6][A7][A8],
+    ) => S[A0][A1][A2][A3][A4][A5][A6][A7][A8],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+    A5 extends keyof S[A0][A1][A2][A3][A4],
+    A6 extends keyof S[A0][A1][A2][A3][A4][A5],
+    A7 extends keyof S[A0][A1][A2][A3][A4][A5][A6],
+  >(
+    addr: [A0, A1, A2, A3, A4, A5, A6, A7],
+    reducer: (
+      d: S[A0][A1][A2][A3][A4][A5][A6][A7],
+    ) => S[A0][A1][A2][A3][A4][A5][A6][A7],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+    A5 extends keyof S[A0][A1][A2][A3][A4],
+    A6 extends keyof S[A0][A1][A2][A3][A4][A5],
+  >(
+    addr: [A0, A1, A2, A3, A4, A5, A6],
+    reducer: (
+      d: S[A0][A1][A2][A3][A4][A5][A6],
+    ) => S[A0][A1][A2][A3][A4][A5][A6],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+    A5 extends keyof S[A0][A1][A2][A3][A4],
+  >(
+    addr: [A0, A1, A2, A3, A4, A5],
+    reducer: (d: S[A0][A1][A2][A3][A4][A5]) => S[A0][A1][A2][A3][A4][A5],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+  >(
+    addr: [A0, A1, A2, A3, A4],
+    reducer: (d: S[A0][A1][A2][A3][A4]) => S[A0][A1][A2][A3][A4],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+  >(
+    addr: [A0, A1, A2, A3],
+    reducer: (d: S[A0][A1][A2][A3]) => S[A0][A1][A2][A3],
+  ): ReturnType
+
+  <A0 extends keyof S, A1 extends keyof S[A0], A2 extends keyof S[A0][A1]>(
+    addr: [A0, A1, A2],
+    reducer: (d: S[A0][A1][A2]) => S[A0][A1][A2],
+  ): ReturnType
+
+  <A0 extends keyof S, A1 extends keyof S[A0]>(
+    addr: [A0, A1],
+    reducer: (d: S[A0][A1]) => S[A0][A1],
+  ): ReturnType
+
+  <A0 extends keyof S>(addr: [A0], reducer: (d: S[A0]) => S[A0]): ReturnType
+
+  (addr: undefined[], reducer: (d: S) => S): ReturnType
+}

packages/dataverse/src/utils/Stack.ts

@@ -0,0 +1,33 @@
+interface Node<Data> {
+  next: undefined | Node<Data>
+  data: Data
+}
+
+/**
+ * Just a simple LinkedList
+ */
+export default class Stack<Data> {
+  _head: undefined | Node<Data>
+
+  constructor() {
+    this._head = undefined
+  }
+
+  peek() {
+    return this._head && this._head.data
+  }
+
+  pop() {
+    const head = this._head
+    if (!head) {
+      return undefined
+    }
+    this._head = head.next
+    return head.data
+  }
+
+  push(data: Data) {
+    const node = {next: this._head, data}
+    this._head = node
+  }
+}

packages/dataverse/src/utils/Tappable.ts

@@ -0,0 +1,91 @@
+type Untap = () => void
+type UntapFromSource = () => void
+
+interface IProps<V> {
+  tapToSource: (cb: (payload: V) => void) => UntapFromSource
+}
+
+type Listener<V> = ((v: V) => void) | (() => void)
+
+export default class Tappable<V> {
+  private _props: IProps<V>
+  private _tappers: Map<number, {bivarianceHack(v: V): void}['bivarianceHack']>
+  private _untapFromSource: null | UntapFromSource
+  private _lastTapperId: number
+  private _untapFromSourceTimeout: null | NodeJS.Timer = null
+
+  constructor(props: IProps<V>) {
+    this._lastTapperId = 0
+    this._untapFromSource = null
+    this._props = props
+    this._tappers = new Map()
+  }
+
+  private _check() {
+    if (this._untapFromSource) {
+      if (this._tappers.size === 0) {
+        this._scheduleToUntapFromSource()
+        /*
+         * this._untapFromSource()
+         * this._untapFromSource = null
+         */
+      }
+    } else {
+      if (this._tappers.size !== 0) {
+        this._untapFromSource = this._props.tapToSource(this._cb)
+      }
+    }
+  }
+
+  private _scheduleToUntapFromSource() {
+    if (this._untapFromSourceTimeout !== null) return
+    this._untapFromSourceTimeout = setTimeout(() => {
+      this._untapFromSourceTimeout = null
+      if (this._tappers.size === 0) {
+        this._untapFromSource!()
+
+        this._untapFromSource = null
+      }
+    }, 0)
+  }
+
+  private _cb: any = (arg: any): void => {
+    this._tappers.forEach((cb) => {
+      cb(arg)
+    })
+  }
+
+  tap(cb: Listener<V>): Untap {
+    const tapperId = this._lastTapperId++
+    this._tappers.set(tapperId, cb)
+    this._check()
+    return () => {
+      this._removeTapperById(tapperId)
+    }
+  }
+
+  /*
+   * tapImmediate(cb: Listener<V>): Untap {
+   *   const ret = this.tap(cb)
+   *   return ret
+   * }
+   */
+
+  private _removeTapperById(id: number) {
+    this._tappers.delete(id)
+    this._check()
+  }
+
+  // /**
+  //  * @deprecated
+  //  */
+  // map<T>(transform: {bivarianceHack(v: V): T}['bivarianceHack']): Tappable<T> {
+  //   return new Tappable({
+  //     tapToSource: (cb: (v: T) => void) => {
+  //       return this.tap((v: $IntentionalAny) => {
+  //         return cb(transform(v))
+  //       })
+  //     },
+  //   })
+  // }
+}

packages/dataverse/src/utils/typeTestUtils.ts

@@ -0,0 +1,12 @@
+import type {$IntentionalAny} from '../types'
+
+/**
+ * Useful in type tests, such as: const a: SomeType = _any
+ */
+export const _any: $IntentionalAny = null
+
+/**
+ * Useful in typeTests. If you want to ensure that value v follows type V,
+ * just write `expectType<V>(v)`
+ */
+export const expectType = <T extends unknown>(v: T): T => v

packages/dataverse/src/utils/updateDeep.ts

@@ -0,0 +1,42 @@
+import type {$FixMe, $IntentionalAny} from '../types'
+
+export default function updateDeep<S>(
+  state: S,
+  path: (string | number | undefined)[],
+  reducer: (...args: $IntentionalAny[]) => $IntentionalAny,
+): S {
+  if (path.length === 0) return reducer(state)
+  return hoop(state, path as $IntentionalAny, reducer)
+}
+
+const hoop = (
+  s: $FixMe,
+  path: (string | number)[],
+  reducer: $FixMe,
+): $FixMe => {
+  if (path.length === 0) {
+    return reducer(s)
+  }
+  if (Array.isArray(s)) {
+    let [index, ...restOfPath] = path
+    index = parseInt(String(index), 10)
+    if (isNaN(index)) index = 0
+    const oldVal = s[index]
+    const newVal = hoop(oldVal, restOfPath, reducer)
+    if (oldVal === newVal) return s
+    const newS = [...s]
+    newS.splice(index, 1, newVal)
+    return newS
+  } else if (typeof s === 'object' && s !== null) {
+    const [key, ...restOfPath] = path
+    const oldVal = s[key]
+    const newVal = hoop(oldVal, restOfPath, reducer)
+    if (oldVal === newVal) return s
+    const newS = {...s, [key]: newVal}
+    return newS
+  } else {
+    const [key, ...restOfPath] = path
+
+    return {[key]: hoop(undefined, restOfPath, reducer)}
+  }
+}

packages/dataverse/tsconfig.json

@@ -0,0 +1,12 @@
+{
+  "extends": "../../tsconfig.base.json",
+  "compilerOptions": {
+    "outDir": "dist",
+    "lib": ["ESNext", "DOM"],
+    "rootDir": "src",
+    "types": ["jest", "node"],
+    "emitDeclarationOnly": false,
+    "composite": true
+  },
+  "include": ["./src/**/*"]
+}

packages/dataverse2/.babelrc.js

@@ -0,0 +1 @@
+module.exports = {}

packages/dataverse2/.gitignore

@@ -0,0 +1 @@
+/dist

packages/dataverse2/LICENSE

@@ -0,0 +1,203 @@
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
+
+      "License" shall mean the terms and conditions for use, reproduction,
+      and distribution as defined by Sections 1 through 9 of this document.
+
+      "Licensor" shall mean the copyright owner or entity authorized by
+      the copyright owner that is granting the License.
+
+      "Legal Entity" shall mean the union of the acting entity and all
+      other entities that control, are controlled by, or are under common
+      control with that entity. For the purposes of this definition,
+      "control" means (i) the power, direct or indirect, to cause the
+      direction or management of such entity, whether by contract or
+      otherwise, or (ii) ownership of fifty percent (50%) or more of the
+      outstanding shares, or (iii) beneficial ownership of such entity.
+
+      "You" (or "Your") shall mean an individual or Legal Entity
+      exercising permissions granted by this License.
+
+      "Source" form shall mean the preferred form for making modifications,
+      including but not limited to software source code, documentation
+      source, and configuration files.
+
+      "Object" form shall mean any form resulting from mechanical
+      transformation or translation of a Source form, including but
+      not limited to compiled object code, generated documentation,
+      and conversions to other media types.
+
+      "Work" shall mean the work of authorship, whether in Source or
+      Object form, made available under the License, as indicated by a
+      copyright notice that is included in or attached to the work
+      (an example is provided in the Appendix below).
+
+      "Derivative Works" shall mean any work, whether in Source or Object
+      form, that is based on (or derived from) the Work and for which the
+      editorial revisions, annotations, elaborations, or other modifications
+      represent, as a whole, an original work of authorship. For the purposes
+      of this License, Derivative Works shall not include works that remain
+      separable from, or merely link (or bind by name) to the interfaces of,
+      the Work and Derivative Works thereof.
+
+      "Contribution" shall mean any work of authorship, including
+      the original version of the Work and any modifications or additions
+      to that Work or Derivative Works thereof, that is intentionally
+      submitted to Licensor for inclusion in the Work by the copyright owner
+      or by an individual or Legal Entity authorized to submit on behalf of
+      the copyright owner. For the purposes of this definition, "submitted"
+      means any form of electronic, verbal, or written communication sent
+      to the Licensor or its representatives, including but not limited to
+      communication on electronic mailing lists, source code control systems,
+      and issue tracking systems that are managed by, or on behalf of, the
+      Licensor for the purpose of discussing and improving the Work, but
+      excluding communication that is conspicuously marked or otherwise
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+
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+

packages/dataverse2/package.json

@@ -0,0 +1,27 @@
+{
+  "name": "@theatre/dataverse2",
+  "version": "1.0.0-dev",
+  "license": "Apache-2.0",
+  "author": {
+    "name": "Aria Minaei",
+    "email": "aria@theatrejs.com",
+    "url": "https://github.com/AriaMinaei"
+  },
+  "source": "src/index.ts",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "scripts": {
+    "typecheck": "yarn run _declarations:emit",
+    "_declarations:emit": "tsc --build ./tsconfig.json"
+  },
+  "devDependencies": {
+    "@types/jest": "^26.0.23",
+    "@types/lodash-es": "^4.17.4",
+    "@types/node": "^15.6.2",
+    "@types/react": "^17.0.9",
+    "typescript": "^4.3.2"
+  },
+  "dependencies": {
+    "lodash-es": "^4.17.21"
+  }
+}

packages/dataverse2/src/Atom.ts

@@ -0,0 +1,216 @@
+import get from 'lodash-es/get'
+import isPlainObject from 'lodash-es/isPlainObject'
+import last from 'lodash-es/last'
+import DerivationFromSource from './derivations/DerivationFromSource'
+import type {IDerivation} from './derivations/IDerivation'
+import {isDerivation} from './derivations/IDerivation'
+import type {Pointer, PointerType} from './pointer'
+import pointer, {getPointerMeta} from './pointer'
+import type {$FixMe, $IntentionalAny} from './types'
+import type {PathBasedReducer} from './utils/PathBasedReducer'
+import updateDeep from './utils/updateDeep'
+
+type Listener = (newVal: unknown) => void
+
+enum ValueTypes {
+  Dict,
+  Array,
+  Other,
+}
+
+const getTypeOfValue = (v: unknown): ValueTypes => {
+  if (Array.isArray(v)) return ValueTypes.Array
+  if (isPlainObject(v)) return ValueTypes.Dict
+  return ValueTypes.Other
+}
+
+const getKeyOfValue = (
+  v: unknown,
+  key: string | number,
+  vType: ValueTypes = getTypeOfValue(v),
+): unknown => {
+  if (vType === ValueTypes.Dict && typeof key === 'string') {
+    return (v as $IntentionalAny)[key]
+  } else if (vType === ValueTypes.Array && isValidArrayIndex(key)) {
+    return (v as $IntentionalAny)[key]
+  } else {
+    return undefined
+  }
+}
+
+const isValidArrayIndex = (key: string | number): boolean => {
+  const inNumber = typeof key === 'number' ? key : parseInt(key, 10)
+  return (
+    !isNaN(inNumber) &&
+    inNumber >= 0 &&
+    inNumber < Infinity &&
+    (inNumber | 0) === inNumber
+  )
+}
+
+class Scope {
+  children: Map<string | number, Scope> = new Map()
+  identityChangeListeners: Set<Listener> = new Set()
+  constructor(
+    readonly _parent: undefined | Scope,
+    readonly _path: (string | number)[],
+  ) {}
+
+  addIdentityChangeListener(cb: Listener) {
+    this.identityChangeListeners.add(cb)
+  }
+
+  removeIdentityChangeListener(cb: Listener) {
+    this.identityChangeListeners.delete(cb)
+    this._checkForGC()
+  }
+
+  removeChild(key: string | number) {
+    this.children.delete(key)
+    this._checkForGC()
+  }
+
+  getChild(key: string | number) {
+    return this.children.get(key)
+  }
+
+  getOrCreateChild(key: string | number) {
+    let child = this.children.get(key)
+    if (!child) {
+      child = child = new Scope(this, this._path.concat([key]))
+      this.children.set(key, child)
+    }
+    return child
+  }
+
+  _checkForGC() {
+    if (this.identityChangeListeners.size > 0) return
+    if (this.children.size > 0) return
+
+    if (this._parent) {
+      this._parent.removeChild(last(this._path) as string | number)
+    }
+  }
+}
+
+export default class Atom<State extends {}> {
+  private _currentState: State
+  private readonly _rootScope: Scope
+  readonly pointer: Pointer<State>
+
+  constructor(initialState: State) {
+    this._currentState = initialState
+    this._rootScope = new Scope(undefined, [])
+    this.pointer = pointer({root: this as $FixMe, path: []})
+  }
+
+  setState(newState: State) {
+    const oldState = this._currentState
+    this._currentState = newState
+
+    this._checkUpdates(this._rootScope, oldState, newState)
+  }
+
+  getState() {
+    return this._currentState
+  }
+
+  getIn(path: (string | number)[]): unknown {
+    return path.length === 0 ? this.getState() : get(this.getState(), path)
+  }
+
+  reduceState: PathBasedReducer<State, State> = (
+    path: $IntentionalAny[],
+    reducer: $IntentionalAny,
+  ) => {
+    const newState = updateDeep(this.getState(), path, reducer)
+    this.setState(newState)
+    return newState
+  }
+
+  setIn(path: $FixMe[], val: $FixMe) {
+    return this.reduceState(path, () => val)
+  }
+
+  private _checkUpdates(scope: Scope, oldState: unknown, newState: unknown) {
+    if (oldState === newState) return
+    scope.identityChangeListeners.forEach((cb) => cb(newState))
+
+    if (scope.children.size === 0) return
+    const oldValueType = getTypeOfValue(oldState)
+    const newValueType = getTypeOfValue(newState)
+
+    if (oldValueType === ValueTypes.Other && oldValueType === newValueType)
+      return
+
+    scope.children.forEach((childScope, childKey) => {
+      const oldChildVal = getKeyOfValue(oldState, childKey, oldValueType)
+      const newChildVal = getKeyOfValue(newState, childKey, newValueType)
+      this._checkUpdates(childScope, oldChildVal, newChildVal)
+    })
+  }
+
+  private _getOrCreateScopeForPath(path: (string | number)[]): Scope {
+    let curScope = this._rootScope
+    for (const pathEl of path) {
+      curScope = curScope.getOrCreateChild(pathEl)
+    }
+    return curScope
+  }
+
+  onPathValueChange(path: (string | number)[], cb: (v: unknown) => void) {
+    const scope = this._getOrCreateScopeForPath(path)
+    scope.identityChangeListeners.add(cb)
+    const untap = () => {
+      scope.identityChangeListeners.delete(cb)
+    }
+    return untap
+  }
+}
+
+const identityDerivationWeakMap = new WeakMap<{}, IDerivation<unknown>>()
+
+export const valueDerivation = <P extends PointerType<$IntentionalAny>>(
+  pointer: P,
+): IDerivation<P extends PointerType<infer T> ? T : void> => {
+  const meta = getPointerMeta(pointer)
+
+  let derivation = identityDerivationWeakMap.get(meta)
+  if (!derivation) {
+    const root = meta.root
+    if (!(root instanceof Atom)) {
+      throw new Error(
+        `Cannot run valueDerivation on a pointer whose root is not an Atom`,
+      )
+    }
+    const {path} = meta
+    derivation = new DerivationFromSource<$IntentionalAny>(
+      (listener) => root.onPathValueChange(path, listener),
+      () => root.getIn(path),
+    )
+    identityDerivationWeakMap.set(meta, derivation)
+  }
+  return derivation as $IntentionalAny
+}
+
+export const val = <P>(
+  pointerOrDerivationOrPlainValue: P,
+): P extends PointerType<infer T>
+  ? T
+  : P extends IDerivation<infer T>
+  ? T
+  : unknown => {
+  if (isPointer(pointerOrDerivationOrPlainValue)) {
+    return valueDerivation(
+      pointerOrDerivationOrPlainValue,
+    ).getValue() as $IntentionalAny
+  } else if (isDerivation(pointerOrDerivationOrPlainValue)) {
+    return pointerOrDerivationOrPlainValue.getValue() as $IntentionalAny
+  } else {
+    return pointerOrDerivationOrPlainValue as $IntentionalAny
+  }
+}
+
+export const isPointer = (p: $IntentionalAny): p is Pointer<unknown> => {
+  return p && p.$pointerMeta ? true : false
+}

packages/dataverse2/src/Box.ts

@@ -0,0 +1,33 @@
+import DerivationFromSource from './derivations/DerivationFromSource'
+import type {IDerivation} from './derivations/IDerivation'
+import Emitter from './utils/Emitter'
+export interface IBox<V> {
+  set(v: V): void
+  get(): V
+  derivation: IDerivation<V>
+}
+
+export default class Box<V> implements IBox<V> {
+  private _publicDerivation: IDerivation<V>
+  private _emitter = new Emitter<V>()
+
+  constructor(protected _value: V) {
+    this._publicDerivation = new DerivationFromSource(
+      (listener) => this._emitter.tappable.tap(listener),
+      this.get.bind(this),
+    )
+  }
+
+  set(v: V) {
+    this._value = v
+    this._emitter.emit(v)
+  }
+
+  get() {
+    return this._value
+  }
+
+  get derivation() {
+    return this._publicDerivation
+  }
+}

packages/dataverse2/src/Ticker.ts

@@ -0,0 +1,84 @@
+type ICallback = (t: number) => void
+
+export default class Ticker {
+  private _scheduledForThisOrNextTick: Set<ICallback>
+  private _scheduledForNextTick: Set<ICallback>
+  private _timeAtCurrentTick: number
+  private _ticking: boolean = false
+
+  constructor() {
+    this._scheduledForThisOrNextTick = new Set()
+    this._scheduledForNextTick = new Set()
+    this._timeAtCurrentTick = 0
+  }
+
+  /**
+   * Registers for fn to be called either on this tick or the next tick.
+   *
+   * If registerSideEffect() is called while Ticker.tick() is running, the
+   * side effect _will_ be called within the running tick. If you don't want this
+   * behavior, you can use registerSideEffectForNextTick().
+   *
+   * Note that fn will be added to a Set(). Which means, if you call registerSideEffect(fn)
+   * with the same fn twice in a single tick, it'll only run once.
+   */
+  onThisOrNextTick(fn: ICallback) {
+    this._scheduledForThisOrNextTick.add(fn)
+  }
+
+  /**
+   * Registers a side effect to be called on the next tick.
+   *
+   * @see Ticker:onThisOrNextTick()
+   */
+  onNextTick(fn: ICallback) {
+    this._scheduledForNextTick.add(fn)
+  }
+
+  offThisOrNextTick(fn: ICallback) {
+    this._scheduledForThisOrNextTick.delete(fn)
+  }
+
+  offNextTick(fn: ICallback) {
+    this._scheduledForNextTick.delete(fn)
+  }
+
+  get time() {
+    if (this._ticking) {
+      return this._timeAtCurrentTick
+    } else return performance.now()
+  }
+
+  tick(t: number = performance.now()) {
+    this._ticking = true
+    this._timeAtCurrentTick = t
+    this._scheduledForNextTick.forEach((v) =>
+      this._scheduledForThisOrNextTick.add(v),
+    )
+    this._scheduledForNextTick.clear()
+    this._tick(0)
+    this._ticking = false
+  }
+
+  private _tick(iterationNumber: number): void {
+    const time = this.time
+
+    if (iterationNumber > 10) {
+      console.warn('_tick() recursing for 10 times')
+    }
+
+    if (iterationNumber > 100) {
+      throw new Error(`Maximum recursion limit for _tick()`)
+    }
+
+    const oldSet = this._scheduledForThisOrNextTick
+    this._scheduledForThisOrNextTick = new Set()
+    oldSet.forEach((fn) => {
+      fn(time)
+    })
+
+    if (this._scheduledForThisOrNextTick.size > 0) {
+      return this._tick(iterationNumber + 1)
+    }
+  }
+}

packages/dataverse2/src/atom.typeTest.ts

@@ -0,0 +1,24 @@
+import Atom, {val} from './Atom'
+import {expectType, _any} from './utils/typeTestUtils'
+;() => {
+  const p = new Atom<{foo: string; bar: number; optional?: boolean}>(_any)
+    .pointer
+  expectType<string>(val(p.foo))
+  // @ts-expect-error TypeTest
+  expectType<number>(val(p.foo))
+
+  expectType<number>(val(p.bar))
+  // @ts-expect-error TypeTest
+  expectType<string>(val(p.bar))
+
+  // @ts-expect-error TypeTest
+  expectType<{}>(val(p.nonExistent))
+
+  expectType<undefined | boolean>(val(p.optional))
+  // @ts-expect-error TypeTest
+  expectType<boolean>(val(p.optional))
+  // @ts-expect-error TypeTest
+  expectType<undefined>(val(p.optional))
+  // @ts-expect-error TypeTest
+  expectType<undefined | string>(val(p.optional))
+}

packages/dataverse2/src/derivations/AbstractDerivation.ts

@@ -0,0 +1,199 @@
+import type {$IntentionalAny} from '../types'
+import type Tappable from '../utils/Tappable'
+import DerivationEmitter from './DerivationEmitter'
+import flatMap from './flatMap'
+import type {GraphNode, IDerivation} from './IDerivation'
+import map from './map'
+import {
+  reportResolutionEnd,
+  reportResolutionStart,
+} from './prism/discoveryMechanism'
+
+export default abstract class AbstractDerivation<V> implements IDerivation<V> {
+  readonly isDerivation: true = true
+  private _didMarkDependentsAsStale: boolean = false
+  private _isHot: boolean = false
+
+  private _isFresh: boolean = false
+  protected _lastValue: undefined | V = undefined
+
+  protected _dependents: Set<GraphNode> = new Set()
+  protected _dependencies: Set<IDerivation<$IntentionalAny>> = new Set()
+  /**
+   * _height is the maximum height of all dependents, plus one.
+   *
+   * -1 means it's not yet calculated
+   * 0 is reserved only for listeners
+   */
+  private _height: number = -1
+
+  private _graphNode: GraphNode
+
+  protected abstract _recalculate(): V
+  protected abstract _reactToDependencyBecomingStale(
+    which: IDerivation<unknown>,
+  ): void
+
+  constructor() {
+    const self = this
+    this._graphNode = {
+      get height() {
+        return self._height
+      },
+      recalculate() {
+        // @todo
+      },
+    }
+  }
+
+  get isHot(): boolean {
+    return this._isHot
+  }
+
+  get height() {
+    return this._height
+  }
+
+  protected _addDependency(d: IDerivation<$IntentionalAny>) {
+    if (this._dependencies.has(d)) return
+    this._dependencies.add(d)
+    if (this._isHot) d.addDependent(this._graphNode)
+  }
+
+  protected _removeDependency(d: IDerivation<$IntentionalAny>) {
+    if (!this._dependencies.has(d)) return
+    this._dependencies.delete(d)
+    if (this._isHot) d.removeDependent(this._graphNode)
+  }
+
+  changes(): Tappable<V> {
+    return new DerivationEmitter(this).tappable()
+  }
+
+  addDependent(d: GraphNode) {
+    const hadDepsBefore = this._dependents.size > 0
+    this._dependents.add(d)
+
+    if (d.height > this._height - 1) {
+      this._setHeight(d.height + 1)
+    }
+
+    if (!hadDepsBefore) {
+      this._reactToNumberOfDependentsChange()
+    }
+  }
+
+  /**
+   * @sealed
+   */
+  removeDependent(d: GraphNode) {
+    const hadDepsBefore = this._dependents.size > 0
+    this._dependents.delete(d)
+    const hasDepsNow = this._dependents.size > 0
+    if (hadDepsBefore !== hasDepsNow) {
+      this._reactToNumberOfDependentsChange()
+    }
+  }
+
+  reportDependentHeightChange(d: GraphNode) {
+    if (process.env.NODE_ENV === 'development') {
+      if (!this._dependents.has(d)) {
+        throw new Error(
+          `Got a reportDependentHeightChange from a non-dependent.`,
+        )
+      }
+    }
+    this._recalculateHeight()
+  }
+
+  private _recalculateHeight() {
+    let maxHeightOfDependents = -1
+    this._dependents.forEach((d) => {
+      maxHeightOfDependents = Math.max(maxHeightOfDependents, d.height)
+    })
+    const newHeight = maxHeightOfDependents + 1
+    if (this._height !== newHeight) {
+      this._setHeight(newHeight)
+    }
+  }
+
+  private _setHeight(h: number) {
+    this._height = h
+    this._dependencies.forEach((d) => {
+      d.reportDependentHeightChange(this._graphNode)
+    })
+  }
+
+  /**
+   * This is meant to be called by subclasses
+   *
+   * @sealed
+   */
+  protected _markAsStale(which: IDerivation<$IntentionalAny>) {
+    this._internal_markAsStale(which)
+  }
+
+  private _internal_markAsStale = (which: IDerivation<$IntentionalAny>) => {
+    this._reactToDependencyBecomingStale(which)
+
+    if (this._didMarkDependentsAsStale) return
+
+    this._didMarkDependentsAsStale = true
+    this._isFresh = false
+
+    this._dependents.forEach((dependent) => {
+      dependent.recalculate()
+    })
+  }
+
+  getValue(): V {
+    reportResolutionStart(this)
+
+    if (!this._isFresh) {
+      const newValue = this._recalculate()
+      this._lastValue = newValue
+      if (this.isHot) {
+        this._isFresh = true
+        this._didMarkDependentsAsStale = false
+      }
+    }
+
+    reportResolutionEnd(this)
+    return this._lastValue!
+  }
+
+  private _reactToNumberOfDependentsChange() {
+    const shouldBecomeHot = this._dependents.size > 0
+
+    if (shouldBecomeHot === this._isHot) return
+
+    this._isHot = shouldBecomeHot
+    this._didMarkDependentsAsStale = false
+    this._isFresh = false
+    if (shouldBecomeHot) {
+      this._dependencies.forEach((d) => {
+        d.addDependent(this._graphNode)
+      })
+      this._keepHot()
+    } else {
+      this._dependencies.forEach((d) => {
+        d.removeDependent(this._graphNode)
+      })
+      this._becomeCold()
+    }
+  }
+
+  protected _keepHot() {}
+
+  protected _becomeCold() {}
+
+  map<T>(fn: (v: V) => T): IDerivation<T> {
+    return map(this, fn)
+  }
+
+  flatMap<R>(
+    fn: (v: V) => R,
+  ): IDerivation<R extends IDerivation<infer T> ? T : R> {
+    return flatMap(this, fn)
+  }
+}

packages/dataverse2/src/derivations/AbstractDerivation.typeTest.ts

@@ -0,0 +1,36 @@
+import type {$IntentionalAny} from '../types'
+import type {IDerivation} from './IDerivation'
+
+const _any: $IntentionalAny = null
+
+// map
+;() => {
+  const a: IDerivation<string> = _any
+
+  // $ExpectType IDerivation<number>
+  // eslint-disable-next-line unused-imports/no-unused-vars-ts
+  a.map((s: string) => 10)
+
+  // @ts-expect-error
+  // eslint-disable-next-line unused-imports/no-unused-vars-ts
+  a.map((s: number) => 10)
+}
+
+// flatMap()
+/* eslint-disable unused-imports/no-unused-vars-ts */
+;() => {
+  const a: IDerivation<string> = _any
+
+  // okay
+  a.flatMap((s: string) => {})
+
+  // @ts-expect-error TypeTest
+  a.flatMap((s: number) => {})
+
+  // $ExpectType IDerivation<number>
+  a.flatMap((s): IDerivation<number> => _any)
+
+  // $ExpectType IDerivation<number>
+  a.flatMap((s): number => _any)
+}
+/* eslint-enable unused-imports/no-unused-vars-ts */

packages/dataverse2/src/derivations/ConstantDerivation.ts

@@ -0,0 +1,17 @@
+import AbstractDerivation from './AbstractDerivation'
+
+export default class ConstantDerivation<V> extends AbstractDerivation<V> {
+  _v: V
+
+  constructor(v: V) {
+    super()
+    this._v = v
+    return this
+  }
+
+  _recalculate() {
+    return this._v
+  }
+
+  _reactToDependencyBecomingStale() {}
+}

packages/dataverse2/src/derivations/DerivationEmitter.ts

@@ -0,0 +1,52 @@
+import Emitter from '../utils/Emitter'
+import type {default as Tappable} from '../utils/Tappable'
+import type {GraphNode, IDerivation} from './IDerivation'
+
+export default class DerivationEmitter<V> {
+  private _emitter: Emitter<V>
+  private _lastValue: undefined | V
+  private _lastValueRecorded: boolean
+  private _hadTappers: boolean
+  private _graphNode: GraphNode
+
+  constructor(private readonly _derivation: IDerivation<V>) {
+    this._emitter = new Emitter()
+    this._graphNode = {
+      height: 0,
+      recalculate: () => {
+        this._emit()
+      },
+    }
+    this._emitter.onNumberOfTappersChange(() => {
+      this._reactToNumberOfTappersChange()
+    })
+    this._hadTappers = false
+    this._lastValueRecorded = false
+    this._lastValue = undefined
+    return this
+  }
+
+  private _reactToNumberOfTappersChange() {
+    const hasTappers = this._emitter.hasTappers()
+    if (hasTappers !== this._hadTappers) {
+      this._hadTappers = hasTappers
+      if (hasTappers) {
+        this._derivation.addDependent(this._graphNode)
+      } else {
+        this._derivation.removeDependent(this._graphNode)
+      }
+    }
+  }
+
+  tappable(): Tappable<V> {
+    return this._emitter.tappable
+  }
+
+  private _emit = () => {
+    const newValue = this._derivation.getValue()
+    if (newValue === this._lastValue && this._lastValueRecorded === true) return
+    this._lastValue = newValue
+    this._lastValueRecorded = true
+    this._emitter.emit(newValue)
+  }
+}

packages/dataverse2/src/derivations/DerivationFromSource.ts

@@ -0,0 +1,53 @@
+import type {VoidFn} from '../types'
+import AbstractDerivation from './AbstractDerivation'
+
+const noop = () => {}
+
+export default class DerivationFromSource<V> extends AbstractDerivation<V> {
+  private _untapFromChanges: () => void
+  private _cachedValue: undefined | V
+  private _hasCachedValue: boolean
+
+  constructor(
+    private readonly _tapToSource: (listener: (newValue: V) => void) => VoidFn,
+    private readonly _getValueFromSource: () => V,
+  ) {
+    super()
+    this._untapFromChanges = noop
+    this._cachedValue = undefined
+    this._hasCachedValue = false
+  }
+
+  _recalculate() {
+    if (this.isHot) {
+      if (!this._hasCachedValue) {
+        this._cachedValue = this._getValueFromSource()
+        this._hasCachedValue = true
+      }
+      return this._cachedValue as V
+    } else {
+      return this._getValueFromSource()
+    }
+  }
+
+  _keepHot() {
+    this._hasCachedValue = false
+    this._cachedValue = undefined
+
+    this._untapFromChanges = this._tapToSource((newValue) => {
+      this._hasCachedValue = true
+      this._cachedValue = newValue
+      this._markAsStale(this)
+    })
+  }
+
+  _becomeCold() {
+    this._untapFromChanges()
+    this._untapFromChanges = noop
+
+    this._hasCachedValue = false
+    this._cachedValue = undefined
+  }
+
+  _reactToDependencyBecomingStale() {}
+}

packages/dataverse2/src/derivations/Freshener.ts

@@ -0,0 +1,5 @@
+import type {GraphNode} from './IDerivation'
+
+export default class Freshener {
+  schedulePeak(d: GraphNode) {}
+}

packages/dataverse2/src/derivations/IDerivation.ts

@@ -0,0 +1,29 @@
+import type Tappable from '../utils/Tappable'
+
+export type GraphNode = {
+  height: number
+  recalculate(): void
+}
+
+export interface IDerivation<V> {
+  isDerivation: true
+  isHot: boolean
+  changes(): Tappable<V>
+
+  addDependent(d: GraphNode): void
+  removeDependent(d: GraphNode): void
+
+  reportDependentHeightChange(d: GraphNode): void
+
+  getValue(): V
+
+  map<T>(fn: (v: V) => T): IDerivation<T>
+
+  flatMap<R>(
+    fn: (v: V) => R,
+  ): IDerivation<R extends IDerivation<infer T> ? T : R>
+}
+
+export function isDerivation(d: any): d is IDerivation<unknown> {
+  return d && d.isDerivation && d.isDerivation === true
+}

packages/dataverse2/src/derivations/flatMap.ts

@@ -0,0 +1,127 @@
+import type {$FixMe} from '../types'
+import AbstractDerivation from './AbstractDerivation'
+import type {IDerivation} from './IDerivation'
+
+enum UPDATE_NEEDED_FROM {
+  none = 0,
+  dep = 1,
+  inner = 2,
+}
+
+const makeFlatMapDerivationClass = () => {
+  class FlatMapDerivation<V, DepType> extends AbstractDerivation<V> {
+    private _innerDerivation: undefined | null | IDerivation<V>
+    private _staleDependency: UPDATE_NEEDED_FROM
+
+    static displayName = 'flatMap'
+
+    constructor(
+      readonly _depDerivation: IDerivation<DepType>,
+      readonly _fn: (v: DepType) => IDerivation<V> | V,
+    ) {
+      super()
+      this._innerDerivation = undefined
+      this._staleDependency = UPDATE_NEEDED_FROM.dep
+
+      this._addDependency(_depDerivation)
+
+      return this
+    }
+
+    _recalculateHot() {
+      const updateNeededFrom = this._staleDependency
+      this._staleDependency = UPDATE_NEEDED_FROM.none
+
+      if (updateNeededFrom === UPDATE_NEEDED_FROM.inner) {
+        // @ts-ignore
+        return this._innerDerivation.getValue()
+      }
+
+      const possibleInnerDerivation = this._fn(this._depDerivation.getValue())
+
+      if (possibleInnerDerivation instanceof AbstractDerivation) {
+        this._innerDerivation = possibleInnerDerivation
+        this._addDependency(possibleInnerDerivation)
+        return possibleInnerDerivation.getValue()
+      } else {
+        return possibleInnerDerivation
+      }
+    }
+
+    protected _recalculateCold() {
+      const possibleInnerDerivation = this._fn(this._depDerivation.getValue())
+
+      if (possibleInnerDerivation instanceof AbstractDerivation) {
+        return possibleInnerDerivation.getValue()
+      } else {
+        return possibleInnerDerivation
+      }
+    }
+
+    protected _recalculate() {
+      return this.isHot ? this._recalculateHot() : this._recalculateCold()
+    }
+
+    protected _reactToDependencyBecomingStale(
+      msgComingFrom: IDerivation<unknown>,
+    ) {
+      const updateNeededFrom =
+        msgComingFrom === this._depDerivation
+          ? UPDATE_NEEDED_FROM.dep
+          : UPDATE_NEEDED_FROM.inner
+
+      if (
+        updateNeededFrom === UPDATE_NEEDED_FROM.inner &&
+        msgComingFrom !== this._innerDerivation
+      ) {
+        throw Error(
+          `got a _pipostale() from neither the dep nor the inner derivation`,
+        )
+      }
+
+      if (this._staleDependency === UPDATE_NEEDED_FROM.none) {
+        this._staleDependency = updateNeededFrom
+
+        if (updateNeededFrom === UPDATE_NEEDED_FROM.dep) {
+          this._removeInnerDerivation()
+        }
+      } else if (this._staleDependency === UPDATE_NEEDED_FROM.dep) {
+      } else {
+        if (updateNeededFrom === UPDATE_NEEDED_FROM.dep) {
+          this._staleDependency = UPDATE_NEEDED_FROM.dep
+          this._removeInnerDerivation()
+        }
+      }
+    }
+
+    private _removeInnerDerivation() {
+      if (this._innerDerivation) {
+        this._removeDependency(this._innerDerivation)
+        this._innerDerivation = undefined
+      }
+    }
+
+    protected _keepHot() {
+      this._staleDependency = UPDATE_NEEDED_FROM.dep
+      this.getValue()
+    }
+
+    protected _becomeCold() {
+      this._staleDependency = UPDATE_NEEDED_FROM.dep
+      this._removeInnerDerivation()
+    }
+  }
+  return FlatMapDerivation
+}
+
+let cls: ReturnType<typeof makeFlatMapDerivationClass> | undefined = undefined
+
+export default function flatMap<V, R>(
+  dep: IDerivation<V>,
+  fn: (v: V) => R,
+): IDerivation<R extends IDerivation<infer T> ? T : R> {
+  if (!cls) {
+    cls = makeFlatMapDerivationClass()
+  }
+  return new cls(dep, fn) as $FixMe
+}

packages/dataverse2/src/derivations/iterateAndCountTicks.ts

@@ -0,0 +1,32 @@
+import {isPointer, valueDerivation} from '../Atom'
+import type {Pointer} from '../pointer'
+import type {IDerivation} from './IDerivation'
+import {isDerivation} from './IDerivation'
+
+export default function* iterateAndCountTicks<V>(
+  pointerOrDerivation: IDerivation<V> | Pointer<V>,
+): Generator<{value: V; ticks: number}, void, void> {
+  let d
+  if (isPointer(pointerOrDerivation)) {
+    d = valueDerivation(pointerOrDerivation) as IDerivation<V>
+  } else if (isDerivation(pointerOrDerivation)) {
+    d = pointerOrDerivation
+  } else {
+    throw new Error(`Only pointers and derivations are supported`)
+  }
+
+  let ticksCountedSinceLastYield = 0
+  const untap = d.changes().tap(() => {
+    ticksCountedSinceLastYield++
+  })
+
+  try {
+    while (true) {
+      const ticks = ticksCountedSinceLastYield
+      ticksCountedSinceLastYield = 0
+      yield {value: d.getValue(), ticks}
+    }
+  } finally {
+    untap()
+  }
+}

packages/dataverse2/src/derivations/iterateOver.test.ts

@@ -0,0 +1,19 @@
+import Atom from '../Atom'
+import iterateOver from './iterateOver'
+
+describe.skip(`iterateOver()`, () => {
+  test('it should work', () => {
+    const a = new Atom({a: 0})
+    let iter = iterateOver(a.pointer.a)
+    expect(iter.next().value).toEqual(0)
+    a.setIn(['a'], 1)
+    a.setIn(['a'], 2)
+    expect(iter.next()).toMatchObject({value: 2, done: false})
+    iter.return()
+    iter = iterateOver(a.pointer.a)
+    expect(iter.next().value).toEqual(2)
+    a.setIn(['a'], 3)
+    expect(iter.next()).toMatchObject({done: false, value: 3})
+    iter.return()
+  })
+})

packages/dataverse2/src/derivations/iterateOver.ts

@@ -0,0 +1,32 @@
+import {isPointer, valueDerivation} from '../Atom'
+import type {Pointer} from '../pointer'
+import Ticker from '../Ticker'
+import type {IDerivation} from './IDerivation'
+import {isDerivation} from './IDerivation'
+
+export default function* iterateOver<V>(
+  pointerOrDerivation: IDerivation<V> | Pointer<V>,
+): Generator<V, void, void> {
+  let d
+  if (isPointer(pointerOrDerivation)) {
+    d = valueDerivation(pointerOrDerivation) as IDerivation<V>
+  } else if (isDerivation(pointerOrDerivation)) {
+    d = pointerOrDerivation
+  } else {
+    throw new Error(`Only pointers and derivations are supported`)
+  }
+
+  const ticker = new Ticker()
+
+  const untap = d.changes().tap((v) => {})
+
+  try {
+    while (true) {
+      ticker.tick()
+
+      yield d.getValue()
+    }
+  } finally {
+    untap()
+  }
+}

packages/dataverse2/src/derivations/map.ts

@@ -0,0 +1,32 @@
+import AbstractDerivation from './AbstractDerivation'
+import type {IDerivation} from './IDerivation'
+
+// Exporting from a function because of the circular dependency with AbstractDerivation
+const makeMapDerivationClass = () =>
+  class MapDerivation<T, V> extends AbstractDerivation<V> {
+    constructor(
+      private readonly _dep: IDerivation<T>,
+      private readonly _fn: (t: T) => V,
+    ) {
+      super()
+      this._addDependency(_dep)
+    }
+
+    _recalculate() {
+      return this._fn(this._dep.getValue())
+    }
+
+    _reactToDependencyBecomingStale() {}
+  }
+
+let cls: ReturnType<typeof makeMapDerivationClass> | undefined = undefined
+
+export default function flatMap<V, R>(
+  dep: IDerivation<V>,
+  fn: (v: V) => R,
+): IDerivation<R> {
+  if (!cls) {
+    cls = makeMapDerivationClass()
+  }
+  return new cls(dep, fn)
+}

packages/dataverse2/src/derivations/prism/discoveryMechanism.ts

@@ -0,0 +1,50 @@
+import type {$IntentionalAny} from '../../types'
+import Stack from '../../utils/Stack'
+import type {IDerivation} from '../IDerivation'
+
+const noop = () => {}
+
+const stack = new Stack<Collector>()
+const noopCollector: Collector = noop
+
+type Collector = (d: IDerivation<$IntentionalAny>) => void
+
+export const collectObservedDependencies = (
+  cb: () => void,
+  collector: Collector,
+) => {
+  stack.push(collector)
+  cb()
+  stack.pop()
+}
+
+export const startIgnoringDependencies = () => {
+  stack.push(noopCollector)
+}
+
+export const stopIgnoringDependencies = () => {
+  if (stack.peek() !== noopCollector) {
+    if (process.env.NODE_ENV === 'development') {
+      console.warn('This should never happen')
+    }
+  } else {
+    stack.pop()
+  }
+}
+
+export const reportResolutionStart = (d: IDerivation<$IntentionalAny>) => {
+  const possibleCollector = stack.peek()
+  if (possibleCollector) {
+    possibleCollector(d)
+  }
+
+  stack.push(noopCollector)
+}
+
+export const reportResolutionEnd = (_d: IDerivation<$IntentionalAny>) => {
+  stack.pop()
+}
+
+export const isCollectingDependencies = () => {
+  return stack.peek() !== noopCollector
+}

packages/dataverse2/src/derivations/prism/prism.test.ts

@@ -0,0 +1,225 @@
+import Atom, {val} from '../../Atom'
+import Ticker from '../../Ticker'
+import type {$FixMe, $IntentionalAny} from '../../types'
+import ConstantDerivation from '../ConstantDerivation'
+import iterateAndCountTicks from '../iterateAndCountTicks'
+import prism, {PrismDerivation} from './prism'
+
+describe.skip('prism', () => {
+  let ticker: Ticker
+  beforeEach(() => {
+    ticker = new Ticker()
+  })
+
+  it('should work', () => {
+    const o = new Atom({foo: 'foo'})
+    const d = new PrismDerivation(() => {
+      return val(o.pointer.foo) + 'boo'
+    })
+    expect(d.getValue()).toEqual('fooboo')
+
+    const changes: Array<$FixMe> = []
+    d.changes().tap((c) => {
+      changes.push(c)
+    })
+
+    o.reduceState(['foo'], () => 'foo2')
+    ticker.tick()
+    expect(changes).toMatchObject(['foo2boo'])
+  })
+  it('should only collect immediate dependencies', () => {
+    const aD = new ConstantDerivation(1)
+    const bD = aD.map((v) => v * 2)
+    const cD = prism(() => {
+      return bD.getValue()
+    })
+    expect(cD.getValue()).toEqual(2)
+    expect((cD as $IntentionalAny)._dependencies.size).toEqual(1)
+  })
+
+  describe('prism.ref()', () => {
+    it('should work', () => {
+      const theAtom: Atom<{n: number}> = new Atom({n: 2})
+
+      const isEvenD = prism((): {isEven: boolean} => {
+        const ref = prism.ref<{isEven: boolean} | undefined>('cache', undefined)
+        const currentN = val(theAtom.pointer.n)
+
+        const isEven = currentN % 2 === 0
+        if (ref.current && ref.current.isEven === isEven) {
+          return ref.current
+        } else {
+          ref.current = {isEven}
+          return ref.current
+        }
+      })
+
+      const iterator = iterateAndCountTicks(isEvenD)
+
+      theAtom.reduceState(['n'], () => 3)
+
+      expect(iterator.next().value).toMatchObject({
+        value: {isEven: false},
+        ticks: 0,
+      })
+      theAtom.reduceState(['n'], () => 5)
+      theAtom.reduceState(['n'], () => 7)
+      expect(iterator.next().value).toMatchObject({
+        value: {isEven: false},
+        ticks: 1,
+      })
+      theAtom.reduceState(['n'], () => 2)
+      theAtom.reduceState(['n'], () => 4)
+      expect(iterator.next().value).toMatchObject({
+        value: {isEven: true},
+        ticks: 1,
+      })
+      expect(iterator.next().value).toMatchObject({
+        value: {isEven: true},
+        ticks: 0,
+      })
+    })
+  })
+
+  describe('prism.effect()', () => {
+    it('should work', async () => {
+      let iteration = 0
+      const sequence: unknown[] = []
+      let deps: unknown[] = []
+
+      const a = new Atom({letter: 'a'})
+
+      const derivation = prism(() => {
+        const n = val(a.pointer.letter)
+        const iterationAtTimeOfCall = iteration
+        sequence.push({derivationCall: iterationAtTimeOfCall})
+
+        prism.effect(
+          'f',
+          () => {
+            sequence.push({effectCall: iterationAtTimeOfCall})
+            return () => {
+              sequence.push({cleanupCall: iterationAtTimeOfCall})
+            }
+          },
+          [...deps],
+        )
+
+        return n
+      })
+
+      const untap = derivation.changes().tap((change) => {
+        sequence.push({change})
+      })
+
+      expect(sequence).toMatchObject([{derivationCall: 0}, {effectCall: 0}])
+      sequence.length = 0
+
+      iteration++
+      a.setIn(['letter'], 'b')
+      ticker.tick()
+      expect(sequence).toMatchObject([{derivationCall: 1}, {change: 'b'}])
+      sequence.length = 0
+
+      deps = [1]
+      iteration++
+      a.setIn(['letter'], 'c')
+      ticker.tick()
+      expect(sequence).toMatchObject([
+        {derivationCall: 2},
+        {cleanupCall: 0},
+        {effectCall: 2},
+        {change: 'c'},
+      ])
+      sequence.length = 0
+
+      untap()
+
+      // takes a tick before untap takes effect
+      await new Promise((resolve) => setTimeout(resolve, 1))
+      expect(sequence).toMatchObject([{cleanupCall: 2}])
+    })
+  })
+
+  describe('prism.memo()', () => {
+    it('should work', async () => {
+      let iteration = 0
+      const sequence: unknown[] = []
+      let deps: unknown[] = []
+
+      const a = new Atom({letter: 'a'})
+
+      const derivation = prism(() => {
+        const n = val(a.pointer.letter)
+        const iterationAtTimeOfCall = iteration
+        sequence.push({derivationCall: iterationAtTimeOfCall})
+
+        const resultOfMemo = prism.memo(
+          'memo',
+          () => {
+            sequence.push({memoCall: iterationAtTimeOfCall})
+            return iterationAtTimeOfCall
+          },
+          [...deps],
+        )
+
+        sequence.push({resultOfMemo})
+
+        return n
+      })
+
+      const untap = derivation.changes().tap((change) => {
+        sequence.push({change})
+      })
+
+      expect(sequence).toMatchObject([
+        {derivationCall: 0},
+        {memoCall: 0},
+        {resultOfMemo: 0},
+      ])
+      sequence.length = 0
+
+      iteration++
+      a.setIn(['letter'], 'b')
+      ticker.tick()
+      expect(sequence).toMatchObject([
+        {derivationCall: 1},
+        {resultOfMemo: 0},
+        {change: 'b'},
+      ])
+      sequence.length = 0
+
+      deps = [1]
+      iteration++
+      a.setIn(['letter'], 'c')
+      ticker.tick()
+      expect(sequence).toMatchObject([
+        {derivationCall: 2},
+        {memoCall: 2},
+        {resultOfMemo: 2},
+        {change: 'c'},
+      ])
+      sequence.length = 0
+
+      untap()
+    })
+  })
+
+  describe(`prism.scope()`, () => {
+    it('should prevent name conflicts', () => {
+      const d = prism(() => {
+        const thisNameWillBeUsedForBothMemos = 'blah'
+        const a = prism.scope('a', () => {
+          return prism.memo(thisNameWillBeUsedForBothMemos, () => 'a', [])
+        })
+
+        const b = prism.scope('b', () => {
+          return prism.memo(thisNameWillBeUsedForBothMemos, () => 'b', [])
+        })
+
+        return {a, b}
+      })
+      expect(d.getValue()).toMatchObject({a: 'a', b: 'b'})
+    })
+  })
+})

packages/dataverse2/src/derivations/prism/prism.ts

@@ -0,0 +1,331 @@
+import Box from '../../Box'
+import type {$IntentionalAny, VoidFn} from '../../types'
+import Stack from '../../utils/Stack'
+import AbstractDerivation from '../AbstractDerivation'
+import type {IDerivation} from '../IDerivation'
+import {
+  collectObservedDependencies,
+  startIgnoringDependencies,
+  stopIgnoringDependencies,
+} from './discoveryMechanism'
+
+const voidFn = () => {}
+
+export class PrismDerivation<V> extends AbstractDerivation<V> {
+  protected _cacheOfDendencyValues: Map<IDerivation<unknown>, unknown> =
+    new Map()
+  protected _possiblyStaleDeps = new Set<IDerivation<unknown>>()
+  private _prismScope = new PrismScope()
+
+  constructor(readonly _fn: () => V) {
+    super()
+  }
+
+  _recalculate() {
+    let value: V
+
+    if (this._possiblyStaleDeps.size > 0) {
+      let anActuallyStaleDepWasFound = false
+      startIgnoringDependencies()
+      for (const dep of this._possiblyStaleDeps) {
+        if (this._cacheOfDendencyValues.get(dep) !== dep.getValue()) {
+          anActuallyStaleDepWasFound = true
+          break
+        }
+      }
+      stopIgnoringDependencies()
+      this._possiblyStaleDeps.clear()
+      if (!anActuallyStaleDepWasFound) {
+        // console.log('ok')
+
+        return this._lastValue!
+      }
+    }
+
+    const newDeps: Set<IDerivation<unknown>> = new Set()
+    this._cacheOfDendencyValues.clear()
+    collectObservedDependencies(
+      () => {
+        hookScopeStack.push(this._prismScope)
+        try {
+          value = this._fn()
+        } catch (error) {
+          console.error(error)
+        } finally {
+          const topOfTheStack = hookScopeStack.pop()
+          if (topOfTheStack !== this._prismScope) {
+            console.warn(
+              // @todo guide the user to report the bug in an issue
+              `The Prism hook stack has slipped. This is a bug.`,
+            )
+          }
+        }
+      },
+      (observedDep) => {
+        newDeps.add(observedDep)
+        this._addDependency(observedDep)
+      },
+    )
+
+    this._dependencies.forEach((dep) => {
+      if (!newDeps.has(dep)) {
+        this._removeDependency(dep)
+      }
+    })
+
+    this._dependencies = newDeps
+
+    startIgnoringDependencies()
+    newDeps.forEach((dep) => {
+      this._cacheOfDendencyValues.set(dep, dep.getValue())
+    })
+    stopIgnoringDependencies()
+
+    return value!
+  }
+
+  _reactToDependencyBecomingStale(msgComingFrom: IDerivation<unknown>) {
+    this._possiblyStaleDeps.add(msgComingFrom)
+  }
+
+  _keepHot() {
+    this._prismScope = new PrismScope()
+    startIgnoringDependencies()
+    this.getValue()
+    stopIgnoringDependencies()
+  }
+
+  _becomeCold() {
+    cleanupScopeStack(this._prismScope)
+    this._prismScope = new PrismScope()
+  }
+}
+
+class PrismScope {
+  isPrismScope = true
+  private _subs: Record<string, PrismScope> = {}
+
+  sub(key: string) {
+    if (!this._subs[key]) {
+      this._subs[key] = new PrismScope()
+    }
+    return this._subs[key]
+  }
+
+  get subs() {
+    return this._subs
+  }
+}
+
+function cleanupScopeStack(scope: PrismScope) {
+  for (const [_, sub] of Object.entries(scope.subs)) {
+    cleanupScopeStack(sub)
+  }
+  cleanupEffects(scope)
+}
+
+function cleanupEffects(scope: PrismScope) {
+  const effects = effectsWeakMap.get(scope)
+  if (effects) {
+    for (const k of Object.keys(effects)) {
+      const effect = effects[k]
+      safelyRun(effect.cleanup, undefined)
+    }
+  }
+  effectsWeakMap.delete(scope)
+}
+
+function safelyRun<T, U>(
+  fn: () => T,
+  returnValueInCaseOfError: U,
+): {success: boolean; returnValue: T | U} {
+  let returnValue: T | U = returnValueInCaseOfError
+  let success = false
+  try {
+    returnValue = fn()
+    success = true
+  } catch (error) {
+    setTimeout(() => {
+      throw error
+    })
+  }
+  return {success, returnValue}
+}
+
+const hookScopeStack = new Stack<PrismScope>()
+
+const refsWeakMap = new WeakMap<PrismScope, Record<string, IRef<unknown>>>()
+
+type IRef<T> = {
+  current: T
+}
+const effectsWeakMap = new WeakMap<PrismScope, Record<string, IEffect>>()
+
+type IEffect = {
+  deps: undefined | unknown[]
+  cleanup: VoidFn
+}
+
+const memosWeakMap = new WeakMap<PrismScope, Record<string, IMemo>>()
+
+type IMemo = {
+  deps: undefined | unknown[]
+  cachedValue: unknown
+}
+
+function ref<T>(key: string, initialValue: T): IRef<T> {
+  const scope = hookScopeStack.peek()
+  if (!scope) {
+    throw new Error(`prism.ref() is called outside of a prism() call.`)
+  }
+  let refs = refsWeakMap.get(scope)
+  if (!refs) {
+    refs = {}
+    refsWeakMap.set(scope, refs)
+  }
+
+  if (refs[key]) {
+    return refs[key] as $IntentionalAny as IRef<T>
+  } else {
+    const ref: IRef<T> = {
+      current: initialValue,
+    }
+    refs[key] = ref
+    return ref
+  }
+}
+
+function effect(key: string, cb: () => () => void, deps?: unknown[]): void {
+  const scope = hookScopeStack.peek()
+  if (!scope) {
+    throw new Error(`prism.effect() is called outside of a prism() call.`)
+  }
+  let effects = effectsWeakMap.get(scope)
+
+  if (!effects) {
+    effects = {}
+    effectsWeakMap.set(scope, effects)
+  }
+
+  if (!effects[key]) {
+    effects[key] = {
+      cleanup: voidFn,
+      deps: [{}],
+    }
+  }
+
+  const effect = effects[key]
+  if (depsHaveChanged(effect.deps, deps)) {
+    effect.cleanup()
+
+    startIgnoringDependencies()
+    effect.cleanup = safelyRun(cb, voidFn).returnValue
+    stopIgnoringDependencies()
+    effect.deps = deps
+  }
+}
+
+function depsHaveChanged(
+  oldDeps: undefined | unknown[],
+  newDeps: undefined | unknown[],
+): boolean {
+  if (oldDeps === undefined || newDeps === undefined) {
+    return true
+  } else if (oldDeps.length !== newDeps.length) {
+    return true
+  } else {
+    return oldDeps.some((el, i) => el !== newDeps[i])
+  }
+}
+
+function memo<T>(
+  key: string,
+  fn: () => T,
+  deps: undefined | $IntentionalAny[],
+): T {
+  const scope = hookScopeStack.peek()
+  if (!scope) {
+    throw new Error(`prism.memo() is called outside of a prism() call.`)
+  }
+
+  let memos = memosWeakMap.get(scope)
+
+  if (!memos) {
+    memos = {}
+    memosWeakMap.set(scope, memos)
+  }
+
+  if (!memos[key]) {
+    memos[key] = {
+      cachedValue: null,
+      deps: [{}],
+    }
+  }
+
+  const memo = memos[key]
+  if (depsHaveChanged(memo.deps, deps)) {
+    startIgnoringDependencies()
+
+    memo.cachedValue = safelyRun(fn, undefined).returnValue
+    stopIgnoringDependencies()
+    memo.deps = deps
+  }
+
+  return memo.cachedValue as $IntentionalAny as T
+}
+
+function state<T>(key: string, initialValue: T): [T, (val: T) => void] {
+  const {b, setValue} = prism.memo(
+    'state/' + key,
+    () => {
+      const b = new Box<T>(initialValue)
+      const setValue = (val: T) => b.set(val)
+      return {b, setValue}
+    },
+    [],
+  )
+
+  return [b.derivation.getValue(), setValue]
+}
+
+function ensurePrism(): void {
+  const scope = hookScopeStack.peek()
+  if (!scope) {
+    throw new Error(`The parent function is called outside of a prism() call.`)
+  }
+}
+
+function scope<T>(key: string, fn: () => T): T {
+  const parentScope = hookScopeStack.peek()
+  if (!parentScope) {
+    throw new Error(`prism.memo() is called outside of a prism() call.`)
+  }
+  const subScope = parentScope.sub(key)
+  hookScopeStack.push(subScope)
+  const ret = safelyRun(fn, undefined).returnValue
+  hookScopeStack.pop()
+  return ret as $IntentionalAny as T
+}
+
+type IPrismFn = {
+  <T>(fn: () => T): IDerivation<T>
+  ref: typeof ref
+  effect: typeof effect
+  memo: typeof memo
+  ensurePrism: typeof ensurePrism
+  state: typeof state
+  scope: typeof scope
+}
+
+const prism: IPrismFn = (fn) => {
+  return new PrismDerivation(fn)
+}
+
+prism.ref = ref
+prism.effect = effect
+prism.memo = memo
+prism.ensurePrism = ensurePrism
+prism.state = state
+prism.scope = scope
+
+export default prism

packages/dataverse2/src/index.ts

@@ -0,0 +1,14 @@
+export {default as Atom, isPointer, val, valueDerivation} from './Atom'
+export {default as Box} from './Box'
+export type {IBox} from './Box'
+export {default as AbstractDerivation} from './derivations/AbstractDerivation'
+export {default as ConstantDerivation} from './derivations/ConstantDerivation'
+export {default as DerivationFromSource} from './derivations/DerivationFromSource'
+export {isDerivation} from './derivations/IDerivation'
+export type {IDerivation} from './derivations/IDerivation'
+export {default as iterateAndCountTicks} from './derivations/iterateAndCountTicks'
+export {default as iterateOver} from './derivations/iterateOver'
+export {default as prism} from './derivations/prism/prism'
+export {default as pointer, getPointerParts} from './pointer'
+export type {Pointer} from './pointer'
+export {default as Ticker} from './Ticker'

packages/dataverse2/src/integration.test.ts

@@ -0,0 +1,32 @@
+import Atom, {val} from './Atom'
+import prism from './derivations/prism/prism'
+import Ticker from './Ticker'
+
+describe.skip(`dataverse2 integration tests`, () => {
+  describe(`identity pointers`, () => {
+    it(`should work`, () => {
+      const data = {foo: 'hi', bar: 0}
+      const a = new Atom(data)
+      const dataP = a.pointer
+      const bar = dataP.bar
+      expect(val(bar)).toEqual(0)
+
+      const d = prism(() => {
+        return val(bar)
+      })
+      expect(d.getValue()).toEqual(0)
+      const ticker = new Ticker()
+      const changes: number[] = []
+      d.changes().tap((c) => {
+        changes.push(c)
+      })
+      a.setState({...data, bar: 1})
+      ticker.tick()
+      expect(changes).toHaveLength(1)
+      expect(changes[0]).toEqual(1)
+      a.setState({...data, bar: 1})
+      ticker.tick()
+      expect(changes).toHaveLength(1)
+    })
+  })
+})

packages/dataverse2/src/pointer.ts

@@ -0,0 +1,98 @@
+import type {$IntentionalAny} from './types'
+
+type PathToProp = Array<string | number>
+
+type PointerMeta = {
+  root: {}
+  path: (string | number)[]
+}
+
+export type UnindexableTypesForPointer =
+  | number
+  | string
+  | boolean
+  | null
+  | void
+  | undefined
+  | Function // eslint-disable-line @typescript-eslint/ban-types
+
+export type UnindexablePointer = {
+  [K in $IntentionalAny]: Pointer<undefined>
+}
+
+const pointerMetaWeakMap = new WeakMap<{}, PointerMeta>()
+
+export type PointerType<O> = {
+  $$__pointer_type: O
+}
+
+export type Pointer<O> = PointerType<O> &
+  (O extends UnindexableTypesForPointer
+    ? UnindexablePointer
+    : unknown extends O
+    ? UnindexablePointer
+    : O extends (infer T)[]
+    ? Pointer<T>[]
+    : O extends {}
+    ? {[K in keyof O]-?: Pointer<O[K]>}
+    : UnindexablePointer)
+
+const pointerMetaSymbol = Symbol('pointerMeta')
+
+const cachedSubPointersWeakMap = new WeakMap<
+  {},
+  Record<string | number, Pointer<unknown>>
+>()
+
+const handler = {
+  get(obj: {}, prop: string | typeof pointerMetaSymbol): $IntentionalAny {
+    if (prop === pointerMetaSymbol) return pointerMetaWeakMap.get(obj)!
+
+    let subs = cachedSubPointersWeakMap.get(obj)
+    if (!subs) {
+      subs = {}
+      cachedSubPointersWeakMap.set(obj, subs)
+    }
+
+    if (subs[prop]) return subs[prop]
+
+    const meta = pointerMetaWeakMap.get(obj)!
+
+    const subPointer = pointer({root: meta.root, path: [...meta.path, prop]})
+    subs[prop] = subPointer
+    return subPointer
+  },
+}
+
+export const getPointerMeta = (p: Pointer<$IntentionalAny>): PointerMeta => {
+  const meta: PointerMeta = p[
+    pointerMetaSymbol as unknown as $IntentionalAny
+  ] as $IntentionalAny
+  return meta
+}
+
+export const getPointerParts = (
+  p: Pointer<$IntentionalAny>,
+): {root: {}; path: PathToProp} => {
+  const {root, path} = getPointerMeta(p)
+  return {root, path}
+}
+
+function pointer<O>({
+  root,
+  path,
+}: {
+  root: {}
+  path: Array<string | number>
+}): Pointer<O>
+function pointer(args: {root: {}; path?: Array<string | number>}) {
+  const meta: PointerMeta = {
+    root: args.root as $IntentionalAny,
+    path: args.path ?? [],
+  }
+  const hiddenObj = {}
+  pointerMetaWeakMap.set(hiddenObj, meta)
+  return new Proxy(hiddenObj, handler) as Pointer<$IntentionalAny>
+}
+
+export default pointer

packages/dataverse2/src/setupTestEnv.ts

@@ -0,0 +1 @@
+export {}

packages/dataverse2/src/types.ts

@@ -0,0 +1,6 @@
+/** For `any`s that aren't meant to stay `any`*/
+export type $FixMe = any
+/** For `any`s that we don't care about */
+export type $IntentionalAny = any
+
+export type VoidFn = () => void

packages/dataverse2/src/utils/Emitter.test.ts

@@ -0,0 +1,19 @@
+import Emitter from './Emitter'
+
+describe.skip('DataVerse2.Emitter', () => {
+  it('should work', () => {
+    const e: Emitter<string> = new Emitter()
+    e.emit('no one will see this')
+    e.emit('nor this')
+
+    const tappedEvents: string[] = []
+    const untap = e.tappable.tap((payload) => {
+      tappedEvents.push(payload)
+    })
+    e.emit('foo')
+    e.emit('bar')
+    untap()
+    e.emit('baz')
+    expect(tappedEvents).toMatchObject(['foo', 'bar'])
+  })
+})

packages/dataverse2/src/utils/Emitter.ts

@@ -0,0 +1,55 @@
+import Tappable from './Tappable'
+
+type Tapper<V> = (v: V) => void
+type Untap = () => void
+
+export default class Emitter<V> {
+  private _tappers: Map<any, (v: V) => void>
+  private _lastTapperId: number
+  readonly tappable: Tappable<V>
+  private _onNumberOfTappersChangeListener: undefined | ((n: number) => void)
+
+  constructor() {
+    this._lastTapperId = 0
+    this._tappers = new Map()
+    this.tappable = new Tappable({
+      tapToSource: (cb: Tapper<V>) => {
+        return this._tap(cb)
+      },
+    })
+  }
+
+  _tap(cb: Tapper<V>): Untap {
+    const tapperId = this._lastTapperId++
+    this._tappers.set(tapperId, cb)
+    this._onNumberOfTappersChangeListener &&
+      this._onNumberOfTappersChangeListener(this._tappers.size)
+    return () => {
+      this._removeTapperById(tapperId)
+    }
+  }
+
+  _removeTapperById(id: number) {
+    const oldSize = this._tappers.size
+    this._tappers.delete(id)
+    const newSize = this._tappers.size
+    if (oldSize !== newSize) {
+      this._onNumberOfTappersChangeListener &&
+        this._onNumberOfTappersChangeListener(this._tappers.size)
+    }
+  }
+
+  emit(payload: V) {
+    this._tappers.forEach((cb) => {
+      cb(payload)
+    })
+  }
+
+  hasTappers() {
+    return this._tappers.size !== 0
+  }
+
+  onNumberOfTappersChange(cb: (n: number) => void) {
+    this._onNumberOfTappersChangeListener = cb
+  }
+}

packages/dataverse2/src/utils/EventEmitter.ts

@@ -0,0 +1,56 @@
+import forEach from 'lodash-es/forEach'
+import without from 'lodash-es/without'
+import type {$FixMe} from '../types'
+
+type Listener = (v: $FixMe) => void
+
+/**
+ * A simple barebones event emitter
+ */
+export default class EventEmitter {
+  _listenersByType: {[eventName: string]: Array<Listener>}
+  constructor() {
+    this._listenersByType = {}
+  }
+
+  addEventListener(eventName: string, listener: Listener) {
+    const listeners =
+      this._listenersByType[eventName] ||
+      (this._listenersByType[eventName] = [])
+
+    listeners.push(listener)
+
+    return this
+  }
+
+  removeEventListener(eventName: string, listener: Listener) {
+    const listeners = this._listenersByType[eventName]
+    if (listeners) {
+      const newListeners = without(listeners, listener)
+      if (newListeners.length === 0) {
+        delete this._listenersByType[eventName]
+      } else {
+        this._listenersByType[eventName] = newListeners
+      }
+    }
+
+    return this
+  }
+
+  emit(eventName: string, payload: unknown) {
+    const listeners = this.getListenersFor(eventName)
+    if (listeners) {
+      forEach(listeners, (listener) => {
+        listener(payload)
+      })
+    }
+  }
+
+  getListenersFor(eventName: string) {
+    return this._listenersByType[eventName]
+  }
+
+  hasListenersFor(eventName: string) {
+    return this.getListenersFor(eventName) ? true : false
+  }
+}

packages/dataverse2/src/utils/PathBasedReducer.ts

@@ -0,0 +1,133 @@
+export type PathBasedReducer<S, ReturnType> = {
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+    A5 extends keyof S[A0][A1][A2][A3][A4],
+    A6 extends keyof S[A0][A1][A2][A3][A4][A5],
+    A7 extends keyof S[A0][A1][A2][A3][A4][A5][A6],
+    A8 extends keyof S[A0][A1][A2][A3][A4][A5][A6][A7],
+    A9 extends keyof S[A0][A1][A2][A3][A4][A5][A6][A7][A8],
+    A10 extends keyof S[A0][A1][A2][A3][A4][A5][A6][A7][A8][A9],
+  >(
+    addr: [A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10],
+    reducer: (
+      d: S[A0][A1][A2][A3][A4][A5][A6][A7][A8][A9][A10],
+    ) => S[A0][A1][A2][A3][A4][A5][A6][A7][A8][A9][A10],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+    A5 extends keyof S[A0][A1][A2][A3][A4],
+    A6 extends keyof S[A0][A1][A2][A3][A4][A5],
+    A7 extends keyof S[A0][A1][A2][A3][A4][A5][A6],
+    A8 extends keyof S[A0][A1][A2][A3][A4][A5][A6][A7],
+    A9 extends keyof S[A0][A1][A2][A3][A4][A5][A6][A7][A8],
+  >(
+    addr: [A0, A1, A2, A3, A4, A5, A6, A7, A8, A9],
+    reducer: (
+      d: S[A0][A1][A2][A3][A4][A5][A6][A7][A8][A9],
+    ) => S[A0][A1][A2][A3][A4][A5][A6][A7][A8][A9],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+    A5 extends keyof S[A0][A1][A2][A3][A4],
+    A6 extends keyof S[A0][A1][A2][A3][A4][A5],
+    A7 extends keyof S[A0][A1][A2][A3][A4][A5][A6],
+    A8 extends keyof S[A0][A1][A2][A3][A4][A5][A6][A7],
+  >(
+    addr: [A0, A1, A2, A3, A4, A5, A6, A7, A8],
+    reducer: (
+      d: S[A0][A1][A2][A3][A4][A5][A6][A7][A8],
+    ) => S[A0][A1][A2][A3][A4][A5][A6][A7][A8],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+    A5 extends keyof S[A0][A1][A2][A3][A4],
+    A6 extends keyof S[A0][A1][A2][A3][A4][A5],
+    A7 extends keyof S[A0][A1][A2][A3][A4][A5][A6],
+  >(
+    addr: [A0, A1, A2, A3, A4, A5, A6, A7],
+    reducer: (
+      d: S[A0][A1][A2][A3][A4][A5][A6][A7],
+    ) => S[A0][A1][A2][A3][A4][A5][A6][A7],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+    A5 extends keyof S[A0][A1][A2][A3][A4],
+    A6 extends keyof S[A0][A1][A2][A3][A4][A5],
+  >(
+    addr: [A0, A1, A2, A3, A4, A5, A6],
+    reducer: (
+      d: S[A0][A1][A2][A3][A4][A5][A6],
+    ) => S[A0][A1][A2][A3][A4][A5][A6],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+    A5 extends keyof S[A0][A1][A2][A3][A4],
+  >(
+    addr: [A0, A1, A2, A3, A4, A5],
+    reducer: (d: S[A0][A1][A2][A3][A4][A5]) => S[A0][A1][A2][A3][A4][A5],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+    A4 extends keyof S[A0][A1][A2][A3],
+  >(
+    addr: [A0, A1, A2, A3, A4],
+    reducer: (d: S[A0][A1][A2][A3][A4]) => S[A0][A1][A2][A3][A4],
+  ): ReturnType
+
+  <
+    A0 extends keyof S,
+    A1 extends keyof S[A0],
+    A2 extends keyof S[A0][A1],
+    A3 extends keyof S[A0][A1][A2],
+  >(
+    addr: [A0, A1, A2, A3],
+    reducer: (d: S[A0][A1][A2][A3]) => S[A0][A1][A2][A3],
+  ): ReturnType
+
+  <A0 extends keyof S, A1 extends keyof S[A0], A2 extends keyof S[A0][A1]>(
+    addr: [A0, A1, A2],
+    reducer: (d: S[A0][A1][A2]) => S[A0][A1][A2],
+  ): ReturnType
+
+  <A0 extends keyof S, A1 extends keyof S[A0]>(
+    addr: [A0, A1],
+    reducer: (d: S[A0][A1]) => S[A0][A1],
+  ): ReturnType
+
+  <A0 extends keyof S>(addr: [A0], reducer: (d: S[A0]) => S[A0]): ReturnType
+
+  (addr: undefined[], reducer: (d: S) => S): ReturnType
+}

packages/dataverse2/src/utils/Stack.ts

@@ -0,0 +1,33 @@
+interface Node<Data> {
+  next: undefined | Node<Data>
+  data: Data
+}
+
+/**
+ * Just a simple LinkedList
+ */
+export default class Stack<Data> {
+  _head: undefined | Node<Data>
+
+  constructor() {
+    this._head = undefined
+  }
+
+  peek() {
+    return this._head && this._head.data
+  }
+
+  pop() {
+    const head = this._head
+    if (!head) {
+      return undefined
+    }
+    this._head = head.next
+    return head.data
+  }
+
+  push(data: Data) {
+    const node = {next: this._head, data}
+    this._head = node
+  }
+}

packages/dataverse2/src/utils/Tappable.ts

@@ -0,0 +1,91 @@
+type Untap = () => void
+type UntapFromSource = () => void
+
+interface IProps<V> {
+  tapToSource: (cb: (payload: V) => void) => UntapFromSource
+}
+
+type Listener<V> = ((v: V) => void) | (() => void)
+
+export default class Tappable<V> {
+  private _props: IProps<V>
+  private _tappers: Map<number, {bivarianceHack(v: V): void}['bivarianceHack']>
+  private _untapFromSource: null | UntapFromSource
+  private _lastTapperId: number
+  private _untapFromSourceTimeout: null | NodeJS.Timer = null
+
+  constructor(props: IProps<V>) {
+    this._lastTapperId = 0
+    this._untapFromSource = null
+    this._props = props
+    this._tappers = new Map()
+  }
+
+  private _check() {
+    if (this._untapFromSource) {
+      if (this._tappers.size === 0) {
+        this._scheduleToUntapFromSource()
+        /*
+         * this._untapFromSource()
+         * this._untapFromSource = null
+         */
+      }
+    } else {
+      if (this._tappers.size !== 0) {
+        this._untapFromSource = this._props.tapToSource(this._cb)
+      }
+    }
+  }
+
+  private _scheduleToUntapFromSource() {
+    if (this._untapFromSourceTimeout !== null) return
+    this._untapFromSourceTimeout = setTimeout(() => {
+      this._untapFromSourceTimeout = null
+      if (this._tappers.size === 0) {
+        this._untapFromSource!()
+
+        this._untapFromSource = null
+      }
+    }, 0)
+  }
+
+  private _cb: any = (arg: any): void => {
+    this._tappers.forEach((cb) => {
+      cb(arg)
+    })
+  }
+
+  tap(cb: Listener<V>): Untap {
+    const tapperId = this._lastTapperId++
+    this._tappers.set(tapperId, cb)
+    this._check()
+    return () => {
+      this._removeTapperById(tapperId)
+    }
+  }
+
+  /*
+   * tapImmediate(cb: Listener<V>): Untap {
+   *   const ret = this.tap(cb)
+   *   return ret
+   * }
+   */
+
+  private _removeTapperById(id: number) {
+    this._tappers.delete(id)
+    this._check()
+  }
+
+  // /**
+  //  * @deprecated
+  //  */
+  // map<T>(transform: {bivarianceHack(v: V): T}['bivarianceHack']): Tappable<T> {
+  //   return new Tappable({
+  //     tapToSource: (cb: (v: T) => void) => {
+  //       return this.tap((v: $IntentionalAny) => {
+  //         return cb(transform(v))
+  //       })
+  //     },
+  //   })
+  // }
+}

packages/dataverse2/src/utils/typeTestUtils.ts

@@ -0,0 +1,12 @@
+import type {$IntentionalAny} from '../types'
+
+/**
+ * Useful in type tests, such as: const a: SomeType = _any
+ */
+export const _any: $IntentionalAny = null
+
+/**
+ * Useful in typeTests. If you want to ensure that value v follows type V,
+ * just write `expectType<V>(v)`
+ */
+export const expectType = <T extends unknown>(v: T): T => v

packages/dataverse2/src/utils/updateDeep.ts

@@ -0,0 +1,42 @@
+import type {$FixMe, $IntentionalAny} from '../types'
+
+export default function updateDeep<S>(
+  state: S,
+  path: (string | number | undefined)[],
+  reducer: (...args: $IntentionalAny[]) => $IntentionalAny,
+): S {
+  if (path.length === 0) return reducer(state)
+  return hoop(state, path as $IntentionalAny, reducer)
+}
+
+const hoop = (
+  s: $FixMe,
+  path: (string | number)[],
+  reducer: $FixMe,
+): $FixMe => {
+  if (path.length === 0) {
+    return reducer(s)
+  }
+  if (Array.isArray(s)) {
+    let [index, ...restOfPath] = path
+    index = parseInt(String(index), 10)
+    if (isNaN(index)) index = 0
+    const oldVal = s[index]
+    const newVal = hoop(oldVal, restOfPath, reducer)
+    if (oldVal === newVal) return s
+    const newS = [...s]
+    newS.splice(index, 1, newVal)
+    return newS
+  } else if (typeof s === 'object' && s !== null) {
+    const [key, ...restOfPath] = path
+    const oldVal = s[key]
+    const newVal = hoop(oldVal, restOfPath, reducer)
+    if (oldVal === newVal) return s
+    const newS = {...s, [key]: newVal}
+    return newS
+  } else {
+    const [key, ...restOfPath] = path
+
+    return {[key]: hoop(undefined, restOfPath, reducer)}
+  }
+}