source release 1.0.0

.eslintrc.json

@@ -0,0 +1,25 @@
+{
+  "extends": [
+    "standard",
+    "eslint:recommended",
+    "plugin:@typescript-eslint/recommended",
+    "plugin:@typescript-eslint/recommended-requiring-type-checking"
+  ],
+  "parser": "@typescript-eslint/parser",
+  "parserOptions": {
+    "sourceType": "module",
+    "project": "./tsconfig.json",
+    "tsconfigRootDir": "."
+  },
+  "plugins": [
+    "@typescript-eslint"
+  ],
+  "overrides": [
+    {
+      "files": ["*.mts"],
+      "rules": {
+        "max-len": ["error", 80]
+      }
+    }
+  ]
+}

.github/workflows/node.js.yml

@@ -0,0 +1,21 @@
+name: Node.js CI
+on: [push]
+jobs:
+  build:
+    runs-on: ubuntu-20.04
+
+    strategy:
+      matrix:
+        node-version: ["16.17.0"]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use Node.js ${{ matrix.node-version }}
+        uses: actions/setup-node@v2
+        with:
+          node-version: ${{ matrix.node-version }}
+          cache: "npm"
+      - run: npm ci
+      - run: npm run lint
+      - run: npm test
+      - run: npm run build

.gitignore

@@ -0,0 +1,5 @@
+node_modules/
+dist/
+.vscode/
+.nyc_output/
+*.tgz

.mocharc.json

@@ -0,0 +1,4 @@
+{
+  "extension": ["mts"],
+  "loader": "ts-node/esm"
+}

.nvmrc

@@ -0,0 +1 @@
+16.17.0

AUTHORS

@@ -0,0 +1,5 @@
+# This is the list of the significant contributors
+
+Max DeLiso
+Alex Matson
+Shishir Biyyala

CODE_OF_CONDUCT.md

@@ -0,0 +1,106 @@
+# Contributor Covenant Code of Conduct
+
+## Our Pledge
+
+We as members, contributors, and leaders pledge to make participation in our
+community a harassment-free experience for everyone, regardless of age, body
+size, visible or invisible disability, ethnicity, sex characteristics, gender
+identity and expression, level of experience, education, socio-economic status,
+nationality, personal appearance, race, caste, color, religion, or sexual
+identity and orientation.
+We pledge to act and interact in ways that contribute to an open, welcoming,
+diverse, inclusive, and healthy community.
+
+## Our Standards
+
+Examples of behavior that contributes to a positive environment for our
+community include:
+
+* Demonstrating empathy and kindness toward other people
+* Being respectful of differing opinions, viewpoints, and experiences
+* Giving and gracefully accepting constructive feedback
+* Accepting responsibility and apologizing to those affected by our mistakes,
+and learning from the experience
+* Focusing on what is best not just for us as individuals, but for the overall
+community
+
+Examples of unacceptable behavior include:
+
+* The use of sexualized language or imagery, and sexual attention or advances of
+any kind
+* Trolling, insulting or derogatory comments, and personal or political attacks
+* Public or private harassment
+* Publishing others’ private information, such as a physical or email address,
+without their explicit permission
+* Other conduct which could reasonably be considered inappropriate in a
+professional setting
+
+## Enforcement Responsibilities
+
+Community leaders are responsible for clarifying and enforcing our standards of
+acceptable behavior and will take appropriate and fair corrective action in
+response to any behavior that they deem inappropriate, threatening, offensive,
+or harmful.
+Community leaders have the right and responsibility to remove, edit, or reject
+comments, commits, code, wiki edits, issues, and other contributions that are
+not aligned to this Code of Conduct, and will communicate reasons for moderation
+decisions when appropriate.
+Scope
+This Code of Conduct applies within all community spaces, and also applies when
+an individual is officially representing the community in public spaces.
+Examples of representing our community include using an official e-mail address,
+posting via an official social media account, or acting as an appointed
+representative at an online or offline event.
+Enforcement
+Instances of abusive, harassing, or otherwise unacceptable behavior may be
+reported to the community leaders responsible for enforcement by e-mailing
+me@maxdeliso.name with the subject "COC violation."
+All complaints will be reviewed and investigated promptly and fairly.
+All community leaders are obligated to respect the privacy and security of the
+reporter of any incident.
+
+## Enforcement Guidelines
+
+Community leaders will follow these Community Impact Guidelines in determining
+the consequences for any action they deem in violation of this Code of Conduct:
+
+1. Correction
+Community Impact: Use of inappropriate language or other behavior deemed
+unprofessional or unwelcome in the community.
+Consequence: A private, written warning from community leaders, providing
+clarity around the nature of the violation and an explanation of why the
+behavior was inappropriate. A public apology may be requested.
+2. Warning
+Community Impact: A violation through a single incident or series of
+actions.
+Consequence: A warning with consequences for continued behavior. No
+interaction with the people involved, including unsolicited interaction with
+those enforcing the Code of Conduct, for a specified period of time. This
+includes avoiding interactions in community spaces as well as external channels
+like social media. Violating these terms may lead to a temporary or permanent
+ban.
+3. Temporary Ban
+Community Impact: A serious violation of community standards, including
+sustained inappropriate behavior.
+Consequence: A temporary ban from any sort of interaction or public
+communication with the community for a specified period of time. No public or
+private interaction with the people involved, including unsolicited interaction
+with those enforcing the Code of Conduct, is allowed during this period.
+Violating these terms may lead to a permanent ban.
+4. Permanent Ban
+Community Impact: Demonstrating a pattern of violation of community
+standards, including sustained inappropriate behavior, harassment of an
+individual, or aggression toward or disparagement of classes of individuals.
+Consequence: A permanent ban from any sort of public interaction within the
+community.
+
+## Attribution
+
+This Code of Conduct is adapted from the Contributor Covenant,
+version 2.1, available at
+<https://www.contributor-covenant.org/version/2/1/code_of_conduct.html>.
+Community Impact Guidelines were inspired by
+Mozilla’s code of conduct enforcement ladder.
+For answers to common questions about this code of conduct, see the FAQ at
+<https://www.contributor-covenant.org/faq>. Translations are available at
+<https://www.contributor-covenant.org/translations>.

LICENSE

@@ -0,0 +1,9 @@
+# The MIT License (MIT)
+
+Copyright © 2022 Joseph Maximilian DeLiso
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

@@ -0,0 +1,19 @@
+# SKI in TS
+
+An implementation of a parser, evaluator, printer, and serializer for the [SKI](https://en.wikipedia.org/wiki/SKI_combinator_calculus) combinators in [Typescript](https://www.typescriptlang.org/).
+
+## Books
+
+* [Combinators: A Centennial View, Stephen Wolfram](https://www.amazon.com/dp/1579550436/ref=nosim?tag=YOURASSOCIATEID)
+* [To Mock a Mockingbird, Raymond Smullyan](https://www.amazon.com/dp/0192801422/ref=nosim?tag=YOURASSOCIATEID)
+* [Combinatory Logic Volume I, Haskell Brooks Curry & Robert Feys](https://www.amazon.com/dp/B0041N5RDC/ref=nosim?tag=YOURASSOCIATEID)
+
+## Papers
+
+* Turner, David. “A new implementation technique for applicative languages.” Software: Practice and Experience 9 (1979): n. pag.
+* Stoye, William et al. “Some practical methods for rapid combinator reduction.” LFP '84 (1984).
+
+## Status
+
+[![Node.js CI](https://github.com/maxdeliso/typed-ski/actions/workflows/node.js.yml/badge.svg?branch=main)](https://github.com/maxdeliso/typed-ski/actions/workflows/node.js.yml)
+[![COC](https://img.shields.io/badge/Contributor%20Covenant-2.1-4baaaa.svg)](CODE_OF_CONDUCT.md)

lib/evaluator.mts

@@ -0,0 +1,168 @@
+import { Expression } from './expression.mjs'
+import { nt } from './nonterminal.mjs'
+import { TerminalSymbol } from './terminal.mjs'
+
+/**
+  * the shape of an evaluation result.
+  * altered is set if the evaluation step changed the input.
+  * expr is the evaluation output.
+  */
+export interface Result<E> {
+  altered: boolean;
+  expr: E;
+}
+
+/**
+ * a computation step; takes an expression and returns a result.
+ */
+export type Step<E> = (expr: E) => Result<E>
+
+/**
+ * the SKI combinator single step reduction function.
+ * @param expr the input expression.
+ * @returns the evaluation result.
+ */
+export const stepOnce: Step<Expression> =
+  (expr: Expression) => scanStep(expr, [stepOnceI, stepOnceK, stepOnceS])
+
+const stepOnceI: Step<Expression> =
+  (expr: Expression) => treeStep(expr, stepI)
+
+const stepOnceK: Step<Expression> =
+  (expr: Expression) => treeStep(expr, stepK)
+
+const stepOnceS: Step<Expression> =
+  (expr: Expression) => treeStep(expr, stepS)
+
+/**
+ * @param expr the expression to scan with steppers.
+ * @param steppers a list of steppers to try on the entire expression.
+ * @returns the expression with the first possible step in the list applied.
+ *
+ * NOTE: this is an eagerly returning fold
+ */
+const scanStep = (expr: Expression, steppers: Array<Step<Expression>>):
+  Result<Expression> => {
+  for (const step of steppers) {
+    const result = step(expr)
+
+    if (result.altered) {
+      return result
+    }
+  }
+
+  return {
+    altered: false,
+    expr
+  }
+}
+
+/**
+ * @param expr the input expression
+ * @param step a stepper
+ * @returns the result of traversing the tree to determine if the step
+ * resulted in an altering.
+ *
+ * NOTE: this is an implementation of DFS where the expression
+ * is the input and a singular function that processes an expression
+ * and returns either nothing or some result, returning eagerly.
+ */
+function treeStep (expr: Expression, step: Step<Expression>):
+  Result<Expression> {
+  switch (expr.kind) {
+    case 'terminal':
+      return ({
+        altered: false,
+        expr
+      })
+
+    case 'non-terminal': {
+      const currentResult = step(expr)
+
+      if (currentResult.altered) {
+        return currentResult
+      }
+
+      const lftStepResult = treeStep(expr.lft, step)
+
+      if (lftStepResult.altered) {
+        return ({
+          altered: true,
+          expr: nt(lftStepResult.expr, expr.rgt)
+        })
+      }
+
+      const rgtStepResult = treeStep(expr.rgt, step)
+
+      return {
+        altered: rgtStepResult.altered,
+        expr: nt(expr.lft, rgtStepResult.expr)
+      }
+    }
+  }
+}
+
+type ExtractStep<E> = (expr: E) => E | false
+
+function extractStep (expr: Expression, extractStep: ExtractStep<Expression>):
+  Result<Expression> {
+  const extractionResult = extractStep(expr)
+
+  if (extractionResult) {
+    return ({ altered: true, expr: extractionResult })
+  } else {
+    return ({ altered: false, expr })
+  }
+}
+
+/*
+ * identity
+ * Ix = x
+ */
+const stepI: Step<Expression> = (expr: Expression) =>
+  extractStep(
+    expr, (expr: Expression) =>
+      expr.kind === 'non-terminal' &&
+      expr.lft.kind === 'terminal' &&
+      expr.lft.sym === TerminalSymbol.I &&
+      expr.rgt
+  )
+
+/*
+ * constant
+ * Kxy = x
+ */
+const stepK: Step<Expression> = (expr: Expression) =>
+  extractStep(
+    expr, (expr: Expression) =>
+      expr.kind === 'non-terminal' &&
+      expr.lft.kind === 'non-terminal' &&
+      expr.lft.lft.kind === 'terminal' &&
+      expr.lft.lft.sym === TerminalSymbol.K &&
+      expr.lft.rgt
+  )
+
+/*
+ * fusion
+ * Sxyz = xz(yz)
+ */
+const stepS: Step<Expression> = (expr: Expression) =>
+  extractStep(
+    expr, (expr: Expression) => {
+      if (
+        expr.kind === 'non-terminal' &&
+        expr.lft.kind === 'non-terminal' &&
+        expr.lft.lft.kind === 'non-terminal' &&
+        expr.lft.lft.lft.kind === 'terminal' &&
+        expr.lft.lft.lft.sym === TerminalSymbol.S
+      ) {
+        const x = expr.lft.lft.rgt
+        const y = expr.lft.rgt
+        const z = expr.rgt
+
+        return nt(nt(x, z), nt(y, z))
+      } else {
+        return false
+      }
+    }
+  )