maxdeliso · maxdeliso · Jun 30, 2024 · Jun 30, 2024
diff --git a/.eslintrc.json b/.eslintrc.json
diff --git a/.github/workflows/node.js.yml b/.github/workflows/node.js.yml
@@ -15,7 +15,19 @@ jobs:
         with:
           node-version: ${{ matrix.node-version }}
           cache: "npm"
-      - run: npm ci
-      - run: npm run lint
-      - run: npm test
-      - run: npm run build
+      - name: Run yarn install
+        uses: borales/actions-yarn@v4
+        with:
+          cmd: install --frozen-lockfile
+      - name: Run lint
+        uses: borales/actions-yarn@v4
+        with:
+          cmd: run lint
+      - name: Run build
+        uses: borales/actions-yarn@v4
+        with:
+          cmd: build
+      - name: Run test
+        uses: borales/actions-yarn@v4
+        with:
+          cmd: test
diff --git a/README.md b/README.md
@@ -7,8 +7,9 @@ An implementation of a parser, evaluator, printer, and visualizer for the [SKI](
 In the checkout directory:
 
 ```bash
-npm run build
-npx ski
+yarn install
+yarn run build
+yarn run ski
 ```
 
 ## Books

diff --git a/bin/ski.ts b/bin/ski.ts
@@ -28,8 +28,8 @@ function colorizeExpression (expr: SKIExpression): string {
     case 'non-terminal': {
       return [
         '(',
-        `${colorizeExpression(expr.lft)}`,
-        `${colorizeExpression(expr.rgt)}`,
+        colorizeExpression(expr.lft),
+        colorizeExpression(expr.rgt),
         ')'
       ].join('')
     }
@@ -43,7 +43,7 @@ function formatted (expr: SKIExpression): string {
 function runTUI (): number {
   const term : Terminal = terminalKit.terminal
   const seed = hrtime.bigint()
-  const randomSeed = create(`${seed}`)
+  const randomSeed = create(seed.toString())
   const N = 32
   const MAX_ITER = 100
 
@@ -83,7 +83,7 @@ function runTUI (): number {
         }
 
         if (iterations === MAX_ITER) {
-          term.red(`stopped evaluating after ${iterations} iterations. \n`)
+          term.red(`stopped evaluating after ${iterations.toString()} iterations. \n`)
         }
 
         break

diff --git a/eslint.config.mjs b/eslint.config.mjs
@@ -0,0 +1,32 @@
+import eslint from '@eslint/js'
+import tseslint from 'typescript-eslint'
+import path from "path"
+import url from "url"
+
+const __meta_url = new url.URL(import.meta.url)
+const __filename = url.fileURLToPath(__meta_url)
+const __dirname = path.dirname(__filename)
+
+export default tseslint.config(
+  {
+    files: ["**/*.{ts,mjs}"],
+  },
+  {
+    ignores: [
+      "**/node_modules/**",
+      "build/**",
+    ],
+  },
+  eslint.configs.recommended,
+  ...tseslint.configs.strictTypeChecked,
+  ...tseslint.configs.stylisticTypeChecked,
+  ...tseslint.configs.recommendedTypeChecked,
+  {
+    languageOptions: {
+      parserOptions: {
+        project: true,
+        tsconfigRootDir: __dirname,
+      },
+    },
+  },
+);
diff --git a/lib/conversion/converter.ts b/lib/conversion/converter.ts
@@ -5,10 +5,9 @@ import { B, C } from '../consts/combinators'
 import { LambdaVar } from '../lambda/lambda'
 import { ConversionError } from './conversionError'
 
-type LambdaAbsMixed = {
+interface LambdaAbsMixed {
   kind: 'lambda-abs',
   name: string,
-  // eslint-disable-next-line no-use-before-define
   body: LambdaMixed
 }
 
@@ -143,7 +142,7 @@ const free = (needle: string, lm: LambdaMixed): boolean => {
   return idx !== undefined
 }
 
-const freeVariables = (lm: LambdaMixed): Array<string> => {
+const freeVariables = (lm: LambdaMixed): string[] => {
   switch (lm.kind) {
     case 'lambda-var':
       return [lm.name]

diff --git a/lib/evaluator/skiEvaluator.ts b/lib/evaluator/skiEvaluator.ts
@@ -95,7 +95,7 @@ const stepOnceS: SKIStep<SKIExpression> =
  */
 const scanStep = (
   expr: SKIExpression,
-  steppers: Array<SKIStep<SKIExpression>>
+  steppers: SKIStep<SKIExpression>[]
 ):
   SKIResult<SKIExpression> => {
   for (const step of steppers) {

diff --git a/lib/lambda/lambda.ts b/lib/lambda/lambda.ts
@@ -5,7 +5,7 @@ import { NonTerminal, nt } from '../nonterminal'
  *
  * For instance, in the expression "λx:a.y", this is just "y".
  */
-export type LambdaVar = {
+export interface LambdaVar {
   kind: 'lambda-var',
   name: string
 }
@@ -16,15 +16,13 @@ export const mkVar = (name: string): LambdaVar => ({
 })
 
 // λx.<body>, where x is a name
-type UntypedLambdaAbs = {
+interface UntypedLambdaAbs {
   kind: 'lambda-abs',
   name: string,
-  // eslint-disable-next-line no-use-before-define
   body: UntypedLambda
 }
 
 export const mkUntypedAbs =
-  // eslint-disable-next-line no-use-before-define
   (name: string, body: UntypedLambda): UntypedLambda => ({
     kind: 'lambda-abs',
     name,

diff --git a/lib/parser/appendable.ts b/lib/parser/appendable.ts
@@ -39,7 +39,7 @@ export class Appendable {
 
       if (top === undefined) {
         throw new Error('insertionSites should not have an undefined value')
-      } else if (top?.lft === undefined) {
+      } else if (top.lft === undefined) {
         top.lft = newNode
         this.insertionSites.push(top)
         return
@@ -50,9 +50,9 @@ export class Appendable {
     }
 
     let currentNode : SyntaxExpression = this.syn
-    const nodeStack : Array<SyntaxExpression> = []
+    const nodeStack : SyntaxExpression[] = []
 
-    while (currentNode !== undefined || nodeStack.length > 0) {
+    while (nodeStack.length > 0) {
       // traverse left, accumulating the spine on a stack
       while (currentNode !== undefined) {
         if (currentNode.kind === 'non-terminal') {

diff --git a/lib/parser/recursiveDescentBuffer.ts b/lib/parser/recursiveDescentBuffer.ts
@@ -12,7 +12,7 @@ export class RecursiveDescentBuffer {
   }
 
   peek (): string | null {
-    return this.buf[this.idx] || null
+    return this.buf[this.idx] ?? null
   }
 
   consume (): void {
@@ -29,14 +29,14 @@ export class RecursiveDescentBuffer {
 
   matchCh (ch: string): void {
     if (this.peek() !== ch) {
-      throw new ParseError(`Expected ${ch} but found ${this.peek() || 'null'}'`)
+      throw new ParseError(`Expected ${ch} but found ${this.peek() ?? 'null'}'`)
     }
 
     this.consume()
   }
 
   remaining (): boolean {
-    return this.buf[this.idx] !== undefined
+    return this.idx < this.buf.length
   }
 
   parseVariable (): string {

diff --git a/lib/parser/untyped.ts b/lib/parser/untyped.ts
@@ -38,12 +38,10 @@ function parseUntypedLambdaInternal (rdb: RecursiveDescentBuffer):
       nextTerm = mkVar(singleVar)
     }
 
-    if (nextTerm !== undefined) {
-      if (resultExpr === undefined) {
-        resultExpr = nextTerm
-      } else {
-        resultExpr = nt(resultExpr, nextTerm)
-      }
+    if (resultExpr === undefined) {
+      resultExpr = nextTerm
+    } else {
+      resultExpr = nt(resultExpr, nextTerm)
     }
   }
   if (resultExpr === undefined) {

diff --git a/lib/ski/church.ts b/lib/ski/church.ts
@@ -56,7 +56,6 @@ const toLambda = (exp: SKIExpression): any => {
         return (x: (_: any) => {(_: any): any; _: any }) =>
           (y: (_: any) => any) =>
             (z: any) =>
-            // eslint-disable-next-line @typescript-eslint/no-unsafe-return
               x(z)(y(z))
         // eslint-disable-next-line @typescript-eslint/no-unused-vars
       case SKITerminalSymbol.K: return (x: any) => (_y: any) => x

diff --git a/lib/ski/expression.ts b/lib/ski/expression.ts
@@ -34,8 +34,8 @@ export function prettyPrint (expr: SKIExpression): string {
     case 'non-terminal': {
       const printed = [
         '(',
-        `${prettyPrint(expr.lft)}`,
-        `${prettyPrint(expr.rgt)}`,
+        prettyPrint(expr.lft),
+        prettyPrint(expr.rgt),
         ')'
       ]
 

diff --git a/lib/ski/packer.ts b/lib/ski/packer.ts
@@ -2,7 +2,7 @@ import { SKIExpression } from './expression'
 import { nt } from '../nonterminal'
 import { term, SKITerminalSymbol } from './terminal'
 
-export type SymbolHeap = Array<SKITerminalSymbol | undefined>;
+export type SymbolHeap = (SKITerminalSymbol | undefined)[];
 
 export type BinaryHeap = Uint8Array
 
@@ -40,10 +40,8 @@ export function heapify (exp: SKIExpression): SymbolHeap {
 
       indexes.push(rgtIndex(idx))
       nodes.push(node.rgt)
-    } else if (node.kind === 'terminal') {
-      result[idx] = node.sym
     } else {
-      throw new Error('unexpected node kind')
+      result[idx] = node.sym
     }
   }
 
@@ -75,7 +73,7 @@ export function unheapify (heapSyms: SymbolHeap): SKIExpression {
 
 function unheapifyFrom (heapSyms: SymbolHeap, heapIdx: number): SKIExpression {
   if (heapIdx >= heapSyms.length) {
-    throw new Error(`heap index exceeded: ${heapIdx}. input is corrupt.`)
+    throw new Error(`heap index exceeded: ${heapIdx.toString()}. input is corrupt.`)
   }
 
   const heapValue = heapSyms[heapIdx]
@@ -108,10 +106,8 @@ function packSymbol (sym: SKITerminalSymbol | undefined): number {
     return 0b01
   } else if (sym === SKITerminalSymbol.K) {
     return 0b10
-  } else if (sym === SKITerminalSymbol.I) {
-    return 0b11
   } else {
-    throw new Error('Impossible.')
+    return 0b11
   }
 }
 
@@ -133,7 +129,7 @@ function unpackSymbol (n: number): SKITerminalSymbol | undefined {
   } else if (n === 0b11) {
     return SKITerminalSymbol.I
   } else {
-    throw new Error(`The number ${n} does not correspond to a symbol in SKI.`)
+    throw new Error(`The number ${n.toString()} does not correspond to a symbol in SKI.`)
   }
 }
 
@@ -182,20 +178,18 @@ export function packSymbolHeap (ts: SymbolHeap): BinaryHeap {
 export function unpackBinaryHeap (inputBytes: BinaryHeap): SymbolHeap {
   const result: SymbolHeap = []
 
-  for (let i = 0; i < inputBytes.length; i++) {
-    const byte = inputBytes[i] || 0
-
+  for (const by of inputBytes) {
     /*
      * 0 b 1100 0000 = 0 x C 0
      * 0 b 0011 0000 = 0 x 3 0
      * 0 b 0000 1100 = 0 x 0 C
      * 0 b 0000 0011 = 0 x 0 3
      */
     const fourSnakeEyes = [
-      (byte & 0xC0) >> 6,
-      (byte & 0x30) >> 4,
-      (byte & 0x0C) >> 2,
-      (byte & 0x03) >> 0
+      (by & 0xC0) >> 6,
+      (by & 0x30) >> 4,
+      (by & 0x0C) >> 2,
+      (by & 0x03) >> 0
     ]
 
     fourSnakeEyes

diff --git a/lib/typed/typedLambda.ts b/lib/typed/typedLambda.ts
@@ -22,11 +22,10 @@ import {
  * The type is a.
  * The body of the expression is y.
  */
-export type TypedLambdaAbs = {
+export interface TypedLambdaAbs {
   kind: 'typed-lambda-abstraction',
   varName: string,
   ty: Type,
-  // eslint-disable-next-line no-use-before-define
   body: TypedLambda
 }
 

diff --git a/lib/typed/types.ts b/lib/typed/types.ts
@@ -3,7 +3,7 @@ import { NonTerminal, nt } from '../nonterminal'
 import { Context, TypedLambda, mkTypedAbs, typecheck } from './typedLambda'
 import { TypeError } from './typeError'
 
-export type TypeVariable = {
+export interface TypeVariable {
   kind: 'type-var',
   typeName: string
 }