implement most of the TS version

typescript/Eval.ts

@@ -1,5 +1,24 @@
-import { BinExpr, emitCont, Result } from './Parse.js';
+import { BinExpr, emitBack, emitCont, isCont, result, Result } from './Parse.js';
 
 export function evalBin(b: Result<BinExpr>): Result<number> {
-  return emitCont(0, b.rem); // TODO
+  if (isCont(b)) {
+    const br = result(b);
+
+    if (br.lhs.type === 'digit' && br.oper.type === 'oper' && br.rhs.type === 'digit') {
+      switch (br.oper.val) {
+        case '+':
+          return emitCont(br.lhs.val + br.rhs.val, b.rem);
+        case '-':
+          return emitCont(br.lhs.val - br.rhs.val, b.rem);
+        case '*':
+          return emitCont(br.lhs.val * br.rhs.val, b.rem);
+        case '/':
+          return emitCont(br.lhs.val / br.rhs.val, b.rem);
+        default:
+          return emitBack(b.rem);
+      }
+    }
+  }
+
+  return emitBack(b.rem);
 }

typescript/Maybe.ts

@@ -32,3 +32,11 @@ export function isJust<T>(m: Maybe<T>): m is Just<T> {
 export function isNothing<T>(m: Maybe<T>): m is Nothing {
   return Object.getOwnPropertyDescriptor(m, SymbolNothing) !== undefined;
 }
+
+export function mustExist<T>(m: T | undefined): T {
+  if (m === undefined) {
+    throw new Error('this is where things start to go wrong');
+  } else {
+    return m;
+  }
+}

typescript/Parse.ts

@@ -1,5 +1,5 @@
-import { isJust, isNothing, Just, just, Maybe, Nothing, nothing } from './Maybe.js';
-import { map, split } from './Util.js';
+import { isJust, isNothing, Just, just, Maybe, mustExist, Nothing, nothing, SymbolJust } from './Maybe.js';
+import { map, primStringToList, split } from './Util.js';
 
 export type Token = {
   type: 'digit';
@@ -17,6 +17,33 @@ export type Token = {
   type: 'term';
 };
 
+export function digit(val: number): Token {
+  return {
+    type: 'digit',
+    val,
+  };
+}
+
+export function oper(val: string): Token {
+  return {
+    type: 'oper',
+    val,
+  };
+}
+
+export function skip(val: string): Token {
+  return {
+    type: 'skip',
+    val,
+  };
+}
+
+export function term(): Token {
+  return {
+    type: 'term',
+  };
+}
+
 export interface BinExpr {
   oper: Token;
   lhs: Token;
@@ -25,21 +52,36 @@ export interface BinExpr {
 
 export interface Result<T, R = Maybe<T>> {
   res: R;
-  rem: Array<string>;
+  rem: ReadonlyArray<string>;
 }
 
-export function emitCont<T>(val: T, rem: Array<string>): Result<T> {
+export const DIGITS = primStringToList("0123456789");
+export const OPERS = primStringToList("-+*/");
+export const SKIPS = primStringToList(" ");
+
+export function emit<T>(val: Maybe<T>, rem: ReadonlyArray<string>): Result<T> {
+  return {
+    res: val,
+    rem,
+  };
+}
+
+export function emitBack<T>(rem: ReadonlyArray<string>): Result<T> {
+  return {
+    res: nothing(),
+    rem,
+  };
+}
+
+export function emitCont<T>(val: T, rem: ReadonlyArray<string>): Result<T> {
   return {
     res: just(val),
     rem,
   };
 }
 
-export function emitBack<T>(rem: Array<string>): Result<T> {
-  return {
-    res: nothing(),
-    rem,
-  };
+export function result<T>(r: Result<T, Just<T>>): T {
+  return r.res[SymbolJust];
 }
 
 export function isCont<T>(r: Result<T>): r is Result<T, Just<T>> {
@@ -50,34 +92,133 @@ export function isBack<T>(r: Result<T>): r is Result<T, Nothing> {
   return isNothing(r.res);
 }
 
-export function takeCons(cs: Array<string>, xs: Array<string>): Result<Array<string>> {
-  return emitBack([]); // TODO
+export function takeCons(cs: ReadonlyArray<string>, xs: ReadonlyArray<string>): Result<ReadonlyArray<string>> {
+  const acc: Array<string> = [];
+  const rem = Array.from(xs);
+
+  while (cs.includes(rem[0])) {
+    acc.push(mustExist(rem.shift()));
   }
 
-export function ignoreConst(cs: Array<string>, xs: Array<string>): Array<string> {
-  return xs; // TODO
+  return emitCont(acc, rem)
 }
 
-export function parseChar(): Result<Token> {
-  return emitBack([]); // TODO
+export function ignoreCons(cs: ReadonlyArray<string>, xs: ReadonlyArray<string>): ReadonlyArray<string> {
+  const rem = Array.from(xs);
+
+  while (cs.includes(rem[0])) {
+    rem.shift();
   }
 
-export function parseNat(): Result<number> {
-  return emitBack([]); // TODO
+  return rem;
 }
 
-export function takeNat(): Result<number> {
-  return emitBack([]); // TODO
+export function parseChar(c: string): Token {
+  switch (c) {
+    case '0':
+      return digit(0);
+    case '1':
+      return digit(1);
+    case '2':
+      return digit(2);
+    case '3':
+      return digit(3);
+    case '4':
+      return digit(4);
+    case '5':
+      return digit(5);
+    case '6':
+      return digit(6);
+    case '7':
+      return digit(7);
+    case '8':
+      return digit(8);
+    case '9':
+      return digit(9);
+    case '+':
+    case '-':
+    case '*':
+    case '/':
+      return oper(c);
+    case ' ':
+      return skip(c);
+    default:
+      return {
+        type: 'term',
+      };
+  }
 }
 
-export function parseOper() {}
-
-export function takeOper(): Result<Token> {
-  return emitBack([]); // TODO
+export function parseNat(a: Maybe<number>, cs: ReadonlyArray<string>): Result<number> {
+  if (cs.length === 0) {
+    return emit(a, []);
   }
 
-export function takeBin(): Result<BinExpr> {
-  return emitBack([]); // TODO
+  const [x, ...xs] = cs;
+  const t = parseChar(x);
+
+  if (t.type === 'digit') {
+    return emitCont(t.val, xs)
+  } else {
+    return emitBack(cs);
+  }
+}
+
+export function takeNat(s: ReadonlyArray<string>): Result<number> {
+  const cs = takeCons(DIGITS, s);
+
+  if (isCont(cs)) {
+    const n = parseNat(nothing(), result(cs));
+
+    if (isCont(n)) {
+      return emitCont(result(n), cs.rem);
+    }
+  }
+
+  return emitBack(cs.rem);
+}
+
+export function parseOper(s: ReadonlyArray<string>): Result<Token> {
+  if (s.length === 0) {
+    return emitBack([]);
+  }
+
+  const [x, ...xs] = s;
+  const o = parseChar(x);
+
+  if (o.type === 'oper') {
+    return emitCont(o, xs);
+  } else {
+    return emitBack(xs);
+  }
+}
+
+export function takeOper(s: ReadonlyArray<string>): Result<Token> {
+  return parseOper(s);
+}
+
+export function takeBin(s: ReadonlyArray<string>): Result<BinExpr> {
+  const lhs = takeNat(ignoreCons(SKIPS, s));
+
+  if (isCont(lhs)) {
+    const oper = takeOper(ignoreCons(SKIPS, lhs.rem));
+
+    if (isCont(oper)) {
+      const rhs = takeNat(ignoreCons(SKIPS, oper.rem));
+
+      if (isCont(rhs)) {
+        const bin: BinExpr = {
+          lhs: digit(result(lhs)),
+          rhs: digit(result(rhs)),
+          oper: result(oper),
+        };
+
+        return emitCont(bin, rhs.rem);
+      }
+    }
+  }
+
+  return emitBack(s);
 }
 
 export function takeLine(c: Array<string>): Array<Result<BinExpr>> {

typescript/Show.ts

@@ -5,14 +5,14 @@ export function show(n: number): string {
   return n.toString();
 }
 
-export function showList<T>(f: (t: T) => string, arr: Array<T>): string {
+export function showList<T>(f: (t: T) => string, arr: ReadonlyArray<T>): string {
   return arr.map(f).join(', ');
 }
 
 export function showResult<T>(f: (t: T) => string, r: Result<T>): string {
   if (isCont(r)) {
-    return f(r.res[SymbolJust]);
+    return 'result: ' + f(r.res[SymbolJust]);
   } else {
-    return r.rem.join('');
+    return 'remainder: ' + r.rem.join('');
   }
 }