ts/step2_eval.ts

   1 import { readline } from "./node_readline";
   2
   3 import { MalType, MalNumber, MalList, MalVector, MalHashMap, MalFunction } from "./types";
   4 import { readStr } from "./reader";
   5 import { prStr } from "./printer";
   6
   7 function read(str: string): MalType {
   8     return readStr(str);
   9 }
  10
  11 interface MalEnvironment {
  12     [key: string]: MalFunction;
  13 }
  14
  15 function evalAST(ast: MalType, env: MalEnvironment): MalType {
  16     switch (ast.type) {
  17         case "symbol":
  18             const f = env[ast.v];
  19             if (!f) {
  20                 throw new Error(`unknown symbol: ${ast.v}`);
  21             }
  22             return f;
  23         case "list":
  24             return new MalList(ast.list.map(ast => evalSexp(ast, env)));
  25         case "vector":
  26             return new MalVector(ast.list.map(ast => evalSexp(ast, env)));
  27         case "hash-map":
  28             const list: MalType[] = [];
  29             for (const [key, value] of ast.map) {
  30                 list.push(key);
  31                 list.push(evalSexp(value, env));
  32             }
  33             return new MalHashMap(list);
  34         default:
  35             return ast;
  36     }
  37 }
  38
  39 function evalSexp(ast: MalType, env: MalEnvironment): MalType {
  40     if (ast.type !== "list") {
  41         return evalAST(ast, env);
  42     }
  43     if (ast.list.length === 0) {
  44         return ast;
  45     }
  46     const result = evalAST(ast, env) as MalList;
  47     const [f, ...rest] = result.list;
  48     if (!MalFunction.is(f)) {
  49         throw new Error(`unexpected token: ${f.type}, expected: function`);
  50     }
  51     return f.func(...rest);
  52 }
  53
  54 function print(exp: MalType): string {
  55     return prStr(exp);
  56 }
  57
  58 const replEnv: MalEnvironment = {
  59     "+": new MalFunction((a?: MalNumber, b?: MalNumber) => new MalNumber(a!.v + b!.v)),
  60     "-": new MalFunction((a?: MalNumber, b?: MalNumber) => new MalNumber(a!.v - b!.v)),
  61     "*": new MalFunction((a?: MalNumber, b?: MalNumber) => new MalNumber(a!.v * b!.v)),
  62     "/": new MalFunction((a?: MalNumber, b?: MalNumber) => new MalNumber(a!.v / b!.v)),
  63 };
  64 function rep(str: string): string {
  65     return print(evalSexp(read(str), replEnv));
  66 }
  67
  68 while (true) {
  69     const line = readline("user> ");
  70     if (line == null) {
  71         break;
  72     }
  73     if (line === "") {
  74         continue;
  75     }
  76     try {
  77         console.log(rep(line));
  78     } catch (e) {
  79         const err: Error = e;
  80         console.error(err.message);
  81     }
  82 }