impls/ts/step2_eval.ts

   1 import { readline } from "./node_readline";
   2
   3 import { Node, MalType, MalNumber, MalList, MalVector, MalHashMap, MalFunction, isSeq } from "./types";
   4 import { readStr } from "./reader";
   5 import { prStr } from "./printer";
   6
   7 // READ
   8 function read(str: string): MalType {
   9     return readStr(str);
  10 }
  11
  12 interface MalEnvironment {
  13     [key: string]: MalFunction;
  14 }
  15
  16 function evalAST(ast: MalType, env: MalEnvironment): MalType {
  17     switch (ast.type) {
  18         case Node.Symbol:
  19             const f = env[ast.v];
  20             if (!f) {
  21                 throw new Error(`unknown symbol: ${ast.v}`);
  22             }
  23             return f;
  24         case Node.List:
  25             return new MalList(ast.list.map(ast => evalMal(ast, env)));
  26         case Node.Vector:
  27             return new MalVector(ast.list.map(ast => evalMal(ast, env)));
  28         case Node.HashMap:
  29             const list: MalType[] = [];
  30             for (const [key, value] of ast.entries()) {
  31                 list.push(key);
  32                 list.push(evalMal(value, env));
  33             }
  34             return new MalHashMap(list);
  35         default:
  36             return ast;
  37     }
  38 }
  39
  40 // EVAL
  41 function evalMal(ast: MalType, env: MalEnvironment): MalType {
  42     if (ast.type !== Node.List) {
  43         return evalAST(ast, env);
  44     }
  45     if (ast.list.length === 0) {
  46         return ast;
  47     }
  48     const result = evalAST(ast, env);
  49     if (!isSeq(result)) {
  50         throw new Error(`unexpected return type: ${result.type}, expected: list or vector`);
  51     }
  52     const [f, ...args] = result.list;
  53     if (f.type !== Node.Function) {
  54         throw new Error(`unexpected token: ${f.type}, expected: function`);
  55     }
  56     return f.func(...args);
  57 }
  58
  59 // PRINT
  60 function print(exp: MalType): string {
  61     return prStr(exp);
  62 }
  63
  64 const replEnv: MalEnvironment = {
  65     "+": MalFunction.fromBootstrap((a?: MalNumber, b?: MalNumber) => new MalNumber(a!.v + b!.v)),
  66     "-": MalFunction.fromBootstrap((a?: MalNumber, b?: MalNumber) => new MalNumber(a!.v - b!.v)),
  67     "*": MalFunction.fromBootstrap((a?: MalNumber, b?: MalNumber) => new MalNumber(a!.v * b!.v)),
  68     "/": MalFunction.fromBootstrap((a?: MalNumber, b?: MalNumber) => new MalNumber(a!.v / b!.v)),
  69 };
  70 function rep(str: string): string {
  71     return print(evalMal(read(str), replEnv));
  72 }
  73
  74 while (true) {
  75     const line = readline("user> ");
  76     if (line == null) {
  77         break;
  78     }
  79     if (line === "") {
  80         continue;
  81     }
  82     try {
  83         console.log(rep(line));
  84     } catch (e) {
  85         const err: Error = e;
  86         console.error(err.message);
  87     }
  88 }