es6/step2_eval.js

   1 import { readline } from './node_readline'
   2 import { _symbol, _symbol_Q, _list_Q, _vector, _vector_Q,
   3          _hash_map_Q } from './types'
   4 import { BlankException, read_str } from './reader'
   5 import { pr_str } from './printer'
   6
   7 // read
   8 const READ = (str) => read_str(str)
   9
  10 // eval
  11 const eval_ast = (ast, env) => {
  12     if (_symbol_Q(ast)) {
  13         if (ast in env) {
  14             return env[ast]
  15         } else {
  16             throw Error(`'${Symbol.keyFor(ast)}' not found`)
  17         }
  18     } else if (_list_Q(ast)) {
  19         return ast.map((x) => EVAL(x, env))
  20     } else if (_vector_Q(ast)) {
  21         return _vector(...ast.map((x) => EVAL(x, env)))
  22     } else if (_hash_map_Q(ast)) {
  23         let new_hm = new Map()
  24         for (let [k, v] of ast) {
  25             new_hm.set(EVAL(k, env), EVAL(v, env))
  26         }
  27         return new_hm
  28     } else {
  29         return ast
  30     }
  31 }
  32
  33 const EVAL = (ast, env) => {
  34     if (!_list_Q(ast)) { return eval_ast(ast, env) }
  35
  36     const [f, ...args] = eval_ast(ast, env)
  37     return f(...args)
  38 }
  39
  40 // print
  41 const PRINT = (exp) => pr_str(exp, true)
  42
  43 // repl
  44 var repl_env = {[_symbol('+')]: (a,b) => a+b,
  45                 [_symbol('-')]: (a,b) => a-b,
  46                 [_symbol('*')]: (a,b) => a*b,
  47                 [_symbol('/')]: (a,b) => a/b}
  48 const REP = (str) => PRINT(EVAL(READ(str), repl_env))
  49
  50 while (true) {
  51     let line = readline('user> ')
  52     if (line == null) break
  53     try {
  54         if (line) { console.log(REP(line)); }
  55     } catch (exc) {
  56         if (exc instanceof BlankException) { continue; }
  57         if (exc.stack) { console.log(exc.stack); }
  58         else           { console.log(`Error: ${exc}`); }
  59     }
  60 }