es6/step2_eval.mjs

   1 import rl from './node_readline.js'
   2 const readline = rl.readline
   3 import { _list_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 (typeof ast === 'symbol') {
  13         if (ast in env) {
  14             return env[ast]
  15         } else {
  16             throw Error(`'${Symbol.keyFor(ast)}' not found`)
  17         }
  18     } else if (ast instanceof Array) {
  19         return ast.map(x => EVAL(x, env))
  20     } else if (ast instanceof Map) {
  21         let new_hm = new Map()
  22         ast.forEach((v, k) => new_hm.set(EVAL(k, env), EVAL(v, env)))
  23         return new_hm
  24     } else {
  25         return ast
  26     }
  27 }
  28
  29 const EVAL = (ast, env) => {
  30     if (!_list_Q(ast)) { return eval_ast(ast, env) }
  31     if (ast.length === 0) { return ast }
  32
  33     const [f, ...args] = eval_ast(ast, env)
  34     return f(...args)
  35 }
  36
  37 // print
  38 const PRINT = exp => pr_str(exp, true)
  39
  40 // repl
  41 var repl_env = {[Symbol.for('+')]: (a,b) => a+b,
  42                 [Symbol.for('-')]: (a,b) => a-b,
  43                 [Symbol.for('*')]: (a,b) => a*b,
  44                 [Symbol.for('/')]: (a,b) => a/b}
  45 const REP = str => PRINT(EVAL(READ(str), repl_env))
  46
  47 while (true) {
  48     let line = readline('user> ')
  49     if (line == null) break
  50     try {
  51         if (line) { console.log(REP(line)) }
  52     } catch (exc) {
  53         if (exc instanceof BlankException) { continue }
  54         if (exc instanceof Error) { console.warn(exc.stack) }
  55         else { console.warn(`Error: ${exc}`) }
  56     }
  57 }