es6/step4_if_fn_do.js

   1 import { readline } from './node_readline'
   2 import { _list_Q } from './types'
   3 import { BlankException, read_str } from './reader'
   4 import { pr_str } from './printer'
   5 import { new_env, env_set, env_get } from './env'
   6 import { core_ns } from './core'
   7
   8 // read
   9 const READ = str => read_str(str)
  10
  11 // eval
  12 const eval_ast = (ast, env) => {
  13     if (typeof ast === 'symbol') {
  14         return env_get(env, ast)
  15     } else if (ast instanceof Array) {
  16         return ast.map(x => EVAL(x, env))
  17     } else if (ast instanceof Map) {
  18         let new_hm = new Map()
  19         ast.forEach((v, k) => new_hm.set(EVAL(k, env), EVAL(v, env)))
  20         return new_hm
  21     } else {
  22         return ast
  23     }
  24 }
  25
  26 const EVAL = (ast, env) => {
  27     //console.log('EVAL:', pr_str(ast, true))
  28     if (!_list_Q(ast)) { return eval_ast(ast, env) }
  29     if (ast.length === 0) { return ast }
  30
  31     const [a0, a1, a2, a3] = ast
  32     switch (typeof a0 === 'symbol' ? Symbol.keyFor(a0) : Symbol(':default')) {
  33         case 'def!':
  34             return env_set(env, a1, EVAL(a2, env))
  35         case 'let*':
  36             let let_env = new_env(env)
  37             for (let i=0; i < a1.length; i+=2) {
  38                 env_set(let_env, a1[i], EVAL(a1[i+1], let_env))
  39             }
  40             return EVAL(a2, let_env)
  41         case 'do':
  42             return eval_ast(ast.slice(1), env)[ast.length-2]
  43         case 'if':
  44             let cond = EVAL(a1, env)
  45             if (cond === null || cond === false) {
  46                 return typeof a3 !== 'undefined' ? EVAL(a3, env) : null
  47             } else {
  48                 return EVAL(a2, env)
  49             }
  50         case 'fn*':
  51             return (...args) => EVAL(a2, new_env(env, a1, args))
  52         default:
  53             let [f, ...args] = eval_ast(ast, env)
  54             return f(...args)
  55     }
  56 }
  57
  58 // print
  59 const PRINT = exp => pr_str(exp, true)
  60
  61 // repl
  62 let repl_env = new_env()
  63 const REP = str => PRINT(EVAL(READ(str), repl_env))
  64
  65 // core.EXT: defined using ES6
  66 for (let [k, v] of core_ns) { env_set(repl_env, Symbol.for(k), v) }
  67
  68 // core.mal: defined using language itself
  69 REP('(def! not (fn* (a) (if a false true)))')
  70
  71 while (true) {
  72     let line = readline('user> ')
  73     if (line == null) break
  74     try {
  75         if (line) { console.log(REP(line)) }
  76     } catch (exc) {
  77         if (exc instanceof BlankException) { continue }
  78         if (exc.stack) { console.log(exc.stack) }
  79         else           { console.log(`Error: ${exc}`) }
  80     }
  81 }