es6/step8_macros.mjs

   1 import rl from './node_readline.js'
   2 const readline = rl.readline
   3 import { _list_Q, _malfunc, _malfunc_Q } from './types'
   4 import { BlankException, read_str } from './reader'
   5 import { pr_str } from './printer'
   6 import { new_env, env_set, env_get } from './env'
   7 import { core_ns } from './core'
   8
   9 // read
  10 const READ = str => read_str(str)
  11
  12 // eval
  13 const is_pair = x => Array.isArray(x) && x.length > 0
  14
  15 const quasiquote = ast => {
  16     if (!is_pair(ast)) {
  17         return [Symbol.for('quote'), ast]
  18     } else if (ast[0] === Symbol.for('unquote')) {
  19         return ast[1]
  20     } else if (is_pair(ast[0]) && ast[0][0] === Symbol.for('splice-unquote')) {
  21         return [Symbol.for('concat'),
  22                 ast[0][1],
  23                 quasiquote(ast.slice(1))]
  24     } else {
  25         return [Symbol.for('cons'),
  26                 quasiquote(ast[0]),
  27                 quasiquote(ast.slice(1))]
  28     }
  29 }
  30
  31 function macroexpand(ast, env) {
  32     while (_list_Q(ast) && typeof ast[0] === 'symbol' && ast[0] in env) {
  33         let f = env_get(env, ast[0])
  34         if (!f.ismacro) { break }
  35         ast = f(...ast.slice(1))
  36     }
  37     return ast
  38 }
  39
  40
  41 const eval_ast = (ast, env) => {
  42     if (typeof ast === 'symbol') {
  43         return env_get(env, ast)
  44     } else if (ast instanceof Array) {
  45         return ast.map(x => EVAL(x, env))
  46     } else if (ast instanceof Map) {
  47         let new_hm = new Map()
  48         ast.forEach((v, k) => new_hm.set(EVAL(k, env), EVAL(v, env)))
  49         return new_hm
  50     } else {
  51         return ast
  52     }
  53 }
  54
  55 const EVAL = (ast, env) => {
  56   while (true) {
  57     //console.log('EVAL:', pr_str(ast, true))
  58     if (!_list_Q(ast)) { return eval_ast(ast, env) }
  59
  60     ast = macroexpand(ast, env)
  61     if (!_list_Q(ast)) { return eval_ast(ast, env) }
  62     if (ast.length === 0) { return ast }
  63
  64     const [a0, a1, a2, a3] = ast
  65     switch (typeof a0 === 'symbol' ? Symbol.keyFor(a0) : Symbol(':default')) {
  66         case 'def!':
  67             return env_set(env, a1, EVAL(a2, env))
  68         case 'let*':
  69             let let_env = new_env(env)
  70             for (let i=0; i < a1.length; i+=2) {
  71                 env_set(let_env, a1[i], EVAL(a1[i+1], let_env))
  72             }
  73             env = let_env
  74             ast = a2
  75             break // continue TCO loop
  76         case 'quote':
  77             return a1
  78         case 'quasiquote':
  79             ast = quasiquote(a1)
  80             break // continue TCO loop
  81         case 'defmacro!':
  82             let func = EVAL(a2, env)
  83             func.ismacro = true
  84             return env_set(env, a1, func)
  85         case 'macroexpand':
  86             return macroexpand(a1, env)
  87         case 'do':
  88             eval_ast(ast.slice(1,-1), env)
  89             ast = ast[ast.length-1]
  90             break // continue TCO loop
  91         case 'if':
  92             let cond = EVAL(a1, env)
  93             if (cond === null || cond === false) {
  94                 ast = (typeof a3 !== 'undefined') ? a3 : null
  95             } else {
  96                 ast = a2
  97             }
  98             break // continue TCO loop
  99         case 'fn*':
 100             return _malfunc((...args) => EVAL(a2, new_env(env, a1, args)),
 101                             a2, env, a1)
 102         default:
 103             let [f, ...args] = eval_ast(ast, env)
 104             if (_malfunc_Q(f)) {
 105                 env = new_env(f.env, f.params, args)
 106                 ast = f.ast
 107                 break // continue TCO loop
 108             } else {
 109                 return f(...args)
 110             }
 111     }
 112   }
 113 }
 114
 115 // print
 116 const PRINT = exp => pr_str(exp, true)
 117
 118 // repl
 119 let repl_env = new_env()
 120 const REP = str => PRINT(EVAL(READ(str), repl_env))
 121
 122 // core.EXT: defined using ES6
 123 for (let [k, v] of core_ns) { env_set(repl_env, Symbol.for(k), v) }
 124 env_set(repl_env, Symbol.for('eval'), a => EVAL(a, repl_env))
 125 env_set(repl_env, Symbol.for('*ARGV*'), [])
 126
 127 // core.mal: defined using language itself
 128 REP('(def! not (fn* (a) (if a false true)))')
 129 REP('(def! load-file (fn* (f) (eval (read-string (str "(do " (slurp f) ")")))))')
 130 REP('(defmacro! cond (fn* (& xs) (if (> (count xs) 0) (list \'if (first xs) (if (> (count xs) 1) (nth xs 1) (throw "odd number of forms to cond")) (cons \'cond (rest (rest xs)))))))')
 131 REP('(defmacro! or (fn* (& xs) (if (empty? xs) nil (if (= 1 (count xs)) (first xs) `(let* (or_FIXME ~(first xs)) (if or_FIXME or_FIXME (or ~@(rest xs))))))))')
 132
 133 if (process.argv.length > 2) {
 134     env_set(repl_env, Symbol.for('*ARGV*'), process.argv.slice(3))
 135     REP(`(load-file "${process.argv[2]}")`)
 136     process.exit(0)
 137 }
 138
 139
 140 while (true) {
 141     let line = readline('user> ')
 142     if (line == null) break
 143     try {
 144         if (line) { console.log(REP(line)) }
 145     } catch (exc) {
 146         if (exc instanceof BlankException) { continue }
 147         if (exc.stack) { console.log(exc.stack) }
 148         else           { console.log(`Error: ${exc}`) }
 149     }
 150 }