Add gensym and clean `or` macro to stepA of 19 implementations (part 3)

[jackhill/mal.git] / es6 / stepA_mal.js

import { readline } from './node_readline'
import { _symbol, _symbol_Q, _list_Q, _vector, _vector_Q,
         _hash_map_Q, _sequential_Q, _malfunc, _malfunc_Q } from './types'
import { BlankException, read_str } from './reader'
import { pr_str } from './printer'
import { new_env, env_set, env_get } from './env'
import { core_ns } from './core'

// read
const READ = (str) => read_str(str)

// eval
const is_pair = x => _sequential_Q(x) && x.length > 0

const quasiquote = ast => {
    if (!is_pair(ast)) {
        return [_symbol('quote'), ast]
    } else if (ast[0] === _symbol('unquote')) {
        return ast[1]
    } else if (is_pair(ast[0]) && ast[0][0] === _symbol('splice-unquote')) {
        return [_symbol('concat'), ast[0][1], quasiquote(ast.slice(1))]
    } else {
        return [_symbol('cons'), quasiquote(ast[0]), quasiquote(ast.slice(1))]
    }
}

function is_macro_call(ast, env) {
    return _list_Q(ast) &&
           _symbol_Q(ast[0]) &&
           ast[0] in env &&
           env_get(env, ast[0]).ismacro
}

function macroexpand(ast, env) {
    while (is_macro_call(ast, env)) {
        let mac = env_get(env, ast[0])
        ast = mac(...ast.slice(1))
    }
    return ast
}


const eval_ast = (ast, env) => {
    if (_symbol_Q(ast)) {
        return env_get(env, ast)
    } else if (_list_Q(ast)) {
        return ast.map((x) => EVAL(x, env))
    } else if (_vector_Q(ast)) {
        return _vector(...ast.map((x) => EVAL(x, env)))
    } else if (_hash_map_Q(ast)) {
        let new_hm = new Map()
        for (let [k, v] of ast) {
            new_hm.set(EVAL(k, env), EVAL(v, env))
        }
        return new_hm
    } else {
        return ast
    }
}

const EVAL = (ast, env) => {
  while (true) {
    //console.log('EVAL:', pr_str(ast, true))
    if (!_list_Q(ast)) { return eval_ast(ast, env) }

    ast = macroexpand(ast, env)
    if (!_list_Q(ast)) { return ast; }

    const [a0, a1, a2, a3] = ast
    const a0sym = _symbol_Q(a0) ? Symbol.keyFor(a0) : Symbol(':default')
    switch (a0sym) {
        case 'def!': 
            return env_set(env, a1, EVAL(a2, env))
        case 'let*':
            let let_env = new_env(env)
            for (let i=0; i < a1.length; i+=2) {
                env_set(let_env, a1[i], EVAL(a1[i+1], let_env))
            }
            env = let_env
            ast = a2
            break; // continue TCO loop
        case 'quote':
            return a1
        case 'quasiquote':
            ast = quasiquote(a1)
            break; // continue TCO loop
        case 'defmacro!':
            let func = EVAL(a2, env)
            func.ismacro = true
            return env_set(env, a1, func)
        case 'macroexpand':
            return macroexpand(a1, env)
        case 'try*':
            try {
                return EVAL(a1, env)
            } catch (exc) {
                if (a2 && a2[0] === _symbol('catch*')) {
                    if (exc instanceof Error) { exc = exc.message; }
                    return EVAL(a2[2], new_env(env, [a2[1]], [exc]))
                } else {
                    throw exc
                }
            }
        case 'do':
            eval_ast(ast.slice(1,-1), env)
            ast = ast[ast.length-1]
            break; // continue TCO loop
        case 'if':
            let cond = EVAL(a1, env)
            if (cond === null || cond === false) {
                ast = (typeof a3 !== 'undefined') ? a3 : null
            } else {
                ast = a2
            }
            break; // continue TCO loop
        case 'fn*':
            return _malfunc((...args) => EVAL(a2, new_env(env, a1, args)),
                    a2, env, a1)
        default:
            let [f, ...args] = eval_ast(ast, env)
            if (_malfunc_Q(f)) {
                env = new_env(f.env, f.params, args)
                ast = f.ast
                break; // continue TCO loop
            } else {
                return f(...args)
            }
    }
  }
}

// print
const PRINT = (exp) => pr_str(exp, true)

// repl
let repl_env = new_env()
const REP = (str) => PRINT(EVAL(READ(str), repl_env))

// core.EXT: defined using ES6
for (let [k, v] of core_ns) { env_set(repl_env, _symbol(k), v) }
env_set(repl_env, _symbol('eval'), a => EVAL(a, repl_env))
env_set(repl_env, _symbol('*ARGV*'), [])

// core.mal: defined using language itself
REP('(def! *host-language* "ecmascript6")')
REP('(def! not (fn* (a) (if a false true)))')
REP('(def! load-file (fn* (f) (eval (read-string (str "(do " (slurp f) ")")))))')
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)))))))')
REP('(def! *gensym-counter* (atom 0))')
REP('(def! gensym (fn* [] (symbol (str \"G__\" (swap! *gensym-counter* (fn* [x] (+ 1 x)))))))')
REP('(defmacro! or (fn* (& xs) (if (empty? xs) nil (if (= 1 (count xs)) (first xs) (let* (condvar (gensym)) `(let* (~condvar ~(first xs)) (if ~condvar ~condvar (or ~@(rest xs)))))))))')

if (process.argv.length > 2) { 
    env_set(repl_env, '*ARGV*', process.argv.slice(3))
    REP(`(load-file "${process.argv[2]}")`)
    process.exit(0)
}

REP('(println (str "Mal [" *host-language* "]"))')
while (true) {
    let line = readline('user> ')
    if (line == null) break
    try {
        if (line) { console.log(REP(line)); }
    } catch (exc) {
        if (exc instanceof BlankException) { continue; }
        if (exc.stack) { console.log(exc.stack); }
        else           { console.log(`Error: ${exc}`); }
    }
}