process/stepA_mal.txt

   1 --- stepA_mal -------------------------------
   2 import types, reader, printer, env, core
   3
   4 READ(str): return reader.read_str(str)
   5
   6 pair?(ast): return ... // true if non-empty sequence
   7 quasiquote(ast): return ... // quasiquote
   8
   9 macro?(ast, env): return ... // true if macro call
  10 macroexpand(ast, env): return ... // recursive macro expansion
  11
  12 eval_ast(ast,env):
  13   switch type(ast):
  14     symbol:      return env.get(ast)
  15     list,vector: return ast.map((x) -> EVAL(x,env))
  16     hash:        return ast.map((k,v) -> list(k, EVAL(v,env)))
  17     _default_:   return ast
  18
  19 EVAL(ast,env):
  20   while true:
  21     if not list?(ast): return eval_ast(ast, env)
  22
  23     ast = macroexpand(ast, env)
  24     if not list?(ast): return eval_ast(ast, env)
  25
  26     switch ast[0]:
  27       'def!:        return env.set(ast[1], EVAL(ast[2], env))
  28       'let*:        env = ...; ast = ast[2] // TCO
  29       'quote:       return ast[1]
  30       'quasiquote:  ast = quasiquote(ast[1]) // TCO
  31       'defmacro!:   return ... // like def!, but set macro property
  32       'macroexpand: return macroexpand(ast[1], env)
  33       'try*:        return ... // try/catch native and malval exceptions
  34       'do:          ast = eval_ast(ast[1..-1], env)[-1] // TCO
  35       'if:          EVAL(ast[1], env) ? ast = ast[2] : ast = ast[3] // TCO
  36       'fn*:         return new MalFunc(...)
  37       _default_:    f, args = eval_ast(ast, env)
  38                     if malfunc?(f): ast = f.fn; env = ... // TCO
  39                     else:           return apply(f, args)
  40
  41 PRINT(exp): return printer.pr_str(exp)
  42
  43 repl_env = new Env()
  44 rep(str): return PRINT(EVAL(READ(str),repl_env))
  45
  46 ;; core.EXT: defined using Racket
  47 core.ns.map((k,v) -> (repl_env.set(k, v)))
  48 repl_env.set('eval, (ast) -> EVAL(ast, repl-env))
  49 repl_env.set('*ARGV*, cmdline_args[1..])
  50
  51 ;; core.mal: defined using the language itself
  52 rep("(def! *host-language* \"racket\")")
  53 rep("(def! not (fn* (a) (if a false true)))")
  54 rep("(def! load-file (fn* (f) (eval (read-string (str \"(do \" (slurp f) \")\")))))")
  55 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)))))))");
  56 rep("(def! *gensym-counter* (atom 0))")
  57 rep("(def! gensym (fn* [] (symbol (str \"G__\" (swap! *gensym-counter* (fn* [x] (+ 1 x)))))))")
  58 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)))))))))")
  59
  60 if cmdline_args: rep("(load-file \"" + args[0] + "\")"); exit 0
  61
  62 rep("(println (str \"Mal [\" *host-language* \"]\"))")
  63 main loop:
  64   try:      println(rep(readline("user> ")))
  65   catch e:  println("Error: ", e)
  66
  67 --- env module ----------------------------------
  68 class Env (outer=null,binds=[],exprs=[])
  69     data = hash_map()
  70     foreach b, i in binds:
  71       if binds[i] == '&: data[binds[i+1]] = exprs.drop(i); break
  72       else: data[binds[i]] = exprs[i]
  73   set(k,v): return data.set(k,v)
  74   find(k): return data.has(k) ? this : (if outer ? find(outer) : null)
  75   get(k): return data.find(k).get(k) OR raise "'" + k + "' not found"
  76
  77 --- core module ---------------------------------
  78 ns = {'=:        equal?,
  79       'throw:    throw,
  80
  81       'nil?:     nil?,
  82       'true?:    true?,
  83       'false?:   false?,
  84       'symbol:   symbol,
  85       'symbol?:  symbol?,
  86       'keyword:  keyword,
  87       'keyword?: keyword?,
  88
  89       'pr-str:   (a) -> a.map(|s| pr_str(e,true)).join(" ")),
  90       'str:      (a) -> a.map(|s| pr_str(e,false)).join("")),
  91       'prn:      (a) -> println(a.map(|s| pr_str(e,true)).join(" ")),
  92       'println:  (a) -> println(a.map(|s| pr_str(e,false)).join(" ")),
  93       'read-string: read_str,
  94       'readline: readline,
  95       'slurp     read-file,
  96
  97       '<:        lt,
  98       '<=:       lte,
  99       '>:        gt,
 100       '>=:       gte,
 101       '+:        add,
 102       '-:        sub,
 103       '*:        mult,
 104       '/:        div,
 105       'time-ms   cur-epoch-millis,
 106
 107       'list:     list,
 108       'list?:    list?,
 109       'vector:   vector,
 110       'vector?:  vector?,
 111       'hash-map: hash_map,
 112       'map?:     hash_map?,
 113       'assoc:    assoc,
 114       'dissoc:   dissoc,
 115       'get:      get,
 116       'contains?: contains?,
 117       'keys:     keys,
 118       'vals:     vals,
 119
 120       'sequential? sequential?,
 121       'cons:     (a) -> concat([a[0]], a[1]),
 122       'concat:   (a) -> reduce(concat, [], a),
 123       'nth:      (a) -> a[0][a[1]] OR raise "nth: index out of range",
 124       'first:    (a) -> a[0][0] OR nil,
 125       'rest:     (a) -> a[0][1..] OR list(),
 126       'empty?:   empty?,
 127       'count:    count,
 128       'apply:    apply,
 129       'map:      map,
 130
 131       'conj:     conj,
 132
 133       'meta:     (a) -> a[0].meta,
 134       'with-meta: (a) -> a[0].with_meta(a[1]),
 135       'atom:     (a) -> new Atom(a[0]),
 136       'atom?:    (a) -> type(a[0]) == "atom",
 137       'deref:    (a) -> a[0].val,
 138       'reset!:   (a) -> a[0].val = a[1],
 139       'swap!:    swap!}