process/step8_macros.txt

   1 --- step8_macros --------------------------------
   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     if empty?(ast): return ast
  26
  27     switch ast[0]:
  28       'def!:        return env.set(ast[1], EVAL(ast[2], env))
  29       'let*:        env = ...; ast = ast[2] // TCO
  30       'quote:       return ast[1]
  31       'quasiquote:  ast = quasiquote(ast[1]) // TCO
  32       'defmacro!:   return ... // like def!, but set macro property
  33       'macroexpand: return macroexpand(ast[1], env)
  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! not (fn* (a) (if a false true)))")
  53 rep("(def! load-file (fn* (f) (eval (read-string (str \"(do \" (slurp f) \"\nnil)\")))))")
  54 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)))))))");
  55
  56 if cmdline_args: rep("(load-file \"" + args[0] + "\")"); exit 0
  57
  58 main loop:
  59   try:      println(rep(readline("user> ")))
  60   catch e:  println("Error: ", e)
  61
  62 --- env module ----------------------------------
  63 class Env (outer=null,binds=[],exprs=[])
  64     data = hash_map()
  65     foreach b, i in binds:
  66       if binds[i] == '&: data[binds[i+1]] = exprs.drop(i); break
  67       else: data[binds[i]] = exprs[i]
  68   set(k,v): return data.set(k,v)
  69   find(k): return data.has(k) ? this : (if outer ? find(outer) : null)
  70   get(k): return data.find(k).get(k) OR raise "'" + k + "' not found"
  71
  72 --- core module ---------------------------------
  73 ns = {'=:        equal?,
  74
  75       'pr-str:   (a) -> a.map(|s| pr_str(e,true)).join(" ")),
  76       'str:      (a) -> a.map(|s| pr_str(e,false)).join("")),
  77       'prn:      (a) -> println(a.map(|s| pr_str(e,true)).join(" ")),
  78       'println:  (a) -> println(a.map(|s| pr_str(e,false)).join(" ")),
  79       'read-string: read_str,
  80       'slurp     read-file,
  81
  82       '<:        lt,
  83       '<=:       lte,
  84       '>:        gt,
  85       '>=:       gte,
  86       '+:        add,
  87       '-:        sub,
  88       '*:        mult,
  89       '/:        div,
  90
  91       'list:     list,
  92       'list?:    list?,
  93
  94       'cons:     (a) -> concat([a[0]], a[1]),
  95       'concat:   (a) -> reduce(concat, [], a),
  96       'nth:      (a) -> a[0][a[1]] OR raise "nth: index out of range",
  97       'first:    (a) -> a[0][0] OR nil,
  98       'rest:     (a) -> a[0][1..] OR list(),
  99       'empty?:   empty?,
 100       'count:    count,
 101
 102       'atom:     (a) -> new Atom(a[0]),
 103       'atom?:    (a) -> type(a[0]) == "atom",
 104       'deref:    (a) -> a[0].val,
 105       'reset!:   (a) -> a[0].val = a[1],
 106       'swap!:    swap!}