process/step4_if_fn_do.txt

   1 --- step4_if_fn_do ------------------------------
   2 import types, reader, printer, env, core
   3
   4 READ(str): return reader.read_str(str)
   5
   6 eval_ast(ast,env):
   7   switch type(ast):
   8     symbol:      return env.get(ast)
   9     list,vector: return ast.map((x) -> EVAL(x,env))
  10     hash:        return ast.map((k,v) -> list(k, EVAL(v,env)))
  11     _default_:   return ast
  12
  13 EVAL(ast,env):
  14     if not list?(ast): return eval_ast(ast, env)
  15     if empty?(ast): return ast
  16     switch ast[0]:
  17       'def!:        return env.set(ast[1], EVAL(ast[2], env))
  18       'let*:        let_env = ...; return EVAL(ast[2], let_env)
  19       'do:          return eval_ast(rest(ast), env)[-1]
  20       'if:          return EVAL(EVAL(ast[1], env) ? ast[2] : ast[3], env)
  21       'fn*:         return (...a) -> EVAL(ast[2], new Env(env, ast[1], a))
  22       _default_:    f, args = eval_ast(ast, env)
  23                     return apply(f, args)
  24
  25 PRINT(exp): return printer.pr_str(exp)
  26
  27 repl_env = new Env()
  28 rep(str): return PRINT(EVAL(READ(str),repl_env))
  29
  30 ;; core.EXT: defined using Racket
  31 core.ns.map((k,v) -> (repl_env.set(k, v)))
  32
  33 ;; core.mal: defined using the language itself
  34 rep("(def! not (fn* (a) (if a false true)))")
  35
  36 main loop:
  37   try:      println(rep(readline("user> ")))
  38   catch e:  println("Error: ", e)
  39
  40 --- env module ----------------------------------
  41 class Env (outer=null,binds=[],exprs=[])
  42     data = hash_map()
  43     foreach b, i in binds:
  44       if binds[i] == '&: data[binds[i+1]] = exprs.drop(i); break
  45       else: data[binds[i]] = exprs[i]
  46   set(k,v): return data.set(k,v)
  47   find(k): return data.has(k) ? this : (if outer ? find(outer) : null)
  48   get(k): return data.find(k).get(k) OR raise "'" + k + "' not found"
  49
  50 --- core module ---------------------------------
  51 ns = {'=:        equal?,
  52
  53       'pr-str:   (a) -> a.map(|s| pr_str(e,true)).join(" ")),
  54       'str:      (a) -> a.map(|s| pr_str(e,false)).join("")),
  55       'prn:      (a) -> println(a.map(|s| pr_str(e,true)).join(" ")),
  56       'println:  (a) -> println(a.map(|s| pr_str(e,false)).join(" ")),
  57
  58       '<:        lt,
  59       '<=:       lte,
  60       '>:        gt,
  61       '>=:       gte,
  62       '+:        add,
  63       '-:        sub,
  64       '*:        mult,
  65       '/:        div,
  66
  67       'list:     list,
  68       'list?:    list?,
  69
  70       'empty?:   empty?,
  71       'count:    count}