process/step5_tco.txt

   1 --- step5_tco -----------------------------------
   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   while true:
  15     if not list?(ast): return eval_ast(ast, env)
  16     if empty?(ast): return ast
  17     switch ast[0]:
  18       'def!:        return env.set(ast[1], EVAL(ast[2], env))
  19       'let*:        env = ...; ast = ast[2] // TCO
  20       'do:          ast = eval_ast(ast[1..-1], env)[-1] // TCO
  21       'if:          EVAL(ast[1], env) ? ast = ast[2] : ast = ast[3] // TCO
  22       'fn*:         return new MalFunc(...)
  23       _default_:    f, args = eval_ast(ast, env)
  24                     if malfunc?(f): ast = f.fn; env = ... // TCO
  25                     else:           return apply(f, args)
  26
  27 PRINT(exp): return printer.pr_str(exp)
  28
  29 repl_env = new Env()
  30 rep(str): return PRINT(EVAL(READ(str),repl_env))
  31
  32 ;; core.EXT: defined using Racket
  33 core.ns.map((k,v) -> (repl_env.set(k, v)))
  34
  35 ;; core.mal: defined using the language itself
  36 rep("(def! not (fn* (a) (if a false true)))")
  37
  38 main loop:
  39   try:      println(rep(readline("user> ")))
  40   catch e:  println("Error: ", e)
  41
  42 --- env module ----------------------------------
  43 class Env (outer=null,binds=[],exprs=[])
  44     data = hash_map()
  45     foreach b, i in binds:
  46       if binds[i] == '&: data[binds[i+1]] = exprs.drop(i); break
  47       else: data[binds[i]] = exprs[i]
  48   set(k,v): return data.set(k,v)
  49   find(k): return data.has(k) ? this : (if outer ? find(outer) : null)
  50   get(k): return data.find(k).get(k) OR raise "'" + k + "' not found"
  51
  52 --- core module ---------------------------------
  53 ns = {'=:        equal?,
  54
  55       'pr-str:   (a) -> a.map(|s| pr_str(e,true)).join(" ")),
  56       'str:      (a) -> a.map(|s| pr_str(e,false)).join("")),
  57       'prn:      (a) -> println(a.map(|s| pr_str(e,true)).join(" ")),
  58       'println:  (a) -> println(a.map(|s| pr_str(e,false)).join(" ")),
  59
  60       '<:        lt,
  61       '<=:       lte,
  62       '>:        gt,
  63       '>=:       gte,
  64       '+:        add,
  65       '-:        sub,
  66       '*:        mult,
  67       '/:        div,
  68
  69       'list:     list,
  70       'list?:    list?,
  71
  72       'empty?:   empty?,
  73       'count:    count}