process/step3_env.txt

   1 --- step3_env -----------------------------------
   2 import types, reader, printer, env
   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     switch ast[0]:
  16       'def!:        return env.set(ast[1], EVAL(ast[2], env))
  17       'let*:        let_env = ...; return EVAL(ast[2], let_env)
  18       _default_:    f, args = eval_ast(ast, env)
  19                     return apply(f, args)
  20
  21 PRINT(exp): return printer.pr_str(exp)
  22
  23 repl_env = new Env()
  24 rep(str): return PRINT(EVAL(READ(str),repl_env))
  25
  26 repl_env.set('+, add_fn)
  27     ...
  28
  29 main loop:
  30   try:      println(rep(readline("user> ")))
  31   catch e:  println("Error: ", e)
  32
  33 --- env module ----------------------------------
  34 class Env (outer=null)
  35     data = hash_map()
  36   set(k,v): return data.set(k,v)
  37   find(k): return data.has(k) ? this : (if outer ? find(outer) : null)
  38   get(k): return data.find(k).get(k) OR raise "'" + k + "' not found"