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     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       _default_:    f, args = eval_ast(ast, env)
  20                     return apply(f, args)
  21
  22 PRINT(exp): return printer.pr_str(exp)
  23
  24 repl_env = new Env()
  25 rep(str): return PRINT(EVAL(READ(str),repl_env))
  26
  27 repl_env.set('+, add_fn)
  28     ...
  29
  30 main loop:
  31   try:      println(rep(readline("user> ")))
  32   catch e:  println("Error: ", e)
  33
  34 --- env module ----------------------------------
  35 class Env (outer=null)
  36     data = hash_map()
  37   set(k,v): return data.set(k,v)
  38   find(k): return data.has(k) ? this : (if outer ? find(outer) : null)
  39   get(k): return data.find(k).get(k) OR raise "'" + k + "' not found"