process/step2_eval.txt

   1 --- step2_eval ----------------------------------
   2 import types, reader, printer
   3
   4 READ(str): return reader.read_str(str)
   5
   6 eval_ast(ast,env):
   7   switch type(ast):
   8     symbol:      return lookup(env, ast) OR raise "'" + ast + "' not found"
   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     f, args = eval_ast(ast, env)
  17     return apply(f, args)
  18
  19 PRINT(exp): return printer.pr_str(exp)
  20
  21 repl_env = {'+: add_fn, ...}
  22 rep(str): return PRINT(EVAL(READ(str),repl_env))
  23
  24 main loop:
  25   try:      println(rep(readline("user> ")))
  26   catch e:  println("Error: ", e)