python/step2_eval.py

   1 import sys, traceback
   2 import mal_readline
   3 import mal_types as types
   4 import reader, printer
   5
   6 # read
   7 def READ(str):
   8     return reader.read_str(str)
   9
  10 # eval
  11 def eval_ast(ast, env):
  12     if types._symbol_Q(ast):
  13         try:
  14             return env[ast]
  15         except:
  16             raise Exception("'" + ast + "' not found")
  17     elif types._list_Q(ast):
  18         return types._list(*map(lambda a: EVAL(a, env), ast))
  19     elif types._vector_Q(ast):
  20         return types._vector(*map(lambda a: EVAL(a, env), ast))
  21     elif types._hash_map_Q(ast):
  22         keyvals = []
  23         for k in ast.keys():
  24             keyvals.append(EVAL(k, env))
  25             keyvals.append(EVAL(ast[k], env))
  26         return types._hash_map(*keyvals)
  27     else:
  28         return ast  # primitive value, return unchanged
  29
  30 def EVAL(ast, env):
  31         #print("EVAL %s" % printer._pr_str(ast))
  32         if not types._list_Q(ast):
  33             return eval_ast(ast, env)
  34
  35         # apply list
  36         el = eval_ast(ast, env)
  37         f = el[0]
  38         return f(*el[1:])
  39
  40 def PRINT(exp):
  41     return printer._pr_str(exp)
  42
  43 # repl
  44 repl_env = {}
  45 def REP(str):
  46     return PRINT(EVAL(READ(str), repl_env))
  47
  48 repl_env['+'] = lambda a,b: a+b
  49 repl_env['-'] = lambda a,b: a-b
  50 repl_env['*'] = lambda a,b: a*b
  51 repl_env['/'] = lambda a,b: int(a/b)
  52
  53 # repl loop
  54 while True:
  55     try:
  56         line = mal_readline.readline("user> ")
  57         if line == None: break
  58         if line == "": continue
  59         print(REP(line))
  60     except reader.Blank: continue
  61     except Exception as e:
  62         print("".join(traceback.format_exception(*sys.exc_info())))