python/step4_if_fn_do.py

   1 import sys, traceback
   2 import mal_readline
   3 import mal_types as types
   4 import reader, printer
   5 from env import Env
   6 import core
   7
   8 # read
   9 def READ(str):
  10     return reader.read_str(str)
  11
  12 # eval
  13 def eval_ast(ast, env):
  14     if types._symbol_Q(ast):
  15         return env.get(ast)
  16     elif types._list_Q(ast):
  17         return types._list(*map(lambda a: EVAL(a, env), ast))
  18     elif types._vector_Q(ast):
  19         return types._vector(*map(lambda a: EVAL(a, env), ast))
  20     elif types._hash_map_Q(ast):
  21         keyvals = []
  22         for k in ast.keys():
  23             keyvals.append(EVAL(k, env))
  24             keyvals.append(EVAL(ast[k], env))
  25         return types._hash_map(*keyvals)
  26     else:
  27         return ast  # primitive value, return unchanged
  28
  29 def EVAL(ast, env):
  30         #print("EVAL %s" % printer._pr_str(ast))
  31         if not types._list_Q(ast):
  32             return eval_ast(ast, env)
  33
  34         # apply list
  35         if len(ast) == 0: return ast
  36         a0 = ast[0]
  37
  38         if "def!" == a0:
  39             a1, a2 = ast[1], ast[2]
  40             res = EVAL(a2, env)
  41             return env.set(a1, res)
  42         elif "let*" == a0:
  43             a1, a2 = ast[1], ast[2]
  44             let_env = Env(env)
  45             for i in range(0, len(a1), 2):
  46                 let_env.set(a1[i], EVAL(a1[i+1], let_env))
  47             return EVAL(a2, let_env)
  48         elif "do" == a0:
  49             el = eval_ast(ast[1:], env)
  50             return el[-1]
  51         elif "if" == a0:
  52             a1, a2 = ast[1], ast[2]
  53             cond = EVAL(a1, env)
  54             if cond is None or cond is False:
  55                 if len(ast) > 3: return EVAL(ast[3], env)
  56                 else:            return None
  57             else:
  58                 return EVAL(a2, env)
  59         elif "fn*" == a0:
  60             a1, a2 = ast[1], ast[2]
  61             return types._function(EVAL, Env, a2, env, a1)
  62         else:
  63             el = eval_ast(ast, env)
  64             f = el[0]
  65             return f(*el[1:])
  66
  67 # print
  68 def PRINT(exp):
  69     return printer._pr_str(exp)
  70
  71 # repl
  72 repl_env = Env()
  73 def REP(str):
  74     return PRINT(EVAL(READ(str), repl_env))
  75
  76 # core.py: defined using python
  77 for k, v in core.ns.items(): repl_env.set(types._symbol(k), v)
  78
  79 # core.mal: defined using the language itself
  80 REP("(def! not (fn* (a) (if a false true)))")
  81
  82 # repl loop
  83 while True:
  84     try:
  85         line = mal_readline.readline("user> ")
  86         if line == None: break
  87         if line == "": continue
  88         print(REP(line))
  89     except reader.Blank: continue
  90     except Exception as e:
  91         print("".join(traceback.format_exception(*sys.exc_info())))