python/step8_macros.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 is_pair(x):
  14     return types._sequential_Q(x) and len(x) > 0
  15
  16 def quasiquote(ast):
  17     if not is_pair(ast):
  18         return types._list(types._symbol("quote"),
  19                            ast)
  20     elif ast[0] == 'unquote':
  21         return ast[1]
  22     elif is_pair(ast[0]) and ast[0][0] == 'splice-unquote':
  23         return types._list(types._symbol("concat"),
  24                            ast[0][1],
  25                            quasiquote(ast[1:]))
  26     else:
  27         return types._list(types._symbol("cons"),
  28                            quasiquote(ast[0]),
  29                            quasiquote(ast[1:]))
  30
  31 def is_macro_call(ast, env):
  32     return (types._list_Q(ast) and
  33             types._symbol_Q(ast[0]) and
  34             env.find(ast[0]) and
  35             hasattr(env.get(ast[0]), '_ismacro_'))
  36
  37 def macroexpand(ast, env):
  38     while is_macro_call(ast, env):
  39         mac = env.get(ast[0])
  40         ast = mac(*ast[1:])
  41     return ast
  42
  43 def eval_ast(ast, env):
  44     if types._symbol_Q(ast):
  45         return env.get(ast)
  46     elif types._list_Q(ast):
  47         return types._list(*map(lambda a: EVAL(a, env), ast))
  48     elif types._vector_Q(ast):
  49         return types._vector(*map(lambda a: EVAL(a, env), ast))
  50     elif types._hash_map_Q(ast):
  51         keyvals = []
  52         for k in ast.keys():
  53             keyvals.append(EVAL(k, env))
  54             keyvals.append(EVAL(ast[k], env))
  55         return types._hash_map(*keyvals)
  56     else:
  57         return ast  # primitive value, return unchanged
  58
  59 def EVAL(ast, env):
  60     while True:
  61         #print("EVAL %s" % printer._pr_str(ast))
  62         if not types._list_Q(ast):
  63             return eval_ast(ast, env)
  64
  65         # apply list
  66         ast = macroexpand(ast, env)
  67         if not types._list_Q(ast):
  68             return eval_ast(ast, env)
  69         if len(ast) == 0: return ast
  70         a0 = ast[0]
  71
  72         if "def!" == a0:
  73             a1, a2 = ast[1], ast[2]
  74             res = EVAL(a2, env)
  75             return env.set(a1, res)
  76         elif "let*" == a0:
  77             a1, a2 = ast[1], ast[2]
  78             let_env = Env(env)
  79             for i in range(0, len(a1), 2):
  80                 let_env.set(a1[i], EVAL(a1[i+1], let_env))
  81             ast = a2
  82             env = let_env
  83             # Continue loop (TCO)
  84         elif "quote" == a0:
  85             return ast[1]
  86         elif "quasiquote" == a0:
  87             ast = quasiquote(ast[1]);
  88             # Continue loop (TCO)
  89         elif 'defmacro!' == a0:
  90             func = types._clone(EVAL(ast[2], env))
  91             func._ismacro_ = True
  92             return env.set(ast[1], func)
  93         elif 'macroexpand' == a0:
  94             return macroexpand(ast[1], env)
  95         elif "do" == a0:
  96             eval_ast(ast[1:-1], env)
  97             ast = ast[-1]
  98             # Continue loop (TCO)
  99         elif "if" == a0:
 100             a1, a2 = ast[1], ast[2]
 101             cond = EVAL(a1, env)
 102             if cond is None or cond is False:
 103                 if len(ast) > 3: ast = ast[3]
 104                 else:            ast = None
 105             else:
 106                 ast = a2
 107             # Continue loop (TCO)
 108         elif "fn*" == a0:
 109             a1, a2 = ast[1], ast[2]
 110             return types._function(EVAL, Env, a2, env, a1)
 111         else:
 112             el = eval_ast(ast, env)
 113             f = el[0]
 114             if hasattr(f, '__ast__'):
 115                 ast = f.__ast__
 116                 env = f.__gen_env__(el[1:])
 117             else:
 118                 return f(*el[1:])
 119
 120 # print
 121 def PRINT(exp):
 122     return printer._pr_str(exp)
 123
 124 # repl
 125 repl_env = Env()
 126 def REP(str):
 127     return PRINT(EVAL(READ(str), repl_env))
 128
 129 # core.py: defined using python
 130 for k, v in core.ns.items(): repl_env.set(types._symbol(k), v)
 131 repl_env.set(types._symbol('eval'), lambda ast: EVAL(ast, repl_env))
 132 repl_env.set(types._symbol('*ARGV*'), types._list(*sys.argv[2:]))
 133
 134 # core.mal: defined using the language itself
 135 REP("(def! not (fn* (a) (if a false true)))")
 136 REP("(def! load-file (fn* (f) (eval (read-string (str \"(do \" (slurp f) \"\nnil)\")))))")
 137 REP("(defmacro! cond (fn* (& xs) (if (> (count xs) 0) (list 'if (first xs) (if (> (count xs) 1) (nth xs 1) (throw \"odd number of forms to cond\")) (cons 'cond (rest (rest xs)))))))")
 138
 139 if len(sys.argv) >= 2:
 140     REP('(load-file "' + sys.argv[1] + '")')
 141     sys.exit(0)
 142
 143 # repl loop
 144 while True:
 145     try:
 146         line = mal_readline.readline("user> ")
 147         if line == None: break
 148         if line == "": continue
 149         print(REP(line))
 150     except reader.Blank: continue
 151     except Exception as e:
 152         print("".join(traceback.format_exception(*sys.exc_info())))