Created
November 22, 2012 20:01
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tail call optimization decorator
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import sys | |
def tail_recursion_with_stack_inspection(g): | |
''' | |
Version of tail_recursion decorator using stack-frame inspection. | |
''' | |
loc_vars ={"in_loop":False,"cnt":0} | |
def result(*args, **kwd): | |
if not loc_vars["in_loop"]: | |
loc_vars["in_loop"] = True | |
while 1: | |
tc = g(*args,**kwd) | |
try: | |
qual, args, kwd = tc | |
if qual == 'continue': | |
continue | |
except TypeError: | |
loc_vars["in_loop"] = False | |
return tc | |
else: | |
f = sys._getframe() | |
if f.f_back and f.f_back.f_back and \ | |
f.f_back.f_back.f_code == f.f_code: | |
return ('continue',args, kwd) | |
return g(*args,**kwd) | |
return result | |
def tail_recursion(g): | |
''' | |
Version of tail_recursion decorator using no stack-frame inspection. | |
''' | |
loc_vars ={"in_loop":False,"cnt":0} | |
def result(*args, **kwd): | |
loc_vars["cnt"]+=1 | |
if not loc_vars["in_loop"]: | |
loc_vars["in_loop"] = True | |
while 1: | |
tc = g(*args,**kwd) | |
try: | |
qual, args, kwd = tc | |
if qual == 'continue': | |
continue | |
except (TypeError, ValueError): | |
loc_vars["in_loop"] = False | |
return tc | |
else: | |
if loc_vars["cnt"]%2==0: | |
return ('continue',args, kwd) | |
else: | |
return g(*args,**kwd) | |
return result |
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