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adding support for shortest choice #28

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adding support for shortest choice #28

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40 changes: 37 additions & 3 deletions arpeggio/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,9 @@
DEFAULT_WS = '\t\n\r '
NOMATCH_MARKER = 0


class ShortestChoiceList(list):
pass

class ArpeggioError(Exception):
"""
Base class for arpeggio errors.
Expand Down Expand Up @@ -403,7 +405,37 @@ def _parse(self, parser):
parser._nm_raise(self, c_pos, parser)

return result

class ShortestChoice(Sequence):
def _parse(self, parser):
match = False
c_pos = parser.position
shortest_result = None
shortest_result_str = None
shortest_result_cpos = None
for e in self.nodes:
try:
result = e.parse(parser)
if result is not None:
result = [result]
result_str = "".join([x.flat_str() for x in flatten(result)])
if (not shortest_result) or (len(shortest_result_str) > len(result_str)):
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@igordejanovic igordejanovic Jun 2, 2016

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This can be done more optimal. Flattening and converting to string of all resulting subtrees is slow.
It is enough to use position and track in which branch you have smaller advance.

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@leiyangyou leiyangyou Jun 2, 2016

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I will make a patch for this

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@igordejanovic igordejanovic Jun 3, 2016

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Please make a unit test also if you can. I am trying to keep test coverage as high as possible. Thanks.

shortest_result = result
shortest_result_str = result_str
shortest_result_cpos = parser.position
match = True
parser.position = c_pos
except NoMatch as m:
parser.position = c_pos # Backtracking


if not match:
parser._nm_raise(self, c_pos, parser)

parser.position = shortest_result_cpos
return shortest_result

pass

class Repetition(ParsingExpression):
"""
Expand Down Expand Up @@ -1701,8 +1733,10 @@ def inner_from_python(expression):
if any((isinstance(x, CrossRef) for x in retval.nodes)):
__for_resolving.append(retval)

elif type(expression) in [list, tuple]:
if type(expression) is list:
elif type(expression) in [list, tuple, ShortestChoiceList]:
if type(expression) is ShortestChoiceList:
retval = ShortestChoice(expression)
elif type(expression) is list:
retval = OrderedChoice(expression)
else:
retval = Sequence(expression)
Expand Down