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Add in default_factory argument to Optional parser #18

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Add in default_factory argument to Optional parser #18

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8 changes: 5 additions & 3 deletions parcon/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1347,20 +1347,22 @@ def __repr__(self):
class Optional(_GRParser):
"""
A parser that returns whatever its underlying parser returns, except that
if the specified parser fails, this parser succeeds and returns the default
if the specified parser fails, this parser succeeds and either invokes the
default_factory callable, returning the result, or returns the default
result specified to it (which, itself, defaults to None).
"""
def __init__(self, parser, default=None):
def __init__(self, parser, default=None, default_factory=None):
self.parser = parser
self.default = default
self.default_factory = default_factory or (lambda: default)
self.railroad_children = [self.parser]

def parse(self, text, position, end, space):
result = self.parser.parse(text, position, end, space)
if result:
return result
else:
return match(position, self.default, result.expected)
return match(position, self.default_factory(), result.expected)

def do_graph(self, graph):
graph.add_node(id(self), label="Optional, defaulting to:\n%s" % repr(self.default))
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