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This is just a toy grammar to test backtracking:
from pyparsing import *
a = Literal("a")
b = Literal("b")
c = Literal("c")
abb = a + b + b
abc = a + b + c
aba = a + b + a
grammar = MatchFirst( [ abb.setDebug(), abc.setDebug(), aba.setDebug() ] )
grammar.parseString( "aba" )
With packrat disabled, the returned parse tree
['a', 'b', 'a']
With packrat enabled, I get
['a', 'b', 'b', 'a']
Why is this happening, in the last case ? Thanks
This is a bug in pyparsing. Corrected version has been checked into SVN.