Problem Combining Operator | and Operator +

[xie-dongping]

Consider the following simple and fictive example:

from funcparserlib.parser import many, some, finished

code = "aa"

p1 = some(lambda x: x == 'a')
p2 = many(p1)

p_or = p1 | p2

parsed_tokens = (p3+finished).parse("aa") 
# Error, since it would short-circuit to p1!

I encounter the case when writing a toy parser for a modeling language.

I'm not really familiar with the parsing theory, so I was wondering if this is the intended behavior for a parser combinator?

If it is not, how may I fix the __or__ method of the Parser class (maybe even more)? I thought about propagating the exceptions back to the __or__ method, or maybe you would have a better idea?

[xie-dongping]

I understand that the grammar defined above is ambiguous, and it is only used to illustrate the point, that I understand the or operator in a different way.

[vlasovskikh]

@xie-dongping Infinite left recursion is a known problem. There is an experimental branch declarative-api where I've added, among other things, automatic detection of left recursion that shows the problematic piece of your grammar. See also the description of the problem in the docs.

[xie-dongping]

Thank you for the reference! I've also solved my problem!