Additional parentheses cause significant increase of parsing time

[treiher]

Parentheses have an unexpectedly high impact on the parsing time. Just by adding two pairs of parenthesis (without changing the semantics of the expression) the parsing time increased from 1 s to 53 s on my local machine.

from rflx.parser.grammar import mathematical_expression

mathematical_expression().parseString(" (Y / 9 - (3 / S -  (2 + G) )) ")  #  1 s
mathematical_expression().parseString(" (Y / 9 - (3 / S - ((2 + G)))) ")  #  7 s
mathematical_expression().parseString("((Y / 9 - (3 / S - ((2 + G)))))")  # 53 s

[treiher]

Enabling packrat parsing improves the performance significantly, so that the whole example shown above runs in less than 1 s.

[senier]

@treiher We had packrat off? Then I'm impressed that we had no more severe performance issues.

[treiher]

@treiher We had packrat off? Then I'm impressed that we had no more severe performance issues.

It's the default.

enablePackrat() - a class-level static method to enable a memoizing performance enhancement, known as “packrat parsing”. packrat parsing is disabled by default, since it may conflict with some user programs that use parse actions.