Two passes when only one is needed? about dart-petitparser HOT 1 CLOSED

The behavior you observe is correct, given the above grammar. The rule term succeeds parsing prod, but then fails to match the following + so it retries with the second part parsing prod. The same happens for the rule prod. The parens trigger this unfortunate behavior.

Normally this is not a big deal, but you can avoid it by rewriting the grammar (see https://github.com/petitparser/dart-petitparser/blob/master/test/petitparser_test.dart#L70) as:

term <- prod ( '+' prod)*
prod <- prim ('' prim)
prim <- '(' term ')' | num

Or you could use the helper that builds efficient expression parsers more easily: https://github.com/petitparser/dart-petitparser/blob/master/lib/src/petitparser/expression.dart

from dart-petitparser.