[antlr-interest] uh oh...trouble in meaning of (..)=> pred!!!
antlr at mirality.co.nz
Thu Mar 15 12:18:04 PDT 2007
At 07:16 16/03/2007, Terence Parr wrote:
>Hi. I believe a PEG would do
>a b &c &d
>using & predicates that match but don't consume.
Actually thinking on it a bit more, I wonder if using a "!!"
suffix might be more appropriate (as in "a b c!! d!!"). That way,
one ! means "match, consume, but don't output", and two !s means
"match, don't consume, and don't output".
(I still think ! should work in the lexer, though, even if only as
a prefix/suffix for performance reasons. That's the most common
>Auto backtracking will do the optimal "use synpred only if
>fails", but (...)=> manual predicates will force backtracking to
>eval the pred. I can't know what's inside compared to alt
>whereas with auto backtracking pred is copy of alt.
Oh, right, you have to avoid executing actions while in a path
that can potentially backtrack, so they need to be gone through
twice. Forgot about that.
More information about the antlr-interest