Hi all,
this is more of a generic lex question, but since plex doesn't support the flex
extension that could easily fix it, I'm asking here.
Take these lex rules:
--
%start INCOMLINE
%%
"//"start(INCOMLINE);
\n start(0);
.yymore;
[a-zA-Z_]([a-zA-Z0-9_])* return(ID);
--
The idea is that the comment start sequence "//" puts the lexer in the
INCOMLINE state, which eats everything until the next
newline, then goes back into the start state. This works for lines like that:
Foo//
But because lex picks the longest matching rule first, it won't work here:
Foo//Bar
"Bar" still gets parsed as an ID token, because the identifier rule is valid
for any state and considered longer.
Flex has Condition Scopes (see
http://dinosaur.compilertools.net/flex/flex_11.html near the end), where one
could just put all
generic rules in a "INITIAL only" scope. This is a bit awkward if one has to
write the prefix every time...
I have solved this in the past by including a mini scanner in the action
because comments are easy, but still... does anyone
have a better idea to do this right in the lexer?
--
Regards,
Martok
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