At 06:53 13/01/2009, Brisard, Fred D wrote:
>I am parsing a grammar that uses minus or plus at the end of line
>to indicate a continuation.
[...]
>I would like to just absorb them into the hidden stream so that
>the input appears to be on a single line.
>
>If I wanted to make a first pass on the input and just absorb
>'-\n' and '+\n' then all would be well. That seems pretty
>wasteful to make a pass to just do that. It seems like I should
>be able to do it during the lexical pass.
You can; you just need to give the lexer enough hinting so that it
can cope with both cases properly:
MINUS: '-' ('\r'? '\n' { skip(); })?;
PLUS: '+' ('\r'? '\n' { skip(); })?;
(Or instead of skipping, you could change the $type to
CONTINUATION and the $channel to HIDDEN.)
You will also need to ensure that '-' and '+' won't be consumed by
other lexer rules (or at least that if they are, it's in contexts
where a continuation isn't permitted). And your parser will have
to be able to cope with getting MINUS and PLUS tokens between
other tokens.
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