--- Dave Whipp <[EMAIL PROTECTED]> wrote:
> "Piers Cawley" <[EMAIL PROTECTED]> wrote
> > Parsers with Pre-processors
> > I didn't quite understand what Dave Whipp was driving at when
> > he talked about overloading the "<ws>" pattern as a way of doing
> > preprocessing of Perl 6 patterns. I didn't understand Luke
> > Palmer's answer either. Help.
>
> Let me see if I can clarify a bit.
...
> I believe that an obvious inference is that :w processing should
> include the preprocessor parsing. Then the issue becomes one of
> mechanism: how do we tell :w what our (complex) definition of
> whitespace is; and how to we implement the preprocessor commands
> to modify the input-stream to the regex engine. Even though I'm not
> sure that my original answers are correct (perhaps some form of
> C<temp> would be a better approach), I'll refer you back to my
> original post (and Luke's reply) for those details. I also need
> to think about how C-macros would be implemented.
>
Actually, IMO this goes back to the conversation we had some time about
about being able to run grammars/patterns against arbitrary objects.
What you really want is to be able to "chain" grammars:
> my $fh = open "<hello.c";
> $fh =~ /<Grammars::Languages::C>/;
grammar Grammars::Languages::C {
method init {
SUPER::init;
$.source = (new Grammars::Language::C::Preprocessor).open($source);
}
...
}
grammar Grammars::Languages::C::Preprocessor {
rule CompilationUnit {
( <Directive> | <UnprocessedStuff> )*
}
rule Directive {
<Hash> ( Include
| Line
| Conditional
| Define
) <Continuation>*
}
rule Hash { /^\s*#\s*/ }
rule Include {...}
rule Line {...}
rule Conditional {...}
rule Define {...}
rule Continuation {...}
rule UnprocessedStuff {...}
}
Except that it would probably be even better to do this arbitrarily.
> my $fh = open "<hello.c";
> $fh =~ /<Grammars::Languages::C>/;
$fh =~ /<Grammars::Languages::C(input_method =
Grammars::Languages::C::Preprocessor)>/;
(Of course, in reality the C grammar would automatically use the
preprocessor as its input method without having to be told. But it
should be able to do so as two separate grammars.)
Likewise:
my $fh = open "<perl.1.gz";
$fh =~ /<Grammars::Languages::Runoff::Nroff(input_method
= Grammars::Languages::Runoff::tbl(input_method
= Grammars::Language::Runoff::eqn(input_method
= IO::Gunzip)))>/;
=Austin
