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Re: Grammar doesn't seem to match any token

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From:
Patrick R. Michaud
Date:
September 24, 2018 00:13
Subject:
Re: Grammar doesn't seem to match any token
Message ID:
20180924001308.GA31763@pmichaud.com
I suspect the rule:

    rule other { .  }

means that in

    $input = '~i <<<YZ';
    my $w = Weaver.new();
    Weave.parse($input, :actions($w));

the "other" rule cannot match the "Y" or the "Z" because there would need to be a space between them.  The use of "rule" as a regex declarator implies that spaces in the regex source are :sigspace, which means that whitespace in the rule prevents two word characters from being adjacent at that point and any available whitespace is consumed.

Change "rule" to "token" on these rules and I suspect you'll get <other> to match (although <other> will also end up matching the space after the "i" in the text string, since white spaces are no longer significant).  Or try just changing the <other> rule to be a token and leave the others as rules.

Phrased another way, the <other> rule as written now is roughly equivalent to writing

   token other { . <!ww> \s* }

which will match a word character only when it's not immediately followed by another word character.

Pm


On Sun, Sep 23, 2018 at 08:01:31PM -0400, yary wrote:
> Let's see.
> 
> If you have my $input = '~i o<<<', then <other> matches.
> 
>  'rule' turns on :sigspace. If you use 'token' instead of 'rule' then
> <other> matches.
> 
> I don't quite have the full picture of what's happening.
> 
> -y
> 
> On Sun, Sep 23, 2018 at 7:07 PM, Mark Carter <alt.mcarter@gmail.com> wrote:
> 
> > My grammar doesn't seem to match the 'other' rule. What's wrong with it?
> >
> > grammar Weave {
> >         token TOP {  <el> * }
> >         rule el {  <lt> | <tilde> | <other>  }
> >         rule lt { '<'  }
> >         rule tilde { '~' \S+ }
> >         rule other { .  }
> > }
> >
> > class Weaver {
> >         has Str $.outstr;
> >
> >         method TOP   ($/) { make $<el> ; put("top called") ; put($<el>) }
> >         method el    ($/) { put($/) }
> >         method tilde ($/) { say 'tilde called' }
> >         method lt    ($/) { make '&lt;' ; put('&lt'); $!outstr ~= 'X' }
> >         method other ($/) { $!outstr ~= '.'; say 'other called'; put('.');
> > }
> >
> > }
> >
> > $input = '~i <<<YZ';
> > my $w = Weaver.new();
> > Weave.parse($input, :actions($w));
> > say $w.outstr; # outputs XXX
> >
> > It never once says 'other called'. It seems to be matching the '<' signs
> > OK, and I think the '~' is OK, too. It's just any other token that it's not
> > matching.
> >

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