Beefy Boxes and Bandwidth Generously Provided by pair Networks
Do you know where your variables are?

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
For manually writing lexers my favorite idiom is $$s =~ m/\G.../gc. In scalar context it permits to advance in a string $$s I want to lex. If it matches the current position, it moves past the match, if not, the position is inchanged, \G permits to anchor the match at the current position. I could also use $$s = s/^...//. It does not cost much because the implementation does not move the string to truncate but just move an internal pointer. But this is immaterial to the following discussion.

A lexer for Parse::Yapp ends up looking like

sub lexer { my($parser)=shift; my $s = $parser->YYData->{INPUT}; # reference to the string to lex m/\G\s+/gc; skip any spaces return ('INT', $1) if $$s =~ m/\G\(d+)/gc; return ('ID', $1) if $$s =~ m/\G([A-Z]\w*)/gc; ... # and it goes on for many tentative matches }
I know that I always match on $$s so why should I restate it at each match. I _had_ to remove these useless $$S !

It took me a long time to realize that I could do it with a typeglob trick :

*_ = $parser->YYData->{INPUT}; # reference to the string to lex
Now $_ is an alias to the string to lex. So I can match on it I and don't need the =~ operator anymore

-- stefp

In reply to when $$s =~ m/\G.../gc is too verbose by stefp

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?

    What's my password?
    Create A New User
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others cooling their heels in the Monastery: (4)
    As of 2020-11-30 08:34 GMT
    Find Nodes?
      Voting Booth?

      No recent polls found