G'day lightoverhead,

I ran that code and got the same result as you: 

$ perl -Mstrict -Mwarnings -E '
    "abcdef" =~ / .+ (?{say "Matched so far: $&"}) bcdef $/x;
'
Matched so far: a

[download]

I then stepped through the code using Regexp::Debugger: 

$ perl -Mstrict -Mwarnings -E '
    use Regexp::Debugger;
    "abcdef" =~ / .+ (?{say "Matched so far: $&"}) bcdef $/x;
'

[download]

This showed each of the six "Matched so far: ..." lines in the same order as you have them. It also showed backtracking behaviour as I, and presumably you, would expect.

The problem seems to lie with just the output; however, I don't know what that problem is.

-- Ken

In reply to Re: Interesting behavior of regular expression engine by kcott
in thread Interesting behavior of regular expression engine by lightoverhead

Title:
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, details, 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, summary, 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.