Beefy Boxes and Bandwidth Generously Provided by pair Networks
We don't bite newbies here... much
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??
Sometimes while(...) magically deparsed to while(defined(...)), but sometimes it doesn't. How is this decision made?
#### GLOBS cause defined to show up # while(<*.pl>) {} DEFINEDNESS % perl -MO=Deparse -e 'while(<*.pl>) {}' while (defined($_ = CORE::GLOBAL::glob('*.pl', 0))) { (); } # 1 while (<*.pl>) DEFINEDNESS % perl -MO=Deparse -e '1 while(<*.pl>)' '???' while defined($_ = CORE::GLOBAL::glob('*.pl', 0)); #### Simple vars dont # while($x) {} TRUTHFULNESS % perl -MO=Deparse -e 'while($x) {}' while ($x) { (); } # '1 while($x)' TRUTHFULNESS % perl -MO=Deparse -e '1 while($x)' '???' while $x; #### Why do these two behave differently???? # 'while($x = <*.pl>) {} DEFINEDNESS % perl -MO=Deparse -e 'while($x = <*.pl>) {}' while (defined($x = CORE::GLOBAL::glob('*.pl', 0))) { (); } # '1 while($x = <*.pl>) TRUTHFULNESS % perl -MO=Deparse -e '1 while($x = <*.pl>)' '???' while $x = CORE::GLOBAL::glob('*.pl', 0);
I looked for documentation on this behaviour but couldn't find any. Flow control keywords aren't listed in perlfunc, do they have their own perldoc page?

-Blake


In reply to When does while() test for defined vs truth by blakem

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!
  • 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
  • Outside of code tags, you may need to use entities for some characters:
            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?
    Username:
    Password:

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

    How do I use this? | Other CB clients
    Other Users?
    Others making s'mores by the fire in the courtyard of the Monastery: (3)
    As of 2014-09-19 01:09 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      How do you remember the number of days in each month?











      Results (129 votes), past polls