I said I'd use unless( complex expression ) over if( ! ( complex expression ) ) so your argument doesn't apply since the if( ! ( complex expression ) ) would require the same translation under the same circumstances.

Whether it makes more sense to distribute the "not" inside of the complex expression depends on a lot of things. 

    # unless object is valid and either isn't busy or can wait:
    unless(  $a  &&  ref($a)  &&  isa($a,'Foo')
         &&  (  ! $a->IsBusy()  ||  $a->CanWait()  )  ) {
        return;
    }

[download]
is clearer to me than: 
    # if object is not valid or both is busy and can't wait:
    if(  ! $a  ||  ! ref($a)  ||  ! isa($a,'Foo')
     ||  $a->IsBusy()  &&  ! $a->CanWait()  ) {
        return;
    }

[download]
and I don't understand why you (seem to) think that unless can't be understood without translating it into if. I'd only use unless in a case where it makes the meaning clearer.

For simple cases, I find that the difference in clarity is minimal and so prefer the consistancy of always using if. As a statement modifier, unless sometimes reads more naturally. As a conditional block, the benefit of unless only becomes worthwhile to me when the expression is complex enough that factoring out the negation can make a relatively big difference in the clarity of the code.

        - tye (but my friends call me "Tye")

In reply to (tye)Re4: mapcar -- map for more than one list by tye
in thread mapcar -- map for more than one list by tye

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.