Purists are theorists, not do-orists. I'm a do-orist. Let's say I have a N-tree of objects and some function that walks the tree and executes itself on each child of a given node. Now, I want to stop walking the tree if any child returns 0 instead of 1. 
# Impure
sub walk_and_do
{
    my $self = shift;

    foreach my $child (@{$self->children})
    {
        return 0 unless $child->walk_and_do;
    }

    return 0 unless $self->do_my_stuff;

    return 1;
}

#####

# Pure
sub walk_and_do
{
    my $self = shift;

    my $rc = 1;
    foreach my $child (@{$self->children})
    {
        $rc = $child->walk_and_do;
        last unless $rc;
    }

    unless ($rc)
    {
        $rc = $self->do_my_stuff;
    }

    return $rc;
}

[download]
I think that the first is clearer and cleaner. There are less levels of indentation. Torvalds says in his style guide that there should never be more than 3 levels of indentation. If you're constantly checking codes and values, that simply won't work. I often find it harder to read code with 1 entry and 1 exit vs. 1 entry and N intelligently-designed exits.

Exit when appropriate, not when some schmuck with a bunch of letters after their name tells you. I work for a living.

------
We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.

In reply to Re3: A matter of style by dragonchild
in thread A matter of style by Ryszard

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.