in reply to Re^3: top ten things every Perl hacker should know
in thread top ten things every Perl hacker should know

It's all right in front of you; in one sweep of your eye. The filtering, the modification, and the sorting (grep, map, sort, and maybe more). There aren't a couple sets of temporary variables and three or more bocks or subroutines to jump around and try to keep in your head at once. It's the same code condensed. I find it easier to read and much easier to debug.

So I do think the ST is a good example of elegance. I'm open to counter examples of what you consider Perl (not Python or Ruby of course!) elegance.

  • Comment on Re^4: top ten things every Perl hacker should know

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Re^5: top ten things every Perl hacker should know
by tilly (Archbishop) on Mar 17, 2006 at 07:05 UTC
    Let's take a list of files and use a Schwartzian Transform to sort it by file size descending, then alphabetical order ascending. 
    my @sorted_files
  = map {$_->[0]}
    sort {$b->[1] <=> $a->[1] or $a->[0] cmp $b->[0]}
    map {[$_, -s]} @files;

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    Here is the same code written as a normal sort. 
    my @sorted_files = sort {-s $b <=> -s $a or $a cmp $b} @files;

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    Clearly the Schwartzian Transform is more complex. But if you have a list of 1000 files, it's also about 10 times faster. Which is why we learn it.

    Now to explain my Ruby comment. In Ruby, arrays have a sort_by method. So in this example you'd write: 

    sorted_files = files.sort_by {|f| [- test(?s, f), f]};

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    and you've written the more efficient sort with less code than the regular sort. This does not work in Perl first of all because we don't have a sort_by method, and furthermore because Perl doesn't do anything useful when you try to sort array references. (Ruby sorts them lexicographically, with each field sorting in its "natural" way.)
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      We sort of have a sort_by method in Sort::Maker. But I've never liked the api. There is no denying that an ST is a scary sight to a new programmer not familiar with the idiom. I'd argue it should be wrapped in a sub for clarity most often.

      I like the PBP argument for using List::Util and List::MoreUtils functions such as any rather than idiomatic uses of grep. It makes your intention clear, and prevents you from thinking in syntax - no matter how comfortable and familiar that syntax is.

      update: added some words for clarity

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        We sort of have a sort_by method in Sort::Maker. But I've never liked the api

        you should try Sort::Key, it has a very simple API and it's faster and uses less memory than any other perl sorting technique: 

        use Sort::Key qw(keysort);
my @sorted = keysort { genkey($_) } @data;

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