Re: Currying--useful examples?

Another typical example involves higher-level functions like map. If map in Perl were curried then I could say something like:

# contrived
my $incAll = map { $_++ };
my @data = return_some_numbers();
my @data2 = return_some_other_numbers();
$incAll->(@data);
$incAll->(@data2);
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and now I would have both of my arrays incremented by 1 across all their elements. Better yet, I could combine it with closures to create incrementors by an arbitrary value:

sub makeIncr {
  my $incr = $_[0];
  return map { $_ += $incr };
}
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In my own experience, I use currying and partial invokation extensively in Haskell which has native syntactic support for them, but so far I have not really come across them in my own Perl work.

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Re^2: Currying--useful examples? by tsee (Curate) on Jan 11, 2007 at 08:34 UTC
It's really quite simple to write a curry-able map in Perl. I'd expect it to be pretty slow, though, because of the many subroutine calls: 2+n for a list of n elements. If "map CODE, LIST" treats CODE as a subroutine, that makes 2+2n calls. And $_++ won't work. `use strict; use warnings; sub cmap (&) { my $map = shift; return sub { map $map->($_), @_ }; } my $incr = cmap {$_2}; print join " ", $incr->(2..5); print "\n"; # 4 6 8 10` [download] Steffen	[reply] [d/l]

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Re^2: Currying--useful examples?
by tsee (Curate) on Jan 11, 2007 at 08:34 UTC

It's really quite simple to write a curry-able map in Perl. I'd expect it to be pretty slow, though, because of the many subroutine calls: 2+n for a list of n elements. If "map CODE, LIST" treats CODE as a subroutine, that makes 2+2*n calls.
And $_++ won't work.

use strict;
use warnings;

sub cmap (&) {
    my $map = shift;
    return sub { map $map->($_), @_ }; 
}

my $incr = cmap {$_*2};

print join " ", $incr->(2..5);
print "\n";
# 4 6 8 10
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[d/l]