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Re: Currying--useful examples?

by Errto (Vicar)
on Jan 11, 2007 at 00:56 UTC ( #594040=note: print w/ replies, xml ) Need Help??


in reply to 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);
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 }; }
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+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

    Steffen

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