Re^2: Why Perl Is Not My Favourite Functional Programming Language

[FoxtrotUniform]

in reply to Re: Why Perl Is Not My Favourite Functional Programming Language
in thread A mini-language for sequences (part 1)

Have you tried prototypes?

Briefly. I don't fully grok the try/catch example in perldoc perlsub, so I may be missing something, but my failed attempts look like:

#! /usr/bin/perl

use strict;
use warnings;

sub curry(&@)
{
    my ($fn, @args) = @_;

    return sub {
        $fn->(@args, @_);
    }
}

&curry(+, 2)->();

which of course does not compile. (There's also the issue that in order to really do higher-order functions with prototypes, I'd need to somehow examine fn's prototype and preserve it in the returned sub.)

I'm thinking that a source filter might help, turning builtins used as values into anonymous subs, but I don't know very much about source filters — I'm not even sure that they do what I think they do.

[itub]

Perhaps I misunderstood what you wanted. While you are certainly in trouble if you want to curry the + operator, I see no problem with a function such as sum.

use strict;
use warnings;
use List::Util qw(sum);

sub curry(&@)
{
    my ($fn, @args) = @_;
    return sub {
        $fn->(@args, @_);
    }
}

my $f = curry { sum(@_) } 5;

print $f->(3); # prints 8 (5 + 3)

[brian_d_foy]

Check out the functions in Object::Iterate, where I define the imap and igrep functions. I discuss this in my Iterator Design Pattern article for The Perl Review 0.5 (September 2002).

The next issue of The Perl Review will include "Functional Programming in Perl" which discusses higher order functions in Perl.