Applying an array to a function

eklerks has asked for the wisdom of the Perl Monks concerning the following question:

Dear Monks,

I have created an entity, which applies the elements to another entity, but the incantation follows the path of the black arts. I have to call upon another Perl Daemon to grant it life. Please show me my wrongs.

For the less spiritual enlighted:
It is a function, which applies the elements of an array to another function. Like the javascript apply. Here it is:

sub repeat {
        my $n = shift;
        my $x = shift;
        my $array = [];
        for($i = 0; $i < $n; $i++){
                push @{$array}, $x;
        }
        return $array;
}


sub apply {
        my ($func, $args) = @_;
        my $size = @{$args};
        my $app = repeat($size, '(shift @{$x})');
        eval 'sub _apply { my $f = shift; my $x = shift; $f->(' . join
+(',', @{$app}) . '); }';
        return _apply(\&$func, $args);
}
[download]

It does its job, but I have understood, that when I call eval another perl interpreter will be started. This is of course not very efficient. Is there a better way to get around this?

I thought about generating a couple of static functions like apply1 apply2 apply3 etc and put it in a package. But I find this offending too.

Example:

sub test {
        my $x = shift;
        my $y = shift;
        my $z = shift;
        print $x + $y + $z;
}
# output 6
apply(\&test, [1,2,3]);
[download]

Thanks for your help!

Comment on Applying an array to a function Select or Download Code

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Re: Applying an array to a function by BrowserUk (Patriarch) on May 29, 2010 at 23:21 UTC
This does the same thing? `#! perl -slw use strict; sub test { my $x = shift; my $y = shift; my $z = shift; print $x + $y + $z; } sub apply2 { my( $code, $argsRef ) = @_; return $code->( @$argsRef ); } apply2( \&test, [1,2,3] );` [download]	[reply] [d/l]
Re^2: Applying an array to a function by eklerks (Novice) on Jun 02, 2010 at 14:02 UTC
Ah yes, I was searching for something like that. I knew I didn't need the eval to achieve my goals. Eval is Evil. Most of the times. If I had took some time, I would have realised, that (pseudocode): `@t = (1,2,3); test(@t) == test((1,2,3)) == test(1,2,3);` [download] So the apply function isn't needed either, I can just write (like your example): `test(@{[1,2,3]});` [download] Thanks	[reply] [d/l] [select]
Re: Applying an array to a function by choroba (Cardinal) on May 29, 2010 at 23:35 UTC
What BrowserUk said is what I think as well. You do not need the `repeat` sub, and if you do for something else, you can shorten it like this: `sub repeat { my ($n,$x) = @_; my $array = []; @{$array} = ($x) x $n; return $array; }` [download]	[reply] [d/l] [select]
Re^2: Applying an array to a function by ikegami (Patriarch) on May 31, 2010 at 03:19 UTC
Since you were trying to simplify the code, it should be noted that `my $array = []; @{$array} = ($x) x $n; return $array;` [download] is a complicated way of writing `my @array = ($x) x $n; return \@array;` [download] or `my $array = [ ($x) x $n ]; return $array;` [download] or `return [ ($x) x $n ];` [download]	[reply] [d/l] [select]
Re^3: Applying an array to a function by eklerks (Novice) on Jun 02, 2010 at 14:10 UTC
I use haskell a lot lately and it is nice to see that your last version is very close to how you can implement repeat into haskell: `repeat a = [a,a..]` [download] Perl can be a really concise language. It astonish me time after time. I am really looking forward to perl6. (In haskell it is an infinite list, how is this in perl6?) I got the answer already. Perl6 is also lazy evaluated, so infinite lists are supported.	[reply] [d/l]