Subroutine chaining idiom requested

There was a near article in about Issue 19 of the Perl Journal called "Design Patterns" in which this guy had a neat one-liner. Let's say we have;

$agenda = [ \a, \b, \c ];

where a, b, c are subs which expect and return arrays.

He wrote a one-liner which ran through the subs, taking the output of one and sending it in as the input of the next sub.

[merlyn]

use List::Util qw(reduce); # unnecessary in in Perl 6 {grin}
my @result = reduce { [$b->{@$a}] } [], @$agenda;

Or, without that:

my @result;
@result = $_->(@result) for @$agenda;

-- Randal L. Schwartz, Perl hacker

[premchai21]

Hmmm... I've never read that, but to just construct one on my own:

$agenda = [ sub { "Hello" }, sub { scalar reverse shift }, sub { chop 
+shift } ];
chain($agenda, [ ]);

### BEGIN GOLF MODE ###
sub chain($$) { my@x=@{+pop};foreach(@{+shift}){@x=$_->(@x)}@x }
### END GOLF MODE ###

Update: Fixed argument-modification error, thanks to tilly for pointing that out.

[tilly]

Did someone say golf?

sub chain{(*f,*_)=@_;@_=&$_ for@f;@_}

Of course you probably want strict compliant and it is bad style to modify your arguments in place. In which case it is probably better to make that:

sub chain{my($f,$a)=@_;$a=[&$_(@$a)]for@$f;@$a}

which is still reasonable...

[tachyon]

Here's mine, 34 chars for the task which did not specify a print requirement. 32 without the my for strict compliance. 27 if you use something shorter than $agenda like $a

tachyon

use strict;

# a ref to a few subrefs to go, performing as secified
# in that they take an array, do someting and return an array
my $agenda = [
            sub{my@in=@_;for(@in){$_=$_*2}@in;},
            sub{my@in=@_;for(@in){$_=$_*2}@in;},
            sub{my@in=@_;for(@in){$_=$_*2}@in;},
];

# four
my@a=(1,2,3);@a=&$_(@a)for@$agenda;print"@a";

Edited 2001-05-24 by Ovid

[tachyon]

A few more variations on the theme

tachyon

use strict;

# a few subrefs to go, performing as specified
my $agenda = [
            sub{my@in=@_;for(@in){$_=$_*2}@in;},
            sub{my@in=@_;for(@in){$_=$_*2}@in;},
            sub{my@in=@_;for(@in){$_=$_*2}@in;},
];

# here is a little sub of 39 chars

print chain(1,2,3,$agenda);

sub chain{
    my$a=pop;
    @_=&$_(@_)for@$a;
    @_
}

# here it is as an anonymous sub
print&{sub{my$a=pop;@_=&$_(@_)for@$a;@_}}(1,2,3,$agenda);

[FouRPlaY]

Is it just me, or is everything on this site turning into a golf challenge? =)



FouRPlaY
Learning Perl or Going To die() Trying

[Ovid]

FouRPlaY wrote:

Is it just me, or is everything on this site turning into a golf challenge? =)

78 letters. My solution:

Imagining? Does all here become golf?

37 letters. Though with English, one might argue that I've altered the meaning.

Cheers,
Ovid

Join the Perlmonks Setiathome Group or just click on the the link and check out our stats.

[tilly]

35 characters. :-)

Imagining? Turns all here to golf?

And restucturing produces the 29 character logical equivalent of:

All here to golf or me only.

I don't think that can be improved much. :-)

[Anonymous Monk]

28 chars and parses under strict

use strict;
'I',? you.Is all here->GOLF?

tachyon