On Wed, Jul 7, 2010 at 02:19, Srinivasa Chaitanya T
<tschaitanya....@gmail.com> wrote:
> Hi,
> How can I write functions which accept block as an argument? Basically I
> want to create a function with like which just executes the block and
> doesn't create an array.
>
> --
> T Srinivasa Chaitanya
>
Unfortunately, in Perl 5 you cannot create a function exactly like map
without resorting to XS trickery; however, you can easily create a
function that takes a function as an argument. All you have to do is
pass a code reference, or coderef for short, to the function. You can
create coderefs in two ways. If you want to create a reference to an
already existing function you say
my $coderef = \&functionname;
If you just want to pass some arbitrary code to a function for it to
run later, a full blown named function is overkill. That is why we
have anonymous subroutines in Perl:
my $coderef = sub { print "hello\n" };
The anonymous sub routine above returns a coderef, but does not
execute the statements between the curly braces. You can call a
coderef by saying
$coderef->("argument1", "arguement2", "etc");
This is the same for coderefs that come from named or anonymous
sources. Bellow I have created a [reduce][1] function in pure Perl
code. You should not use this function as there is a much better XS
based one in [List::Util][2].
You may want to Mark Jason Dominus's book [Higher Order Perl][3] which
is happily also available [on the web][4].
#!/usr/bin/perl
use strict;
use warnings;
sub reduce {
#handle no args or only the function arg
return if @_ < 2;
#handle only the function arg and one data arg
return $_[1] if @_ == 2;
my ($user_defined_function, $first, $second) = @_;
my $accumulator = $user_defined_function->($first, $second);
for my $next (@_[3 .. $#_]) {
$accumulator = $user_defined_function->($accumulator, $next);
}
return $accumulator;
}
sub sum {
return reduce sub { shift() + shift() }, @_;
}
print sum(1, 2, 3, 4), "\n";
[1]: http://en.wikipedia.org/wiki/Reduce_(higher-order_function)
[2]: http://perldoc.perl.org/List/Util.html
[3]: http://www.powells.com/biblio?PID=29575&cgi=product&isbn=1558607013
[4]: http://hop.perl.plover.com/
--
Chas. Owens
wonkden.net
The most important skill a programmer can have is the ability to read.
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