A Higher Order Idea stolen from Ramda.js

Start with Paul Bennett, who is a Perl guy I know from Google Plus. He pointed to a function in Ramda.js, which allows you to create a number of filters as anonymous functions, put them in an array, pass that array, and do that test in one line.

view plainprint?

1. // Instead of   
2.   
3. if ( x > 10 && x % 2 --- 0 ) { console.log( 'Big and Even' ) }  
4.   
5. var gt10 = function(x) { return x > 10 }  
6. var even = R.allPredicates( [ gt10,even ] ) ;  
7.   
8. if ( f( x ) ) { console.log( 'Big and Even' ) }  

// Instead of 

if ( x > 10 && x % 2 --- 0 ) { console.log( 'Big and Even' ) }

var gt10 = function(x) { return x > 10 }
var even = R.allPredicates( [ gt10,even ] ) ;

if ( f( x ) ) { console.log( 'Big and Even' ) }

Now, imagine if we're testing several things, rather than just one.

I thought "Hey, there's so much I could do with this in Perl. I've been thinking about writing a mail filter that takes a function Higher Order Perl style, so could generate a function based on the config file and pass it into the middle of Mail::IMAPClient so I don't have to generate a menagerie of one-trick ponies. This, of course, is a fairly big idea to work with, and the allPredicates is small enough that, with a half-hour of working through Perl I mostly thought I knew, I came up with this. Fifteen lines of code. I am happy.

	#!/usr/bin/env perl
	use feature qw'say state' ;
	use strict ;
	use utf8 ;
	use warnings ;
	use Data::Dumper ;
	# https://plus.google.com/u/0/+PaulBennett/posts/EvLLxiAMjKR
	# http://ramdajs.com/docs/R.html
	# SAMPLE CODE
	# var gt10 = function(x) { return x > 10; };
	# var even = function(x) { return x % 2 === 0};
	# var f = R.allPredicates([gt10, even]);
	# f(11); //=> false
	# f(12); //=> true
	my $gt10 = sub { my $i = shift ; return $i > 10 } ;
	my $even = sub { my $i = shift ; return $i % 2 == 0 } ;
	my $odd = sub { my $i = shift ; return $i % 2 == 1 } ;
	my $test = sub { say Dumper \@_ } ;
	# my $f = allPredicates( $test ) ;
	my $f = allPredicates( $gt10 , $even ) ;
	my $g = allPredicates( $gt10 , $odd ) ;
	for my $i ( 9 .. 20 ) {
	if ( &$f( $i ) ) { say $i . ' big and even' }
	}
	for my $i ( map { $_ * 3 } 1 .. 10 ) {
	if ( &$g( $i ) ) { say $i . ' big and odd' }
	}
	# say &$gt10( 1 );
	# say &$gt10( 12 );
	# say &$even( 1 );
	# say &$even( 12 );
	# say &$odd( 1 );
	# say &$odd( 12 );
	sub allPredicates {
	my @functions = @_ ;
	my $function = sub {
	my $val = shift ;
	my @tests = @functions ;
	my @results ;
	for my $t ( @tests ) {
	my $r = &$t( $val ) ;
	push @results, $r if $r ;
	}
	return 1 if scalar @tests == scalar @results ;
	return 0 ;
	} ;
	return $function ;
	}

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