The document outlines common functional functions in Perl, including built-in functions like grep, map, and sort, as well as core and CPAN modules such as List::Util and List::MoreUtils. It provides examples of filtering and transforming lists using these functions, emphasizing the use of simple expressions and code blocks. Additional resources are listed for further exploration of these functions.

1. Perl's Functional Functions

2. The common (core) ones...
● Built-in:
– grep – Filters a list.
– map – Creates or transforms a list.
– sort – Sorts a list.
● List::Util (core)
– first – Like grep, but returns first one found.
– reduce – Summarizes a list.

3. The common CPAN ones:
● List::MoreUtils
– any – Return true if any element in list matches.
– all – Return true if all elements match.
– pairwise – Transform two lists, pairwise, into one.
– Many others!

4. Filtering a list
my @odds;
foreach ( qw( a b c d e ) ) {
push @filtered, $_
if ord( $_ ) % 2;
}
say for @odds;

5. Filtering a list with grep
my @odds;
foreach (
qw( a b c d e )
) {
push @odds, $_
if ord( $_ ) % 2;
}
say for @odds;
my @odds = grep {
ord( $_ ) % 2
} qw( a b c d e );
say for @odds;

6. my @odds = grep { ord($_) % 2 } qw( a b c d e );

7. Which indices contain odd ords?
my @chars = qw( a c f b q r n b d );
my @odds_by_idx = grep {
ord( $chars[$_] ) % 2
} 0 .. $#chars;

8. grep
● list_b = grep { code block } ( list_a )
● Inside code block, $_ is it.
● If code block's return value is true, $_ is appended to
list_b.
● As with foreach, $_ is an alias.
● list_b and list_a need not be arrays.
● Simple expressions may be used in place of code
block.

9. Simple expressions in place of code
block
@explosions = grep { /bkaboomb/i } @phrases;
@explosions = grep /bkaboomb/i, @phrases;
@ones = grep { $_ == 1 } @booleans;
@ones = grep $_ == 1, @booleans;
● If it can't be expressed as a simple expression,
use a code block.
● Expression form requires a comma.

10. Transforming a list
sub chars_to_ords {
my @ords;
foreach ( @_ ) {
push @ords, ord $_;
}
return @ords;
}
my @ord_vals = chars_to_ords( qw( a b c d e ) );

11. Transforming a list with map
sub chars_to_ords {
my @ords;
foreach ( @_ ) {
push @ords, ord $_;
}
return @ords;
}
my @ordinals
= chars_to_ords(
qw( a b c d e )
);
my @ordinals
= map { ord $_ }
qw( a b c d e );

12. my @ordinals = map { ord $_ } qw( a b c d e );

13. Lists don't have to be arrays
say for map { ord } qw( a b c d e );

14. map
● list_b = map { code block } ( list_a )
● Inside code block, $_ is it.
● code block's return value is appended to list_b.
● As with foreach, $_ is an alias.
● list_b and list_a need not be arrays.
● code block is a subroutine; no last, no next.
● Skip current iteration by returning an empty list.

15. Simple expressions don't require
code blocks.
say for map ord, qw( a b c d e );
# The expression form requires a comma.

16. Chaining is legal (even encouraged)
say for
map { $_->[0] }
sort { $a->[1] <=> $b->[1] }
map { [ $_, ord fc $_ ] }
qw( a b c d e );
# The Schwartzian Transform.

17. Sort?
@sorted = sort @unsorted;
@sorted = sort { $a <=> $b } @unsorted; # Ascend, numeric
@sorted = sort { $b <=> $a } @unsorted; # Descend, numeric
@sorted = sort { $a cmp $b } @unsorted; # Ascend, stringy
@sorted = sort {
$a <=> $b || $a cmp $b
} @unsorted; # Ascending numeric, then stringy.
@sorted
= sort { $a->{name} cmp $b->{name} } @unsorted;

18. List::Util
$first_one = first { /^kaboomb/i } @haystack;
$sum = reduce { $a + $b } @numbers;
$max = reduce { $a > $b ? $a : $b } @numbers;

19. List::MoreUtils
$has_quiche = any { /bquicheb/ } @foods; # T/F
$all_unicorns
= all { $_ eq 'unicorn' } @animals; # T/F
@joint_incomes = pairwise { $a + $b } @his, @hers;
@evens_odds = part { $_ % 2 } 1 .. 9; # LOLs

20. List::MoreUtils “natatime”
my @alphabet = ( 'a' .. 'z' );
my $iterator = natatime 3, @alphabet;
while( my @chars = $iterator->() ) {
print “@charsn”;
}
__END__
a b c
d e f
…
y z

21. List::MoreUtils
● Too many to mention them all.
– See https://metacpan.org/module/List::MoreUtils

22. Resources
● perldoc -f grep
● perldoc -f map
● perldoc -f sort
● perldoc List::Util
● https://metacpan.org/module/List::MoreUtils

23. Salt Lake Perl Mongers
http://saltlake.pm.org
Slides on slideshare.net
http://www.slideshare.net/daoswald/perls-functional-functions

24. Dave Oswald
davido@cpan.org