#!/usr/bin/pugs

use v6-alpha;

#P01 (*) Find the last box of a list.
#    Example:
#    * (my-last '(a b c d))
#    (D)

<a b c d>[-1].say;

#P02 (*) Find the last but one box of a list.
#    Example:
#    * (my-but-last '(a b c d))
#    (C D)

<a b c d>[-2, -1].perl.say;

#P03 (*) Find the K'th element of a list.
#    The first element in the list is number 1.
#    Example:
#    * (element-at '(a b c d e) 3)
#    C

<a b c d>[2].perl.say;

#P04 (*) Find the number of elements of a list.

<a b c d>.elems.say;

#P05 (*) Reverse a list.

<a b c d>.reverse.perl.say;

#P06 (*) Find out whether a list is a palindrome.
#    A palindrome can be read forward or backward; e.g. (x a m a x).

for [<a b c b a>], [<a b c b c a>] -> $array {
    if $array.reverse ~~ $array {
        say $array.perl ~ " is a palindrome";
    }
    else {
        say $array.perl ~ " is not a palindrome";
    }
}

#P07 (**) Flatten a nested list structure.
#    Transform a list, possibly holding lists as elements into a `flat' list by
#    replacing each list with its elements (recursively).


# courtesy of Wim Vanderbauwhede from the perl6-users list
my $flatten = -> $x { $x.isa(Array) ?? ( map $flatten, $x ) !! $x }; 
my @flattened = map $flatten, ('a', ['b', ['c', 'd', 'e']]);
@flattened.perl.say;

#P08 (**) Eliminate consecutive duplicates of list elements.
#    If a list contains repeated elements they should be replaced with a single
#    copy of the element. The order of the elements should not be changed.

#    Example:
#    * (compress '(a a a a b c c a a d e e e e))
#    (a b c a d E)

my $compress = do {
    my $previous;
    $compress = sub ($x) {
        if $x ne $previous {
            $previous = $x;
            return $x;
        }
        else {
            return;
        }
    };
}
my @compressed = map $compress, <a a a a b c c a a d e e e e>;
@compressed.perl.say;

#P09 (**) Pack consecutive duplicates of list elements into sublists.
#    If a list contains repeated elements they should be placed in separate sublists.
#
#    Example:
#    * (pack '(a a a a b c c a a d e e e e))
#    ((A A A A) (B) (C C) (A A) (D) (E E E E))

my @packed;
{
    my @sublist;
    my $previous;
    for <a a a a b c c a a d e e e e> -> $x {
        if $x eq $previous {
            @sublist.push($x);
            next;
        }
        $previous = $x;
        if @sublist {
            @packed.push([@sublist]);
            @sublist = $x;
        }
    }
    @packed.push([@sublist]);
}
@packed.perl.say;