# Raku feature: Lazy list. This construct will repeat 99 to 0
# and then start over at 99 ad infintum when iterated

my @indices = flat (99...0) xx Inf;

# for every index, generate the "xx bottles of beer"
# when using double quotes the Raku parser interprets
# code in curlies as, well, code and embeds the return
# value within the string
# in the first block we see an ordinary logical or
# in the second we see a ternary

my @bottles = @indices.map: -> $n {
    "{$n || 'no more'} bottle{ $n == 1 ?? '' !! 's' } of beer"
};

# generate the first line of each verse
# Raku also has simple string interpolation

my @beers-on-the-wall = @bottles.map: -> $bottles-of-beer {
    "$bottles-of-beer on the wall, $bottles-of-beer\n".tc
};

# Here we see the Z operator at work. It zips together two (or more) lists and returns one value from each.

# generate the second line of each verse
# Note the deconstruction of the incoming sublist into two variables

my @beers-to-get = ( @indices Z @bottles.skip ).map: -> ( $beers-on-the-wall, $beers-available ) {
    "{ $beers-on-the-wall ?? 'Take one down and pass it around' !! 'Go to the store and buy some more' }, $beers-available on the wall.\n"
};

# generate the verses
# Here we are not deconstructing the result of the zip operation, so we get a list we can just join
my @lyrics = ( @beers-on-the-wall Z @beers-to-get).map: -> @parts {
    @parts.join
}

# This is the first time any of the code above actually runs because everything is lazy
# Only when we really ask for values the code runs
# Here we ask for the first 100 values which is one time the whole song
# The ^100 is just a short form to write the range 0..99

.say for @lyrics[ ^100 ];

# Now, here's the kicker. Since the original @indices sequence is infinite we can easily
# display the song twice

.say for @lyrics[ ^200 ];

# Or even forever

.say for @lyrics;