class List

Sequence of values

my class List is Iterable does Positional { }

List stores items sequentially and potentially lazily.

Indexes into lists and arrays start at 0 by default.

You can assign to list elements if they are containers. Use Arrays to have every value of the list stored in a container.

Items, Flattening and Sigils

In Perl 6, assigning a List to a scalar variable does not lose information. The difference is that iteration generally treats a list (or any other list-like object, like a Seq or an Array) inside a scalar as a single element, as long as it's part of another .

my @a = 1, 2, 3;
for @a { }      # three iterations

my $s = @a;
for $s { }      # one iteration
for @a.item { } # one iteration
for $s.list { } # three iterations

Lists generally don't interpolate (flatten) into other lists, except when they are not itemized, and the single argument to an operation such as append:

my @a = 1, 2, 3;
my @nested = @a, @a;           # two elements
my @flat = flat @a, @a;        # six elements, with explicit flat
my @b = 'a', 'b';
@b.append: @a;                 # @b now has 5 elements, because @a
                               # is the sole argument to append
my @c = 'a', 'b';
@c.append: $@a;                # @b now has 3 elements, because of the
                               # itemization with $
say @c.elems;

.item can often be written as $( ... ), and on an array variable even as $@a.

The same flattening behavior applies all objects that do the Iterable role, notable hashes:

my %h = a => 1, b => 2;
my @b = %h;   say @b.elems;     # 2
my @c = %h, ; say @c.elems;     # 1
my @d = $%h;  say @d.elems;     # 1

Slurpy parameters (*@a) flatten non-itemized sublists:

sub fe(*@flat) { @flat.elems }
say fe(<a b>, <d e>);           # 4
say fe(<a b>, <d e>.item);      # 3

Methods

routine elems

Defined as:

multi sub    elems($list)  returns Int:D
multi method elems(List:D:) returns Int:D

Returns the number of elements in the list.

say (1,2,3,4).elems; # 4

routine end

Defined as:

multi sub    end($list)  returns Int:D
multi method end(List:D:) returns Int:D

Returns the index of the last element.

say (1,2,3,4).end; # 3

routine keys

Defined as:

multi sub    keys($list)  returns Seq:D
multi method keys(List:D:) returns Seq:D

Returns a sequence of indexes into the list (e.g., 0..(@list.elems-1)).

say (1,2,3,4).keys; # 0..3

routine values

Defined as:

multi sub    values($list)  returns Seq:D
multi method values(List:D:) returns Seq:D

Returns a sequence of the list elements, in order.

say (1,2,3,4).WHAT;        # (List)
say (1,2,3,4).values.WHAT; # (Seq)

routine kv

Defined as:

multi sub    kv($list)  returns Seq:D
multi method kv(List:D:) returns Seq:D

Returns an interleaved sequence of indexes and values. For example

<a b c>.kv; # (0 a 1 b 2 c)

routine pairs

Defined as:

multi sub    pairs($list)   returns Seq:D
multi method pairs(List:D:) returns Seq:D

Returns a sequence of pairs, with the indexes as keys and the list values as values.

<a b c>.pairs   # (0 => a 1 => b 2 => c)

routine antipairs

Defined as:

multi method antipairs(List:D:) returns Seq:D

Returns a Seq of pairs, with the values as keys and the indexes as values, i.e. the direct opposite to pairs.

say <a b c>.antipairs;  # (a => 0 b => 1 c => 2)

routine join

Defined as:

multi sub    join($separator, *@list) returns Str:D
multi method join(List:D: $separator) returns Str:D

Treats the elements of the list as strings, interleaves them with $separator and concatenates everything into a single string.

Example:

join ', ', <a b c>;             # a, b, c

Note that the method form does not flatten sublists:

say (1, <a b c>).join('|');     # 1|a b c

routine map

Defined as:

multi sub    map(&code, *@elems) returns Seq:D
multi method map(List:D: &code) returns Seq:D

Invokes &code for each element and gathers the return values in a sequence and returns it. This happens lazily, i.e. &code is only invoked when the return values are accessed.

Examples:

say ('hello', 1, 22/7, 42, 'world').map: { .WHAT.perl } # (Str Int Rat Int Str)
say map *.Str.chars, 'hello', 1, 22/7, 42, 'world';     # (5 1 8 2 5)

map inspects the arity of the code object, and tries to pass as many arguments to it as expected:

sub b($a, $b) { "$a before $b" };
say <a b x y>.map(&b).join(', ');   # a before b, x before y

iterates the list two items at a time.

Note that map does not flatten embedded lists and arrays, so

((1, 2), <a b>).map({ .join(',')})

passes (1, 2) and <a b> in turn to the block, leading to a total of two iterations and the result sequence "1,2", "a,b". See method flatmap for an alternative that flattens.

sub flat

Defined as:

sub flat(**@list is raw)

Constructs a list which contains any arguments provided in the order provided, and returns the result of calling the .flat method (inherited from Any) on that list:

say flat 1, (2, (3, 4), $(5, 6)); # (1 2 3 4 (5 6))

method flatmap

Defined as:

method flatmap(List:D: &code) returns Seq:D

Like map iterates over the elements of the invocant list, feeding each element in turn to the code reference, and assembling the return values from these invocations in a result list.

Unlike map it flattens non-itemized lists and arrays, so

say ((1, 2), <a b>).flatmap(&uc).join('|');     # 1 2|A B

invokes uc four times.

routine grep

Defined as:

multi sub    grep(Mu $matcher, *@elems, :$k, :$kv, :$p, :$v) returns Seq:D
multi method grep(List:D:  Mu $matcher, :$k, :$kv, :$p, :$v) returns Seq:D

Returns a sequence of elements against which $matcher smart-matches. The elements are returned in the order in which they appear in the original list.

Examples:

say ('hello', 1, 22/7, 42, 'world').grep: Int;              # (1 42)
say grep { .Str.chars > 3 }, 'hello', 1, 22/7, 42, 'world'; # (hello 3.142857 world)

The optional named parameters :k, :kv, :p, :v provide the same functionality as on slices:

Only return the index values of the matching elements in order.

Return both the index and matched elements in order.

Return the index and the matched element as a Pair, in order.

Only return the matched elements (same as not specifying any named parameter at all).

Examples:

say ('hello', 1, 22/7, 42, 'world').grep: Int, :k; # (1 3)
say grep { .Str.chars > 3 }, :kv, 'hello', 1, 22/7, 42, 'world'; # (0 hello 2 3.142857 4 world)
say grep { .Str.chars > 3 }, :p, 'hello', 1, 22/7, 42, 'world'; # (0 => hello 2 => 3.142857 4 => world)

routine first

Defined as:

multi sub    first(Mu $matcher, *@elems, :$k, :$kv, :$p, :$end)
multi method first(List:D:  Mu $matcher, :$k, :$kv, :$p, :$end)

Returns the first item of the list which smart-matches against $matcher, returns Nil when no values match. The optional named parameter :end indicates that the search should be from the end of the list, rather than from the start.

Examples:

say (1, 22/7, 42, 300).first: * > 5;                  # 42
say (1, 22/7, 42, 300).first: * > 5, :end;            # 300
say ('hello', 1, 22/7, 42, 'world').first: Complex;   # Nil

The optional named parameters :k, :kv, :p provide the same functionality as on slices:

Return the index value of the matching element. Index is always counted from the beginning of the list, regardless of whether the :end named parameter is specified or not.

Return both the index and matched element.

Return the index and the matched element as a Pair.

Examples:

say (1, 22/7, 42, 300).first: * > 5, :k;        # 2
say (1, 22/7, 42, 300).first: * > 5, :p;        # 2 => 42
say (1, 22/7, 42, 300).first: * > 5, :kv, :end; # (3 300)

method head

Defined as:

multi method head(List:D: Int(Cool) $number = 1) returns Seq:D

Returns the first NUMBER items of the list. Returns an empty list if NUMBER <= 0. Defaults to the first element seen if no NUMBER specified.

Examples:

say ^10 .head(5);      # (0 1 2 3 4)
say ^Inf .head(5);     # (0 1 2 3 4)
say ^10 .head;         # (0)
say ^Inf .head;         # (0)

method tail

Defined as:

multi method tail(List:D: Int(Cool) $number = 1) returns Seq:D

Returns a Seq containing the last NUMBER items of the list. Returns an empty Seq if NUMBER <= 0. Defaults to the last element if no NUMBER is specified. Throws an exception if the list is lazy.

Examples:

say ^10 .tail(5)      # (5 6 7 8 9)
say ^Inf .tail(5)     # Cannot tail a lazy list
say ^10 .tail         # (9)
say ^Inf .tail        # Cannot tail a lazy list

routine categorize

Defined as:

multi sub    categorize(&mapper, *@values) returns Hash:D
multi method categorize(List:D: &mapper)   returns Hash:D

Transforms a list of values into a hash representing the categorizations of those values according to a mapper; each hash key represents one possible categorization for one or more of the incoming list values, and the corresponding hash value contains an array of those list values categorized by the mapper into the category of the associated key.

Note that, unlike classify, which assumes that the return value of the mapper is a single value, categorize always assumes that the return value of the mapper is a list of categories that are appropriate to the current value.

Example:

sub mapper(Int $i) returns List {
    $i %% 2 ?? 'even' !! 'odd',
    $i.is-prime ?? 'prime' !! 'not prime'
}
say categorize &mapper, (1, 7, 6, 3, 2);   # {even => [6 2], not prime => [1 6],
                                           #  odd => [1 7 3], prime => [7 3 2]}

routine classify

Defined as:

multi sub    classify(&mapper, *@values) returns Hash:D
multi method classify(List:D: &mapper)   returns Hash:D

Transforms a list of values into a hash representing the classification of those values according to a mapper; each hash key represents the classification for one or more of the incoming list values, and the corresponding hash value contains an array of those list values classified by the mapper into the category of the associated key.

Example:

say classify { $_ %% 2 ?? 'even' !! 'odd' }, (1, 7, 6, 3, 2);
    # {even => [6 2], odd => [1 7 3]}
say ('hello', 1, 22/7, 42, 'world').classify: { .Str.chars };
    # {1 => [1], 2 => [42], 5 => [hello world], 8 => [3.142857]}

method Bool

Defined as:

multi method Bool(List:D:) returns Bool:D

Returns True if the list has at least one element, and False for the empty list.

say ().Bool;  # False
say (1).Bool; # True

method Str

Defined as:

multi method Str(List:D:) returns Str:D

Stringifies the elements of the list and joins them with spaces (same as .join(' ')).

say (1,2,3,4,5).Str; # 1 2 3 4 5

method Int

Defined as:

multi method Int(List:D:) returns Int:D

Returns the number of elements in the list (same as .elems).

say (1,2,3,4,5).Int; # 5

method Numeric

Defined as:

multi method Numeric(List:D:) returns Int:D

Returns the number of elements in the list (same as .elems).

say (1,2,3,4,5).Numeric; # 5

method Capture

Defined as:

method Capture() returns Capture:D

Returns a Capture where each Pair, if any, in the List has been converted to a named argument. All other elements in the List are converted to positional arguments in the order they are found, i.e. the first non pair item in the list becomes the first positional argument, which gets index 0, the second non pair item becomes the second positional argument, getting index 1 etc.

my $list = (7, 5, a => 2, b => 17);
my $capture = $list.Capture;
say $capture.keys;                                # (0 1 a b)
my-sub(|$capture);                                # 7, 5, 2, 17

sub my-sub($first, $second, :$a, :$b) {
    say "$first, $second, $a, $b"
}

A more advanced example demonstrating the returned Capture being matched against a Signature.

my $list = (7, 5, a => 2, b => 17);
say so $list.Capture ~~ :($ where * == 7,$,:$a,:$b); # True

$list = (8, 5, a => 2, b => 17);
say so $list.Capture ~~ :($ where * == 7,$,:$a,:$b); # False

routine pick

Defined as:

multi sub    pick($count, *@list) returns Seq:D
multi method pick(List:D: $count = 1) returns Mu

Returns $count elements chosen at random and without repetition from the invocant. If * is passed as $count, or $count is greater than or equal to the size of the list, then all elements from the invocant list are returned in a random sequence.

Examples:

say <a b c d e>.pick;           # b
say <a b c d e>.pick: 3;        # (c a e)
say  <a b c d e>.pick: *;       # (e d a b c)

routine roll

Defined as:

multi sub    roll($count, *@list) returns Seq:D
multi method roll(List:D: $count = 1)

Returns a sequence of $count elements, each randomly selected from the list. Each random choice is made independently, like a separate die roll where each die face is a list element.

If * is passed to $count, returns a lazy, infinite sequence of randomly chosen elements from the original list.

Examples:

say <a b c d e>.roll;       # b
say <a b c d e>.roll: 3;    # c c e
say roll 8, <a b c d e>;    # b a e d a e b c

my $random_digits := (^10).roll(*);
say $random_digits[^15];    # 3 8 7 6 0 1 3 2 0 8 8 5 8 0 5

routine eager

Defined as:

multi method eager(List:D:) returns List:D
sub eager(*@elems) returns List:D

Evaluates all elements in the list eagerly, and returns them as a list.

say (1,2,3,4,5).eager; # 1 2 3 4 5

routine reverse

Defined as:

multi sub    reverse(*@list ) returns List:D
multi method reverse(List:D:) returns List:D

Returns a list with the same elements in reverse order.

Note that reverse always refers to reversing elements of a list; to reverse the characters in a string, use flip.

Examples:

say <hello world!>.reverse;     # (world! hello)
say reverse ^10;                # (9 8 7 6 5 4 3 2 1 0)

routine rotate

Defined as:

multi sub    rotate(@list,  Int:D $n = 1) returns List:D
multi method rotate(List:D: Int:D $n = 1) returns List:D

Returns the list rotated by $n elements.

Examples:

<a b c d e>.rotate(2);   # <c d e a b>
<a b c d e>.rotate(-1);  # <e a b c d>

routine sort

Defined as:

multi sub    sort(*@elems)      returns Seq:D
multi sub    sort(&by, *@elems) returns Seq:D
multi method sort(List:D:)      returns Seq:D
multi method sort(List:D: &by) returns Seq:D

Sorts the list, smallest element first. By default infix:<cmp> is used for comparing list elements.

If &by is provided, and it accepts two arguments, it is invoked for pairs of list elements, and should return Order::Increase, Order::Same or Order::Decrease.

If &by accepts only one argument, the list elements are sorted according to by($a) cmp by($b) . The return values of &by are cached, so that &by is only called once per list element.

Examples:

say (3, -4, 7, -1, 2, 0).sort;                  # (-4 -1 0 2 3 7)
say (3, -4, 7, -1, 2, 0).sort: *.abs;           # (0 -1 2 3 -4 7)
say (3, -4, 7, -1, 2, 0).sort: { $^b leg $^a }; # (7 3 2 0 -4 -1)

routine unique

Defined as:

multi sub    unique(*@values, :&as, :&with) returns Seq:D
multi method unique(List:D:  :&as, :&with) returns Seq:D

Returns a sequence of unique values from the invocant/argument list, such that only the first occurrence of each duplicated value remains in the result list. unique uses the semantics of the === operator to decide whether two objects are the same, unless the optional :with parameter is specified with another comparator. The order of the original list is preserved even as duplicates are removed.

Examples:

say <a a b b b c c>.unique;   # (a b c)
say <a b b c c b a>.unique;   # (a b c)

(Use squish instead if you know the input is sorted such that identical objects are adjacent.)

The optional :as parameter allows you to normalize/canonicalize the elements before unique-ing. The values are transformed for the purposes of comparison, but it's still the original values that make it to the result list:

Example:

say <a A B b c b C>.unique(:as(&lc))          # (a B c)

One can also specify the comparator with the optional :with parameter. For instance if one wants a list of unique hashes, one could use the eqv comparator.

Example:

my @list = {a => 42}, {b => 13}, {a => 42};
say @list.unique(:with(&[eqv]))               # ({a => 42} {b => 13})

routine repeated

Defined as:

multi sub    repeated(*@values, :&as, :&with) returns Seq:D
multi method repeated(List:D:  :&as, :&with) returns Seq:D

Returns a sequence of repeated values from the invocant/argument list. It takes the same parameters as unique, but instead of passing through any elements when they're first seen, they're only passed through as soon as they're seen for the second time (or more).

Examples:

say <a a b b b c c>.repeated;                   # (a b b c)
say <a b b c c b a>.repeated;                   # (b c b a)
say <a A B b c b C>.repeated(:as(&lc));         # (A b b C)

my @list = {a => 42}, {b => 13}, {a => 42};
say @list.repeated(:with(&[eqv]))               # ({a => 42})

routine squish

Defined as:

multi sub    squish(*@values, :&as) returns Seq:D
multi method squish(List:D:  :&as) returns Seq:D

Returns a sequence of values from the invocant/argument list where runs of more than one value are replaced with only the first instance. Like unique, squish uses the semantics of the === operator to decide whether two objects are the same. Unlike unique, this function only removes adjacent duplicates; identical values further apart are still kept. The order of the original list is preserved even as duplicates are removed.

Examples:

say <a a b b b c c>.squish; # (a b c)
say <a b b c c b a>.squish; # (a b c b a)

The optional :as parameter, just like with unique, allows values to be temporarily transformed before comparison.

routine reduce

Defined as:

multi sub    reduce(&with, *@values)
multi method reduce(List:D: &with)

Generates a single "combined" value from a list of arbitrarily many of values, by iteratively applying a function which knows how to combine two values.

If @values contains just a single element, that element is returned immediately. If it contains no elements, an exception is thrown, unless &with is an operator with a known identity value. For this reason, you may want to prefix the input list with an explicit identity value:

my @strings = ("One good string!", "And one another good string!");
say reduce { $^a ~ $^b }, '', |@strings;               # like @strings.join
my @numbers = (1,2,3,4,5);
say reduce { $^a > $^b ?? $^a !! $^b }, 0, |@numbers;  # like @numbers.max

If &with is the function object of an operator, its inherent identity value and associativity is respected - in other words, (VAL1, VAL2, VAL3).reduce(&[OP]) is the same as VAL1 OP VAL2 OP VAL3 even for operators which aren't left-associative:

# Raise 2 to the 81st power, because 3 to the 4th power is 81
[2,3,4].reduce(&[**]).lsb.say;        # 81
(2**(3**4)).lsb.say;                  # 81
(2**3**4).lsb.say;                    # 81

# Subtract 4 from -1, because 2 minus 3 is -1
[2,3,4].reduce(&[-]).say;             # -5
((2-3)-4).say;                        # -5
(2-3-4).say;                          # -5

Since reducing with an infix operator is a common thing to do, the [ ] meta-operator provides a syntactic shortcut:

# The following all do the same thing...
my @numbers = (1,2,3,4,5);
say reduce { $^a + $^b }, 0, |@numbers;
say reduce * + *, 0, |@numbers;
say reduce &[+], @numbers; # operator does not need explicit identity
say [+] @numbers;          # most people write it this way

Since reduce is an implicit loop, it responds to next, last and redo statements inside &with:

say (2,3,4,5).reduce: { last if $^a > 7; $a + $^b }; # says 9

Practical example:

# Generate a random-ish math formula like "(4 + ((3 * x) + 11) / 6))"

my @ops = [Z] (<+ - * />, 1..20)».roll(4);

say ('x', |@ops).reduce: -> $formula, [$op, $number] {
    Bool.pick ?? "($formula $op $number)"
              !! "($number $op $formula)"
}

Note: In the functional programming world, this operation is generally called a fold. With a right-associative operator it is a right fold, otherwise (and usually) it is a left fold.

routine combinations

Defined as:

multi sub    combinations($n, $k)                     returns Seq:D
multi method combinations(List:D: Int:D $of)          returns Seq:D
multi method combinations(List:D: Range:D $of = 0..*) returns Seq:D

The Int variant returns all $of-combinations of the invocant list. For example

say .join('|') for <a b c>.combinations(2);
# a|b
# a|c
# b|c

because all the 2-combinations of 'a', 'b', 'c' are ['a', 'b'], ['a', 'c'], ['b', 'c'].

The Range variant combines all the individual combinations into a single list, so

say .join('|') for <a b c>.combinations(2..3);
# a|b
# a|c
# b|c
# a|b|c

because that's the list of all 2- and 3-combinations.

The subroutine form combinations($n, $k) is equivalent to (^$n).combinations($k), so

.say for combinations(4, 2)
# 0 1
# 0 2
# 0 3
# 1 2
# 1 3
# 2 3

routine permutations

Defined as:

multi sub    permutations($n)      returns Seq:D
multi method permutations(List:D:) returns Seq:D

Returns all possible permutations of a list as a sequence of lists. So

say .join('|') for <a b c>.permutations
# a|b|c
# a|c|b
# b|a|c
# b|c|a
# c|a|b
# c|b|a

permutations treats all list elements as distinguishable, so (1, 1, 2).permutations still returns a list of 6 elements, even though there are only three distinct permutations.

The subroutine form permutations($n) is equivalent to (^$n).permutations, so

.say for permutations 3;
# 0 1 2
# 0 2 1
# 1 0 2
# 1 2 0
# 2 0 1
# 2 1 0

method rotor

Defined as:

method rotor(*@cycle, Bool() :$partial) returns Seq:D

Returns a sequence of lists, where each sublist is made up of elements of the invocant.

In the simplest case, @cycle contains just one integer, in which case the invocant list is split into sublists with as many elements as the integer specifies. If :$partial is True, the final chunk is included even if it doesn't satisfy the length requirement:

say ('a'..'h').rotor(3).join('|');              # a b c|d e f
say ('a'..'h').rotor(3, :partial).join('|');    # a b c|d e f|g h

If the element of @cycle is a Pair instead, the key of the pair specifies the length of the return sublist, and the value the gap between sublists; negative gaps produce overlap:

say ('a'..'h').rotor(2 => 1).join('|');         # a b|d e|g h
say ('a'..'h').rotor(3 => -1).join('|');        # a b c|c d e|e f g

If @cycle contains more than element, rotor cycles through it to find the number of elements for each sublist:

say ('a'..'h').rotor(2, 3).join('|');           # a b|c d e|f g
say ('a'..'h').rotor(1 => 1, 3).join('|');      # a|c d e|f

Combining multiple cycles and :partial also works:

say ('a'..'h').rotor(1 => 1, 3 => -1, :partial).join('|');
                                                # a|c d e|e|g h

See this blog post for more elaboration on rotor.

routine zip

Defined as:

sub zip(**@e) returns Seq:D

Zips two or more lists or other iterables together by returning a sequence made of a list of all first elements of all lists, then a list of all second elements of a list etc.

say .join for zip  <a b c>, <d e f>;
# ad
# be
# cf

zip has an infix synonym, the Z operator.

say .join for <a b c> Z <d e f>;    # same output as above

When the first input list is exhausted, no more elements are returned; so trailing elements from longer input lists are discarded.

If you just wish to skip missing entries in shorter sublists, use roundrobin instead:

for roundrobin(@queue1, @queue2, @queue3) -> $next {
    ...
}

sub roundrobin

Defined as:

method roundrobin(List:D:) returns Seq

roundrobin is very similar to zip. The difference is that roundrobin will not stop on lists that run out of elements but simply skip any undefined value:

my @a = 1;
my @b = 1..2;
my @c = 1..3;
for flat roundrobin(@a, @b, @c) -> $x { $x.say }

will display the following values: 1, 1, 1, 2, 2, 3

routine sum

Defined as:

multi sub    sum($list)  returns Numeric:D
multi method sum(List:D:) returns Numeric:D

Returns the sum of all elements in the list or 0 if the list is empty. Throws an exception if an element can not be coerced into Numeric.

say (1, 3, pi).sum;       # 7.14159265358979
say (1, "0xff").sum;      # 256
say sum(0b1111, 5);       # 20

method fmt

Defined as:

method fmt($format = '%s', $separator = ' ') returns Str:D

Returns a string where each element in the list has been formatted according to $format and where each element is separated by $separator.

For more information about formats strings, see sprintf.

my @a = 8..11;
say @a.fmt('%03d', ',');                          # 008,009,010,011

Type graph

Type relations for List
perl6-type-graph List List Cool Cool List->Cool Positional Positional List->Positional Iterable Iterable List->Iterable Mu Mu Any Any Any->Mu Cool->Any Slip Slip Slip->List Backtrace Backtrace Backtrace->List Array Array Array->List

Stand-alone image: vector, raster

Routines supplied by role Positional

List does role Positional, which provides the following methods:

(Positional) method of

method of()

Returns the type constraint for elements of the positional container. Defaults to Mu.

Routines supplied by role Iterable

List does role Iterable, which provides the following methods:

(Iterable) method iterator

Defined as:

method iterator() returns Iterator:D

Method stub that ensures all classes doing the Iterable role have a method iterator.

It is supposed to return an Iterator.

say (1..10).iterator;

(Iterable) method flat

Defined as:

method flat() returns Iterable

Returns another Iterable that flattens out all iterables that the first one returns.

For example

say (<a b>, 'c').elems;         # 2
say (<a b>, 'c').flat.elems;    # 3

because <a b> is a List and thus iterable, so (<a b>, 'c').flat returns ('a', 'b', 'c'), which has three elems.

Note that the flattening is recursive, so ((("a", "b"), "c"), "d").flat returns ("a", "b", "c", "d"), but it does not flatten itemized sublists:

say ($('a', 'b'), 'c').perl;    # ($("a", "b"), "c")

(Iterable) method lazy

Defined as:

method lazy() returns Iterable

Returns a lazy iterable wrapping the invocant.

say (1 ... 1000).is-lazy;      # False
say (1 ... 1000).lazy.is-lazy; # True

(Iterable) method hyper

Defined as:

method hyper(Int(Cool) :$batch = 64, Int(Cool) :$degree = 4) returns Iterable

Returns another Iterable that is potentially iterated in parallel, with a given batch size and degree of parallelism.

The order of elements is preserved.

say ([1..100].hyper.map({ $_ +1 }).list);

(Iterable) method race

Defined as:

method race(Int(Cool) :$batch = 64, Int(Cool) :$degree = 4) returns Iterable

Returns another Iterable that is potentially iterated in parallel, with a given batch size and degree of parallelism (number of parallel workers).

Unlike hyper, race does not preserve the order of elements.

say ([1..100].race.map({ $_ +1 }).list);

Routines supplied by class Cool

List inherits from class Cool, which provides the following methods:

(Cool) routine abs

Defined as:

sub abs(Numeric() $x)
method abs()

Coerces the invocant (or in the sub form, the argument) to Numeric and returns the absolute value (that is, a non-negative number).

say (-2).abs;       # 2
say abs "6+8i";     # 10

(Cool) method conj

Defined as:

method conj()

Coerces the invocant to Numeric and returns the complex conjugate (that is, the number with the sign of the imaginary part negated).

say (1+2i).conj;        # 1-2i

(Cool) routine sqrt

Defined as:

sub sqrt(Numeric(Cool) $x)
method sqrt()

Coerces the invocant to Numeric (or in the sub form, the argument) and returns the square root, that is, a non-negative number that, when multiplied with itself, produces the original number.

say 4.sqrt;             # 2
say sqrt(2);            # 1.4142135623731

(Cool) method sign

Defined as:

method sign()

Coerces the invocant to Numeric and returns its sign, that is, 0 if the number is 0, 1 for positive and -1 for negative values.

say 6.sign;             # 1
say (-6).sign;          # -1
say "0".sign;           # 0

(Cool) method rand

Defined as:

method rand()

Coerces the invocant to Num and returns a pseudo-random value between zero and the number.

say 1e5.rand;           # 33128.495184283

(Cool) routine sin

Defined as:

sub sin(Numeric(Cool))
method sin()

Coerces the invocant (or in the sub form, the argument) to Numeric, interprets it as radians, returns its sine.

say sin(0);             # 0
say sin(pi/4);          # 0.707106781186547
say sin(pi/2);          # 1

Note that Perl 6 is no computer algebra system, so sin(pi) typically does not produce an exact 0, but rather a very small floating-point number.

(Cool) routine asin

Defined as:

sub asin(Numeric(Cool))
method asin()

Coerces the invocant (or in the sub form, the argument) to Numeric, and returns its arc-sine in radians.

say 0.1.asin;               # 0.10016742116156
say asin(0.1);              # 0.10016742116156

(Cool) routine cos

Defined as:

sub cos(Numeric(Cool))
method cos()

Coerces the invocant (or in sub form, the argument) to Numeric, interprets it as radians, returns its cosine.

say 0.cos;                  # 1
say pi.cos;                 # -1
say cos(pi/2);              # 6.12323399573677e-17

(Cool) routine acos

Defined as:

sub acos(Numeric(Cool))
method acos()

Coerces the invocant (or in sub form, the argument) to Numeric, and returns its arc-cosine in radians.

(Cool) routine tan

Defined as:

sub tan(Numeric(Cool))
method tan()

Coerces the invocant (or in sub form, the argument) to Numeric, interprets it as radians, returns its tangent.

say tan(3);                 # -0.142546543074278
say 3.tan;                  # -0.142546543074278

(Cool) routine atan

Defined as:

sub atan(Numeric(Cool))
method atan()

Coerces the invocant (or in sub form, the argument) to Numeric, and returns its arc-tangent in radians.

say atan(3);                # 1.24904577239825
say 3.atan;                 # 1.24904577239825

(Cool) routine atan2

Defined as:

sub atan2(Numeric() $x, Numeric() $y = 1e0)
method atan2($y = 1e0)

Coerces the arguments (including the invocant in the method form) to Numeric, and returns their two-argument arc-tangent in radians.

say atan2(3);               # 1.24904577239825
say 3.atan2;                # 1.24904577239825

(Cool) method sec

Defined as:

sub sec(Numeric(Cool))
method sec()

Coerces the invocant (or in sub form, its argument) to Numeric, interprets it as radians, returns its secant, that is, the reciprocal of its cosine.

say 45.sec;                 # 1.90359440740442
say sec(45);                # 1.90359440740442

(Cool) routine asec

Defined as:

sub asec(Numeric(Cool))
method asec()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its arc-secant in radians.

say 0.45.sec;               # 1.11055940697373
say sec(0.45);              # 1.11055940697373

(Cool) routine cosec

Defined as:

sub cosec(Numeric(Cool))
method cosec()

Coerces the invocant (or in sub form, its argument) to Numeric, interprets it as radians, returns its cosecant, that is, the reciprocal of its sine.

say 0.45.cosec;             # 2.29903273150897
say cosec(0.45);            # 2.29903273150897

(Cool) routine acosec

Defined as:

sub acosec(Numeric(Cool))
method acosec()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its arc-cosecant in radians.

say 45.acosec;              # 0.0222240516182672
say acosec(45)              # 0.0222240516182672

(Cool) routine cotan

Defined as:

sub cotan(Numeric(Cool))
method cotan()

Coerces the invocant (or in sub form, its argument) to Numeric, interprets it as radians, returns its cotangent, that is, the reciprocal of its tangent.

say 45.cotan;               # 0.617369623783555
say cotan(45);              # 0.617369623783555

(Cool) routine acotan

Defined as:

sub acotan(Numeric(Cool))
method acotan()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its arc-cotangent in radians.

say 45.acotan;              # 0.0222185653267191
say acotan(45)              # 0.0222185653267191

(Cool) routine sinh

Defined as:

sub sinh(Numeric(Cool))
method sinh()

Coerces the invocant (or in method form, its argument) to Numeric, and returns its Sine hyperbolicus.

say 1.sinh;                 # 1.1752011936438
say sinh(1);                # 1.1752011936438

(Cool) routine asinh

Defined as:

sub asinh(Numeric(Cool))
method asinh()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its Inverse Sine hyperbolicus.

say 1.asinh;                # 0.881373587019543
say asinh(1);               # 0.881373587019543

(Cool) routine cosh

Defined as:

sub cosh(Numeric(Cool))
method cosh()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its Cosine hyperbolicus.

say cosh(0.5);              # 1.12762596520638

(Cool) routine acosh

Defined as:

sub acosh(Numeric(Cool))
method acosh()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its Inverse Cosine hyperbolicus.

say acosh(45);              # 4.4996861906715

(Cool) routine tanh

Defined as:

sub tanh(Numeric(Cool))
method tanh()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its Tangent hyperbolicus.

say tanh(30);               # 30

(Cool) routine atanh

Defined as:

sub atanh(Numeric(Cool))
method atanh()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its Inverse tangent hyperbolicus.

say atanh(0.5);              # 0.549306144334055

(Cool) routine sech

Defined as:

sub sech(Numeric(Cool))
method sech()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its Secant hyperbolicus.

say 0.sech;                 # 1

(Cool) routine asech

Defined as:

sub asech(Numeric(Cool))
method asech()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its Inverse hyperbolic secant.

say 0.8.asech;              # 0.693147180559945

(Cool) routine cosech

Defined as:

sub cosech(Numeric(Cool))
method cosech()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its Hyperbolic cosecant.

say cosech(pi/2);           # 0.434537208094696

(Cool) routine acosech

Defined as:

sub acosech(Numeric(Cool))
method acosech()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its Inverse hyperbolic cosecant.

say acosech(4.5);           # 0.220432720979802

(Cool) routine cotanh

Defined as:

sub cotanh(Numeric(Cool))
method cotanh()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its Hyperbolic cotangent.

say cotanh(pi);             # 1.00374187319732

(Cool) routine acotanh

Defined as:

sub acotanh(Numeric(Cool))
method acotanh()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns its Inverse hyperbolic cotangent.

say acotanh(2.5);           # 0.423648930193602

(Cool) routine cis

Defined as:

sub cis(Numeric(Cool))
method cis()

Coerces the invocant (or in sub form, its argument) to Numeric, and returns cos(argument) + i*sin(argument).

say cis(pi/4);              # 0.707106781186548+0.707106781186547i

(Cool) routine log

Defined as:

multi sub log(Numeric(Cool) $number, Numeric(Cool) $base?)
multi method log(Cool:D: Cool:D $base?)

Coerces the arguments (including the invocant in the method form) to Numeric, and returns its Logarithm to base $base, or to base e (Euler's Number) if no base was supplied (Natural logarithm.

say (e*e).log;              # 2

(Cool) routine log10

Defined as:

multi sub log10(Cool(Numeric))
multi method log10()

Coerces the invocant (or in the sub form, the invocant) to Numeric, and returns its Logarithm to base 10, that is, a number that approximately produces the original number when raised to the power of 10.

say log10(1001);            # 3.00043407747932

(Cool) method exp

Defined as:

multi sub exp(Cool:D $pow, Cool:D $base?)
multi method exp(Cool:D: Cool:D $base?)

Coerces the arguments (including the invocant in the method from) to Numeric, and returns $base raised to the power of the first number. If no $base is supplied, e (Euler's Number) is used.

say 0.exp;      # 1
say 1.exp;      # 2.71828182845905
say 10.exp;     # 22026.4657948067

(Cool) method unpolar

Defined as:

method unpolar(Numeric(Cool))

Coerces the arguments (including the invocant in the method form) to Numeric, and returns a complex number from the given polar coordinates. The invocant (or the first argument in sub form) is the magnitude while the argument (i.e. the second argument in sub form) is the angle. The angle is assumed to be in radians.

say sqrt(2).unpolar(pi/4);      # 1+1i

(Cool) routine round

Defined as:

multi sub round(Numeric(Cool))
multi method round(Cool:D: $unit = 1)

Coerces the invocant (or in sub form, its argument) to Numeric, and rounds it to the unit of $unit. If $unit is 1, rounds to the nearest integer.

say 1.7.round;          # 2
say 1.07.round(0.1);    # 1.1
say 21.round(10);       # 20

(Cool) routine floor

Defined as:

multi sub floor(Numeric(Cool))
multi method floor

Coerces the invocant (or in sub form, its argument) to Numeric, and rounds it downwards to the nearest integer.

say "1.99".floor;       # 1
say "-1.9".floor;       # -2
say 0.floor;            # 0

(Cool) routine ceiling

Defined as:

multi sub ceiling(Numeric(Cool))
multi method ceiling

Coerces the invocant (or in sub form, its argument) to Numeric, and rounds it upwards to the nearest integer.

say "1".ceiling;        # 1
say "-0.9".ceiling;     # 0
say "42.1".ceiling;     # 43

(Cool) routine truncate

Defined as:

multi sub truncate(Numeric(Cool))
multi method truncate()

Coerces the invocant (or in sub form, its argument) to Numeric, and rounds it towards zero.

say 1.2.truncate;       # 1
say truncate -1.2;      # -1

(Cool) routine ord

Defined as:

sub ord(Str(Cool))
method ord()

Coerces the invocant (or in sub form, its argument) to Str, and returns the Unicode code point number of the first code point.

say 'a'.ord;            # 97

The inverse operation is chr.

Mnemonic: returns an ordinal number

(Cool) routine chr

Defined as:

sub chr(Int(Cool))
method chr()

Coerces the invocant (or in sub form, its argument) to Int, interprets it as a Unicode code points, and returns a string made of that code point.

say '65'.chr;       # A

The inverse operation is ord.

Mnemonic: turns an integer into a character.

(Cool) routine chars

Defined as:

sub chars(Str(Cool))
method chars()

Coerces the invocant (or in sub form, its argument) to Str, and returns the number of characters in the string. Please note that on the JVM, you currently get codepoints instead of graphemes.

say 'møp'.chars;    # 3

(Cool) routine codes

Defined as:

sub codes(Str(Cool))
method codes()

Coerces the invocant (or in sub form, its argument) to Str, and returns the number of Unicode code points.

say 'møp'.codes;    # 3

(Cool) routine flip

Defined as:

sub flip(Str(Cool))
method flip()

Coerces the invocant (or in sub form, its argument) to Str, and returns a reversed version.

say 421.flip;       # 124

(Cool) routine trim

Defined as:

sub trim(Str(Cool))
method trim()

Coerces the invocant (or in sub form, its argument) to Str, and returns the string with both leading and trailing whitespace stripped.

my $stripped = '  abc '.trim;
say "<$stripped>";          # <abc>

(Cool) routine trim-leading

Defined as:

sub trim-leading(Str(Cool))
method trim-leading()

Coerces the invocant (or in sub form, its argument) to Str, and returns the string with leading whitespace stripped.

my $stripped = '  abc '.trim-leading;
say "<$stripped>";          # <abc >

(Cool) routine trim-trailing

Defined as:

sub trim-trailing(Str(Cool))
method trim-trailing()

Coerces the invocant (or in sub form, its argument) to Str, and returns the string with trailing whitespace stripped.

my $stripped = '  abc '.trim-trailing;
say "<$stripped>";          # <  abc>

(Cool) routine lc

Defined as:

sub lc(Str(Cool))
method lc()

Coerces the invocant (or in sub form, its argument) to Str, and returns it case-folded to lower case.

say "ABC".lc;       # abc

(Cool) routine uc

Defined as:

sub uc(Str(Cool))
method uc()

Coerces the invocant (or in sub form, its argument) to Str, and returns it case-folded to upper case (capital letters).

say "Abc".uc;       # ABC

(Cool) routine tc

Defined as:

sub tc(Str(Cool))
method tc()

Coerces the invocant (or in sub form, its argument) to Str, and returns it with the first letter case-folded to title case (or where not available, upper case).

say "abC".tc;       # AbC

(Cool) routine tclc

Defined as:

sub tclc(Str(Cool))
method tclc()

Coerces the invocant (or in sub form, its argument) to Str, and returns it with the first letter case-folded to title case (or where not available, upper case), and the rest of the string case-folded to lower case..

say 'abC'.tclc;     # Abc

(Cool) routine wordcase

Defined as:

sub wordcase(Str(Cool) $input, :&filter = &tclc, Mu :$where = True)
method wordcase(:&filter = &tclc, Mu :$where = True)

Coerces the invocant (or in sub form, the first argument) to Str, and filters each word that smart-matches against $where through the &filter. With the default filter (first character to upper case, rest to lower) and matcher (which accepts everything), this title-cases each word:

say "perl 6 programming".wordcase;      # Perl 6 Programming

With a matcher:

say "have fun working on perl".wordcase(:where({ .chars > 3 }));
                                        # Have fun Working on Perl

With a customer filter too:

say "have fun working on perl".wordcase(:filter(&uc), :where({ .chars > 3 }));
                                        # HAVE fun WORKING on PERL

(Cool) routine samecase

Defined as:

sub samecase(Cool $string, Cool $pattern)
method samecase(Cool:D: Cool $pattern)

Coerces the invocant (or in sub form, the first argument) to Str, and returns a copy of $string with case information for each individual character changed according to $pattern. (The pattern string can contain three types of characters, i.e. uppercase, lowercase and caseless. For a given character in $pattern its case information determines the case of the corresponding character in the result.) If $string is longer than $pattern, the case information from the last character of $pattern is applied to the remaining characters of $string.

say "perL 6".samecase("A__a__"); # Perl 6
say "pERL 6".samecase("Ab");     # Perl 6

(Cool) routine uniname

Defined as:

sub uniname(Str(Cool)) returns Str
method uniname() returns Str

Interprets the invocant / first argument as a Str, and returns the Unicode codepoint name of the first character. To convert a whole string use uninames.

# Camelia in Unicode
say ‘»ö«’.comb».uniname;
# «("RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK",
#   "LATIN SMALL LETTER O WITH DIAERESIS", "LEFT-POINTING DOUBLE ANGLE QUOTATION MARK")␤»

# Find the char with the longest Unicode name.
say (0..0x1FFFF).sort(*.uniname.chars)[*-1].chr.uniname;
# «ARABIC LIGATURE UIGHUR KIRGHIZ YEH WITH HAMZA ABOVE WITH ALEF MAKSURA INITIAL FORM␤»

(Cool) routine uninames

Defined as:

sub uninames(Str:D)
method uninames()

Returns of a Seq of unicode names for the Str provided.

dd ‘»ö«’.comb».uniname;
# «("RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK",
#  "LATIN SMALL LETTER O WITH DIAERESIS",
#  "LEFT-POINTING DOUBLE ANGLE QUOTATION MARK").Seq␤»

(Cool) routine chop

Defined as:

sub chop(Str(Cool))
method chop()

Coerces the invocant (or in sub form, its argument) to Str, and returns it with the last character removed.

say 'perl'.chop;                        # per

(Cool) routine chomp

Defined as:

sub chomp(Str(Cool))
method chomp()

Coerces the invocant (or in sub form, its argument) to Str, and returns it with the last character removed, if it is a logical newline.

say 'ab'.chomp.chars;                   # 2
say "a\n".chomp.chars;                  # 1

(Cool) routine substr

Defined as:

sub substr(Str(Cool) $str, $from, $chars?)
method substr($from, $chars?)

Coerces the invocant (or in the sub form, the first argument) to Str, and returns the string starting from offset $from. If $chars is supplied, at most $chars characters are returned.

say 'zenith'.substr(2);         # nith
say 'zenith'.substr(0, 3);      # zen

# works on non-strings too:
say 20151224.substr(6);         # 24

# sub form:
say substr "zenith", 0, 3;      # zen

If the $from parameter is a Callable, it is called with the number of chars in the string as argument. This allows easy indexing relative to the end:

say 20151224.substr(*-2);       # 24

(Cool) routine ords

Defined as:

sub ords(Str(Cool) $str)
method ords()

Coerces the invocant (or in the sub form, the first argument) to Str, and returns a list of Unicode codepoints for each character.

say "Perl 6".ords;              # 80 101 114 108 160 54
say ords 10;                    # 49 48

This is the list-returning version of ord. The inverse operation in chrs.

(Cool) routine chrs

Defined as:

sub chrs(*@codepoints) returns Str:D
method chrs()

Coerces the invocant (or in the sub form, the argument list) to a list of integers, and returns the string created by interpreting each integer as a Unicode codepoint, and joining the characters.

say <80 101 114 108 160 54>.chrs;   # Perl 6

This is the list-input version of chr. The inverse operation is ords.

(Cool) routine split

Defined as:

multi sub    split(  Str:D $delimiter, Str(Cool) $input, $limit = Inf, :$k, :$v, :$kv, :$p, :$skip-empty)
multi sub    split(Regex:D $delimiter, Str(Cool) $input, $limit = Inf, :$k, :$v, :$kv, :$p, :$skip-empty)
multi method split(  Str:D $delimiter, $limit = Inf, :$k, :$v, :$kv, :$p, :$skip-empty)
multi method split(Regex:D $delimiter, $limit = Inf, :$k, :$v, :$kv, :$p, :$skip-empty)

Coerces the invocant (or in the sub form, the second argument) to Str, and splits it into pieces based on delimiters found in the string.

If $delimiter is a string, it is searched for literally and not treated as a regex.

say split(';', "a;b;c").perl;          # ("a", "b", "c")
say split(';', "a;b;c", 2).perl;       # ("a", "b;c").Seq

say split(';', "a;b;c,d").perl;        # ("a", "b", "c,d")
say split(/\;/, "a;b;c,d").perl;       # ("a", "b", "c,d")
say split(/<[;,]>/, "a;b;c,d").perl;   # ("a", "b", "c", "d")

By default, split omits the matches, and returns a list of only those parts of the string that did not match. Specifying one of the :k, :v, :kv, :p adverbs changes that. Think of the matches as a list that is interleaved with the non-matching parts. :v interleaves the values of that list:

say 'abc'.split(/b/, :v);               # (a 「b」 c)

:k interleaves the keys, that is, the indexes:

say 'abc'.split(/b/, :k);               # (a 0 c)

:kv adds both indexes and matches:

say 'abc'.split(/b/, :kv);               # (a 0 「b」 c)

You can only use one of the :k, :v, :kv, :p adverbs in a single call to split.

and :p adds them as Pairs:

say 'abc'.split(/b/, :p)                # (a 0 => 「b」 c)

Note that unlike in Perl 5, empty chunks are not removed from the result list. For that behavior, use the `:skip-empty` named argument:

say ("f,,b,c,d".split: /","/             ).perl;  # ("f", "", "b", "c", "d")
say ("f,,b,c,d".split: /","/, :skip-empty).perl;  # ("f", "b", "c", "d")

See also: comb.

(Cool) routine lines

Defined as:

sub lines(Str(Cool))
method lines()

Coerces the invocant (and in sub form, the argument) to Str, decomposes it into lines (with the newline characters stripped), and returns the list of lines.

say lines("a\nb\n").join('|');          # a|b
say "some\nmore\nlines".lines.elems;    # 3

This method can be used as part of an IO::Path to process a file line-by-line, since IO::Path objects inherit from Cool, e.g.:

'huge-csv'.IO.lines -> $line {
    # Do something with $line
}

# or if you'll be processing later
my @lines = 'huge-csv'.IO.lines;

Without any arguments, sub lines operates on $*ARGFILES, which defaults to $*IN in the absence of any filenames.

To modify values in place use is copy to force a writeable container.

for $*IN.lines -> $_ is copy { s/(\w+)/{$0 ~ $0}/; .say }

(Cool) method words

Defined as:

method words(Int() $limit)

Coerces the invocant to Str, and returns a list of words that make up the string (and if $limit is supplied, only the first $limit words).

say 'The quick brown fox'.words.join('|');      # The|quick|brown|fox
say 'The quick brown fox'.words(2).join('|');   # The|quick

Only whitespace counts as word boundaries

say "isn't, can't".words.join('|');             # isn't,|can't

(Cool) routine comb

Defined as:

multi sub comb(Regex $matcher, Str(Cool) $input, $limit = *) returns List:D
multi method comb(Regex $matcher, $limit = *) returns List:D

Returns all (or if supplied, at most $limit) matches of the invocant (method form) or the second argument (sub form) against the Regex as a list of strings.

say "6 or 12".comb(/\d+/).join(", ");           # 6, 12

(Cool) method contains

multi method contains(Cool:D: Str(Cool) $needle, Cool $start?) returns True:D

Returns True if the invocant contains the $needle at any position within the string. If $start is provided skip as many characters.

say "Hello, World".contains('hello');      # False
say "Hello, World".contains(',');          # True

(Cool) routine index

Defined as:

multi sub    index(Str(Cool) $s, Str:D $needle, Int(Cool) $startpos = 0) returns Int
multi method index(Str(Cool) $needle, Int(Cool) $startpos = 0) returns Int

Coerces the first two arguments (in method form, also counting the invocant) to Str, and searches for $needle in the string starting from $startpos. It returns the offset into the string where $needle was found, and an undefined value if it was not found.

See the documentation in type Str for examples.

(Cool) routine rindex

Defined as:

multi sub    rindex(Str(Cool) $haystack, Str(Cool) $needle, Int(Cool) $startpos = $haystack.chars)
multi method rindex(Str(Cool) $haystack: Str(Cool) $needle, Int(Cool) $startpos = $haystack.chars)

Coerces the first two arguments (including the invocant in method form) to Str and $startpos to Int, and returns the last position of $needle in $haystack not after $startpos. Returns an undefined value if $needle wasn't found.

See the documentation in type Str for examples.

(Cool) method fmt

Defined as:

method fmt($format = '%s') returns Str:D

Uses $format to return a formatted representation of the invocant.

For more information about formats strings, see sprintf.

say 11.fmt('This Int equals %03d');               # This Int equals 011
say '16'.fmt('Hexadecimal %x');                   # Hexadecimal 10

(Cool) routine roots

Defined as:

multi sub roots(Numeric(Cool) $x, Int(Cool) $n)
multi method roots(Int(Cool) $n)

Coerces the first argument (and in method form, the invocant) to Numeric and the second ($n) to Int, and produces a list of $n Complex $n-roots, which means numbers that, raised to the $nth power, approximately produce the original number.

For example

my $original = 16;
my @roots = $original.roots(4);
say @roots;

for @roots -> $r {
    say abs($r ** 4 - $original);
}

produces this output:

2+0i 1.22464679914735e-16+2i -2+2.44929359829471e-16i -3.67394039744206e-16-2i
1.77635683940025e-15
4.30267170434156e-15
8.03651692704705e-15
1.04441561648202e-14

(Cool) method IO

Defined as:

method IO() returns IO::Path:D

Coerces the invocant to IO::Path.

.say for '.'.IO.dir;        # gives a directory listing

(Cool) routine EVAL

Defined as:

sub EVAL(Cool $code, :$lang = { ... })

Coerces the invocant to Str.

This works as-is with a literal string parameter. If you have a more complex input, such as a variable or string with embedded code, you must enable the MONKEY-SEE-NO-EVAL pragma:

use MONKEY-SEE-NO-EVAL;
EVAL "say { 5 + 5 }";   # says 10

Symbols in the current lexical scope are visible to code in an EVAL.

my $answer = 42;
EVAL 'say $answer;';    # says 42

However, since the set of symbols in a lexical scope is immutable after compile time, an EVAL can never introduce symbols into the surrounding scope.

EVAL 'my $lives = 9'; say $lives;   # error, $lives not declared

Furthermore, the EVAL is evaluated in the current package:

module M {
    EVAL 'our $answer = 42'
}
say $M::answer;         # says 42

And also the current language, meaning any added syntax is available:

sub infix:<mean>(*@a) is assoc<list> {
    @a.sum / @a.elems
}
EVAL 'say 2 mean 6 mean 4';     # says 4

An EVAL statement evaluates to the result of the last statement:

sub infix:<mean>(*@a) is assoc<list> {
    @a.sum / @a.elems
}
say EVAL 'say 1; 2 mean 6 mean 4';         # says 1, then says 4

EVAL is also a gateway for executing code in other languages:

EVAL "use v5.20; say 'Hello from perl5!'", :lang<Perl5>;

(Cool) routine EVALFILE

Defined as:

sub EVALFILE(Cool $filename, :$lang = { ... })

Slurps the specified file and evaluates it. Behaves the same way as EVAL with regard to both scoping and the $lang parameter. Evaluates to the value produced by the final statement in the file.

EVALFILE "foo.p6";

Routines supplied by class Any

List inherits from class Any, which provides the following methods:

(Any) method ACCEPTS

Defined as:

multi method ACCEPTS(Any:D: Mu $other)

Usage:

EXPR.ACCEPTS(EXPR);

Returns True if $other === self (i.e. it checks object identity).

Many built-in types override this for more specific comparisons

(Any) method any

Defined as:

method any() returns Junction:D

Interprets the invocant as a list and creates an any-Junction from it.

say so 2 == <1 2 3>.any;        # True
say so 5 == <1 2 3>.any;        # False

(Any) method all

Defined as:

method all() returns Junction:D

Interprets the invocant as a list and creates an all-Junction from it.

say so 1 < <2 3 4>.all;         # True
say so 3 < <2 3 4>.all;         # False

(Any) method one

Defined as:

method one() returns Junction:D

Interprets the invocant as a list and creates a one-Junction from it.

say so 1 == (1, 2, 3).one;      # True
say so 1 == (1, 2, 1).one;      # False

(Any) method none

Defined as:

method none() returns Junction:D

Interprets the invocant as a list and creates a none-Junction from it.

say so 1 == (1, 2, 3).none;     # False
say so 4 == (1, 2, 3).none;     # True

(Any) method list

Interprets the invocant as a list, and returns that List.

say 42.list.^name;           # List
say 42.list.elems;           # 1

(Any) method push

The method push is defined for undefined invocants and allows for autovivifying undefined to an empty Array, unless the undefined value implements Positional already. The argument provided will then be pushed into the newly created Array.

my %h;
dd %h<a>; # Any (and therefor undefined)
%h<a>.push(1); # .push on Any
dd %h; # «Hash %h = {:a($[1])}␤» # please note the Array

(Any) routine reverse

Defined as:

multi sub    reverse(*@list ) returns List:D
multi method reverse(List:D:) returns List:D

Returns a list with the same elements in reverse order.

Note that reverse always refers to reversing elements of a list; to reverse the characters in a string, use flip.

Examples:

say <hello world!>.reverse;     # (world! hello)
say reverse ^10;                # (9 8 7 6 5 4 3 2 1 0)

(Any) method sort

Sorts iterables with infix:<cmp> or given code object and returns a new List.

Examples:

say <b c a>.sort;                           # (a b c)
say 'bca'.comb.sort.join;                   # abc
say 'bca'.comb.sort({$^b cmp $^a}).join;    # cba
say '231'.comb.sort(&infix:«<=>»).join;     # 123

(Any) method map

Defined as:

proto method map(|) is nodal { * }
multi method map(\SELF: &block;; :$label, :$item)
multi method map(HyperIterable:D: &block;; :$label)

map will iterate over the invocant and apply the number of positional parameters of the code object from the invocant per call. The returned values of the code object will become elements of the returned Seq.

(Any) method deepmap

Defined as:

method deepmap(&block -->List) is nodal

deepmap will apply &block to each element and return a new List with the return values of &block, unless the element does the Iterable role. For those elements deepmap will descend recursively into the sublist.

dd [[1,2,3],[[4,5],6,7]].deepmap(*+1);
# OUTPUT«[[2, 3, 4], [[5, 6], 7, 8]]␤»

(Any) method duckmap

Defined as:

method duckmap(&block) is rw is nodal

duckmap will apply &block on each element and return a new list with defined return values of the block. For undefined return values, duckmap will try to descend into the element if that element implements Iterable.

my @a = [1,[2,3],4];
dd @a.duckmap({ $_ ~~ Int ?? $_++ !! Any });
# OUTPUT«(1, (2, 3), 4)␤»

(Any) method flat

Interprets the invocant as a list, flattens it, and returns that list. Please note that .flat will not solve the halting problem for you. If you flat an infinite list .flat may return that infinite list, eating all your RAM in the process.

say ((1, 2), (3)).elems;        # 2
say ((1, 2), (3)).flat.elems;   # 3

Please not that flat is not recursing into sub lists. You have to recurse by hand or reconsider your data structures. A single level of nesting can often be handled with destructuring in signatures. For deeper structures you may consider gather/take to create a lazy list.

my @a = [[1,2,3],[[4,5],6,7]];
sub deepflat(@a){
    gather for @a {
        take ($_ ~~ Iterable ?? deepflat($_).Slip !! $_)
    }
};
dd deepflat(@a);
# OUTPUT«(1, 2, 3, 4, 5, 6, 7).Seq␤»

(Any) method eager

Interprets the invocant as a list, evaluates it eagerly, and returns that list.

say (1..10).eager;              # (1 2 3 4 5 6 7 8 9 10)

(Any) method elems

Interprets the invocant as a list, and returns the number of elements in the list.

say 42.elems;                   # 1
say <a b c>.elems;              # 3

(Any) method end

Interprets the invocant as a list, and returns the last index of that list.

say 6.end;                      # 0
say <a b c>.end;                # 2

(Any) method pairup

method pairup() returns List

Interprets the invocant as a list, and constructs a list of pairs from it, in the same way that assignment to a Hash does. That is, it takes two consecutive elements and constructs a pair from them, unless the item in the key position already is a pair (in which case the pair is passed is passed through, and the next list item, if any, is considered to be a key again).

say (a => 1, 'b', 'c').pairup.perl;     # (:a(1), :b("c")).Seq

(Any) sub exit

sub exit(Int() $status = 0)

Exits the current process with return code $status.

Routines supplied by class Mu

List inherits from class Mu, which provides the following methods:

(Mu) routine defined

multi sub    defined(Mu) returns Bool:D
multi method defined()   returns Bool:D

Returns False on the type object, and True otherwise.

say Int.defined;                # False
say 42.defined;                 # True

Very few types (like Failure) override defined to return False even for instances:

sub fails() { fail 'oh noe' };
say fails().defined;            # False

(Mu) routine isa

multi method isa(Mu $type)      returns Bool:D
multi method isa(Str:D $type)   returns Bool:D

Returns True if the invocant is an instance of class $type, a subset type or a derived class (through inheritance) of $type.

my $i = 17;
say $i.isa("Int");   # True
say $i.isa(Any);     # True

A more idiomatic way to do this is to use the smartmatch operator ~~ instead.

my $s = "String";
say $s ~~ Str;       # True

(Mu) routine does

method does(Mu $type)      returns Bool:D

Returns True if and only if the invocant conforms to type $type.

my $d = Date.new('2016-06-03');
say $d.does(Dateish);             # True    (Date does role Dateish)
say $d.does(Any);                 # True    (Date is a subclass of Any)
say $d.does(DateTime);            # False   (Date is not a subclass of DateTime)

Using the smart match operator ~~ is a more idiomatic alternative.

my $d = Date.new('2016-06-03');
say $d ~~ Dateish;                # True
say $d ~~ Any;                    # True
say $d ~~ DateTime;               # False

(Mu) routine Bool

multi sub    Bool(Mu) returns Bool:D
multi method Bool()   returns Bool:D

Returns False on the type object, and True otherwise.

Many built-in types override this to be False for empty collections, the empty string or numerical zeros

say Mu.Bool;                    # False
say Mu.new.Bool;                # True
say [1, 2, 3].Bool;             # True
say [].Bool;                    # False
say { 'hash' => 'full'}.Bool;   # True
say {}.Bool;                    # False

(Mu) method Str

multi method Str()   returns Str

Returns a string representation of the invocant, intended to be machine readable. Method Str warns on type objects, and produces the empty string.

say Mu.Str;                     #!> use of uninitialized value of type Mu in string context

(Mu) routine gist

multi sub    gist(Mu) returns Str
multi method gist()   returns Str

Returns a string representation of the invocant, optimized for fast recognition by humans. As such lists will be truncated at 100 elements. Use .perl to get all elements.

The default gist method in Mu re-dispatches to the perl method for defined invocants, and returns the type name in parenthesis for type object invocants. Many built-in classes override the case of instances to something more specific that may truncate output.

gist is the method that say calls implicitly, so say $something and say $something.gist generally produce the same output.

say Mu.gist;        # (Mu)
say Mu.new.gist;    # Mu.new

(Mu) routine perl

multi sub    perl(Mu) returns Str
multi method perl()   returns Str

Returns a Perlish representation of the object (i.e., can usually be re-evaluated with EVAL to regenerate the object). The exact output of perl is implementation specific, since there are generally many ways to write a Perl expression that produces a particular value

(Mu) method clone

method clone(*%twiddles)

Creates a shallow clone of the invocant. If named arguments are passed to it, their values are used in every place where an attribute name matches the name of a named argument.

class Point2D {
    has ($.x, $.y);
    multi method gist(Point2D:D:) {
        "Point($.x, $.y)";
    }
}

my $p = Point2D.new(x => 2, y => 3);

say $p;                     # Point(2, 3)
say $p.clone(y => -5);      # Point(2, -5)

(Mu) method new

multi method new(*%attrinit)

Default method for constructing (create + initialize) new objects of a class. This method expects only named arguments which are then used to initialize attributes with accessors of the same name.

Classes may provide their own new method to override this default.

new triggers an object construction mechanism that calls submethods named BUILD in each class of an inheritance hierarchy, if they exist. See the documentation on object construction for more information.

(Mu) method bless

method bless(*%attrinit) returns Mu:D

Lower-level object construction method than new.

Creates a new object of the same type as the invocant, uses the named arguments to initialize attributes, and returns the created object.

You can use this method when writing custom constructors:

class Point {
    has $.x;
    has $.y;
    multi method new($x, $y) {
        self.bless(:$x, :$y);
    }
}
my $p = Point.new(-1, 1);

(Though each time you write a custom constructor, remember that it makes subclassing harder).

(Mu) method CREATE

method CREATE() returns Mu:D

Allocates a new object of the same type as the invocant, without initializing any attributes.

say Mu.CREATE.defined;  # True

(Mu) method print

multi method print() returns Bool:D

Prints value to $*OUT after stringification using .Str method without adding a newline at end.

"abc\n".print;          # abc␤

(Mu) method put

multi method put() returns Bool:D

Prints value to $*OUT after stringification using .Str method adding a newline at end.

"abc".put;              # abc␤

(Mu) method say

multi method say() returns Bool:D

Prints value to $*OUT after stringification using .gist method with newline at end. To produce machine readable output use .put.

say 42;                 # 42␤

(Mu) method ACCEPTS

multi method ACCEPTS(Mu:U: $other)

ACCEPTS is the method that smart matching with the infix ~~ operator and given/when invokes on the right-hand side (the matcher).

The Mu:U multi performs a type check. Returns True if $other conforms to the invocant (which is always a type object or failure).

say 42 ~~ Mu;           # True
say 42 ~~ Int;          # True
say 42 ~~ Str;          # False

Note that there is no multi for defined invocants; this is to allow autothreading of junctions, which happens as a fallback mechanism when no direct candidate is available to dispatch to.

(Mu) method WHICH

multi method WHICH() returns ObjAt:D

Returns an object of type ObjAt which uniquely identifies the object. Value types override this method which makes sure that two equivalent objects return the same return value from WHICH.

say 42.WHICH eq 42.WHICH;       # True

(Mu) method WHERE

method WHERE() returns Int

Returns an Int representing the memory address of the object.

(Mu) method WHY

multi method WHY()

Returns the attached Pod value. For instance,

sub cast(Spell $s)
#= Initiate a specified spell normally
#= (do not use for class 7 spells)
{
do-raw-magic($s);
}
say &cast.WHY;

prints

Initiate a specified spell normally (do not use for class 7 spells)

See the documentation specification for details about attaching Pod to variables, classes, functions, methods, etc.

(Mu) trait is export

multi sub trait_mod:<is>(Mu:U \type, :$export!)

Marks a type as being exported, that is, available to external users.

my class SomeClass is export { }

A user of a module or class automatically gets all the symbols imported that are marked as is export.

See Exporting and Selective Importing Modules for more details.

(Mu) method return

method return()

The method return will stop execution of a subroutine or method, run all relevant phasers and provide invocant as a return value to the caller. If a return type constraint is provided it will be checked unless the return value is Nil. A control exception is raised and can be caught with CONTROL.

sub f { (1|2|3).return };
dd f(); # OUTPUT«any(1, 2, 3)␤»

(Mu) method return-rw

Same as method return except that return-rw returns a writeable container to the invocant (see more details here: return-rw).

(Mu) method take

method take()

Takes the given item and passes it to the enclosing gather block.

#| randomly select numbers for lotto
my $num-selected-numbers = 6;
my $max-lotto-numbers = 49;
gather for ^$num-selected-numbers {
    take (1 .. $max-lotto-numbers).pick(1);
}.say;    #-> 32 22 1 17 32 9  (for example)

(Mu) method so

method so()

Returns a Bool value representing the logical non-negation of an expression. One can use this method similarly to the English sentence: "If that is so, then do this thing". For instance,

my @args = <-a -e -b -v>;
my $verbose-selected = any(@args) eq '-v' | '-V';
if $verbose-selected.so {
    say "Verbose option detected in arguments";
} #-> Verbose option detected in arguments

(Mu) method not

method not()

Returns a Bool value representing the logical negation of an expression. Thus it is the opposite of so.

my @args = <-a -e -b>;
my $verbose-selected = any(@args) eq '-v' | '-V';
if $verbose-selected.not {
    say "Verbose option not present in arguments";
} #-> Verbose option not present in arguments

Since there is also a prefix version of not, the above code reads better like so:

my @args = <-a -e -b>;
my $verbose-selected = any(@args) eq '-v' | '-V';
if not $verbose-selected {
    say "Verbose option not present in arguments";
} #-> Verbose option not present in arguments