class Slip is List {}
A Slip is a List that automatically flattens into an outer List (or other list-like container or iterable).
For example it allows you to write a map that produces more than one value into the result without nesting:
say <a b c>.map({ ($_, $_.uc).Slip }).join('|'); # OUTPUT: «a|A|b|B|c|C»
In contrast, when returning an ordinary List, the resulting list is nested:
say <a b c>.map({ $_, $_.uc }).join('|'); # OUTPUT: «a A|b B|c C»
To create a Slip, either coerce another list-like type to it by calling the Slip method, or use the slip subroutine:
# This says "1" and then says "2", rather than saying "(1 2)" .say for gather { take slip(1, 2); }
A Slip may also be created by using the prefix:<|> operator. This differs from the slip subroutine in both precedence and treatment of single arguments. In fact, prefix:<|> only takes a single argument, so in that way, it behaves closer to the .Slip method than the slip subroutine.
my $l = (1, 2, 3); say (1, slip 2, 3).raku; # says (1, 2, 3) , slips 2, 3 into (1, …) say (0, slip $l, 4).raku; # says (0, $(1, 2, 3), 4) , $l does not break apart say (0, slip $l).raku; # says (0, 1, 2, 3) , slips from $l into (0, …) say (0, $l.Slip).raku; # says (0, 1, 2, 3) , slips from $l into (0, …) say (0, $l.Slip, 4).raku; # says (0, 1, 2, 3, 4) , slips from $l into (0, …, 4) say (|$l).raku; # says slip(1, 2, 3) , breaks apart $l say (0, (|$l, 4), 5); # says (0 (1 2 3 4) 5) , slips from $l into (…, 4) say (0, ($l.Slip, 4), 5); # says (0 (1 2 3 4) 5) , slips from $l into (…, 4) say (0, (slip $l, 4), 5); # says (0 (1 2 3) 4 5) , slips ($l, 4) into (0, …, 5) say (0, ($l, 4).Slip, 5); # says (0 (1 2 3) 4 5) , slips ($l, 4) into (0, …, 5)
Loops that do not want to produce a value for an iteration use Slips, rather than empty Lists to do so, as do if statements that do not run their blocks.
Please note that prefix:<|> will also apply parameters in a slippy manner to a routine call. It does not forward a Slip to the called routine, that includes return and take.
my \l = gather for 1..10 -> $a, $b { take |($a, $b) }; say l.raku; # OUTPUT: «((1, 2), (3, 4), (5, 6), (7, 8), (9, 10)).Seq» my \m= gather for 1..10 -> $a, $b { take ($a, $b).Slip }; say m.raku; # OUTPUT: «(1, 2, 3, 4, 5, 6, 7, 8, 9, 10).Seq»
Methods§
method List§
multi method List(Slip:D: --> List:D)
Turns it into a list.
sub slip§
multi slip(--> Empty) multi slip(@args --> Slip:D) multi slip(+args --> Slip:D)
Creates a Slip from its arguments by calling .Slip on the object formed by them. Returns Empty if called with void arguments.
Constants§
constant Empty§
Empty is a Slip of the empty List.
say "".comb ~~ Empty; # OUTPUT: «True»
For example, these constructs with a failing test return Empty:
do if 0 {}; (42 if 0); do with Any {}; (42 with Any);
Typegraph§
Slip