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List::Operator::DoublePlus zef:tqdv last updated on 2022-02-23


Generated from DoublePlus.rakumod, then manually edited.




use List::Operator::DoublePlus;

# Concatenate two lists together
my @l  = @l1 ++ @l2;
my @l' = @l1 ⧺ @l2;

# The operator also works with Arrays and Slips


Provides a ++ operator to join or concatenate two lists together. The operator is also exported as its Unicode counterpart.

The concat subroutine that implements the operator's functionality is exported on demand using the sub tag.

This module is inspired by Aaron Sherman's Operator::Listcat which defines an infix listcat operator, as well as the infix (CIRCLED PLUS) Unicode alias.



The operator form of &concat.


The Unicode operator variant of ++.


multi sub concat(@a, @b --> List) multi sub concat(Slip \a, Slip \b --> Slip) multi sub concat(Array \a, Array \b --> Array)

Calls .Slip (which calls .list) on both arguments and applies the infix , operator to join them into a list.

For Slips, it returns a new Slip instead of a List.

For Arrays, it calls .append on the first parameter with the second parameter as its argument, and returns the combined array.

This subroutine also works for Seqs and any class that does PositionalBindFailover.



Same as :op, it exports the ++ operator and its Unicode counterpart ⧺.


Exports the ++ operator and its Unicode counterpart ⧺.


Exports the concat subroutine which implements the operator's functionality.


Only exports the ++ operator.


Only exports the Unicode operator.


The double plus was chosen as the list concatenation operator due to its similarity to the + operator applied to lists in Python an other languages. The ++ operator is also used to concatenate lists in Elixir, Haskell, and Scala. ++ was chosen over the @ operator used in OCaml as I thought it would be too close to the @ sigil. The Unicode counterpart ⧺ was inspired by this StackExchange question: Is there a common symbol for concatenating two (finite) sequences?


Tilwa Qendov


Licensed under the Artistic License 2.0.