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Raku port of Perl's reverse() built-in


use P5reverse;

say reverse "Foo";  # ooF

with "Zippo" {
    say reverse();  # oppiZ, may need parens to avoid compilation error

say reverse 1,2,3;  # (3 2 1)

with 1,2,3 {
    say reverse();  # (3 2 1), may need parens to avoid compilation error


This module tries to mimic the behaviour of Perl's reverse built-in as closely as possible in the Raku Programming Language.


reverse LIST
        In list context, returns a list value consisting of the elements
        of LIST in the opposite order. In scalar context, concatenates the
        elements of LIST and returns a string value with all characters in
        the opposite order.

            print join(", ", reverse "world", "Hello"); # Hello, world

            print scalar reverse "dlrow ,", "olleH";    # Hello, world

        Used without arguments in scalar context, reverse() reverses $_.

            $_ = "dlrow ,olleH";
            print reverse;                         # No output, list context
            print scalar reverse;                  # Hello, world

        Note that reversing an array to itself (as in "@a = reverse @a")
        will preserve non-existent elements whenever possible; i.e., for
        non-magical arrays or for tied arrays with "EXISTS" and "DELETE"

        This operator is also handy for inverting a hash, although there
        are some caveats. If a value is duplicated in the original hash,
        only one of those can be represented as a key in the inverted
        hash. Also, this has to unwind one hash and build a whole new one,
        which may take some time on a large hash, such as from a DBM file.

            %by_name = reverse %by_address;  # Invert the hash


Context does not define behaviour

Whereas in Perl the type of context determines how reverse operates, in this implementation it's the type of parameter that determines the semantics. When given a List, it will revert the order of the elements. When given something that can coerce to a Str, it will return a string with the characters reversed in order.

$_ no longer accessible from caller's scope

In future language versions of Raku, it will become impossible to access the $_ variable of the caller's scope, because it will not have been marked as a dynamic variable. So please consider changing:


to either:


or, using the subroutine as a method syntax, with the prefix . shortcut to use that scope's $_ as the invocant:



Elizabeth Mattijsen liz@raku.rocks

If you like this module, or what I’m doing more generally, committing to a small sponsorship would mean a great deal to me!

Source can be located at: https://github.com/lizmat/P5reverse . Comments and Pull Requests are wereverseome.


Copyright 2018, 2019, 2020, 2021, 2023 Elizabeth Mattijsen

Re-imagined from Perl as part of the CPAN Butterfly Plan.

This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.