Help language development. Donate to The Perl Foundation

P5reverse cpan:ELIZABETH last updated on 2019-11-10



P5reverse - Implement 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 the reverse function of Perl as closely as possible.


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


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.


Elizabeth Mattijsen [email protected]

Source can be located at: . Comments and Pull Requests are wereverseome.


Copyright 2018-2019 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.