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


use P5fc;

say fc("FOOBAR") eq fc("FooBar"); # true

with "ZIPPO" {
    say fc();  # zippo, may need to use parens to avoid compilation error


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


fc      Returns the casefolded version of EXPR. This is the internal
        function implementing the "\F" escape in double-quoted strings.

        Casefolding is the process of mapping strings to a form where case
        differences are erased; comparing two strings in their casefolded
        form is effectively a way of asking if two strings are equal,
        regardless of case.

        Roughly, if you ever found yourself writing this

            lc($this) eq lc($that)    # Wrong!
                # or
            uc($this) eq uc($that)    # Also wrong!
                # or
            $this =~ /^\Q$that\E\z/i  # Right!

        Now you can write

            fc($this) eq fc($that)

        And get the correct results.

        Perl only implements the full form of casefolding, but you can
        access the simple folds using "casefold()" in Unicode::UCD and
        "prop_invmap()" in Unicode::UCD. For further information on
        casefolding, refer to the Unicode Standard, specifically sections
        3.13 "Default Case Operations", 4.2 "Case-Normative", and 5.18
        "Case Mappings", available at
        <http://www.unicode.org/versions/latest/>, as well as the Case
        Charts available at <http://www.unicode.org/charts/case/>.

        If EXPR is omitted, uses $_.

        This function behaves the same way under various pragma, such as
        within "use feature 'unicode_strings", as "lc" does, with the
        single exception of "fc" of LATIN CAPITAL LETTER SHARP S (U+1E9E)
        within the scope of "use locale". The foldcase of this character
        would normally be "ss", but as explained in the "lc" section, case
        changes that cross the 255/256 boundary are problematic under
        locales, and are hence prohibited. Therefore, this function under
        locale returns instead the string "\x{17F}\x{17F}", which is the
        LATIN SMALL LETTER LONG S. Since that character itself folds to
        "s", the string of two of them together should be equivalent to a
        single U+1E9E when foldcased.

        While the Unicode Standard defines two additional forms of
        casefolding, one for Turkic languages and one that never maps one
        character into multiple characters, these are not provided by the
        Perl core; However, the CPAN module "Unicode::Casing" may be used
        to provide an implementation.

        This keyword is available only when the "fc" feature is enabled,
        or when prefixed with "CORE::"; See feature. Alternately, include
        a "use v5.16" or later to the current 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/P5fc . Comments and Pull Requests are welcome.


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.