Editing Raku (programming language) (section)

===Sigil invariance===
In Perl, [[Sigil (computer programming)|''sigils'']] &ndash; the punctuation characters that precede a variable name &ndash; change depending on how the variable is used:
 # Perl code
<!--Can't use tag "source lang" because of colorized emphasis on sigil-->
 my {{font color|red|@}}array = ('a', 'b', 'c');
 my $element = {{font color|red|$}}array[1];    # $element equals 'b',
 my @extract = {{font color|red|@}}array[1, 2]; # @extract equals ('b', 'c')
 my $element = {{font color|red|@}}array[1];    # 'b' comes with a warning (5.10 option)

In Raku, sigils are invariant, which means that they do not change based on whether it is the array or the array element that is needed:<ref name="syn2"/>
<!--Can't use tag "source lang" because of colorized emphasis on sigil-->
 # Raku code
 my {{font color|red|@}}array = 'a', 'b', 'c';
 my $element = {{font color|red|@}}array[1];    # $element equals 'b'
 my @extract = {{font color|red|@}}array[1, 2]; # @extract equals ('b', 'c')
 my @extract = {{font color|red|@}}array[1];    # @extract equals ('b')
The variance in Perl is inspired by number agreement in English and many other natural languages:

 "'''This''' apple."                    # $a        CORRECT
 "'''These''' apples."                  # @a        CORRECT
 "'''This''' third apple."              # $a[3]     CORRECT
 "'''These''' third apple."             # @a[3]     WRONG

However, this conceptual mapping breaks down when using [[Reference (computer science)|references]], since they may refer to data structures even though they are scalars. Thus, dealing with nested data structures may require an expression of both singular and plural form in a single term:

<!-- compare the following two code blocks by using the same style syntax-->
<syntaxhighlight lang="perl">
# Perl code: retrieve a list from the leaf of a hash containing hashes that contain arrays
my @trans_verbs = @{ $dictionary{ 'verb' }{ 'transitive' } };
</syntaxhighlight>

This complexity has no equivalent either in common use of natural language or in other programming languages,{{dubious|date=October 2015}} and it causes high [[cognitive load]] when writing code to manipulate complex data structures. This is the same code in Raku:
<syntaxhighlight lang="raku">
# Raku code: retrieve a list from the leaf of a hash containing hashes that contain arrays
my @trans_verbs = %dictionary<verb><transitive><>;
</syntaxhighlight>