Programmers can also create their own sigils. Other sigils include ~s for strings and ~D for dates. For example, ~r(foo) is a regular expression of "foo". In Elixir, sigils are provided via the " ~" symbol, followed by a letter to denote the type of sigil, and then delimiters. Similarly, constant names are prefixed with " #$" (pronounced "hash-dollar"). In CycL, variables are prefixed with a " ?" sigil. Similarly, some programmers surround constants with +. While this is only convention, and not enforced, the language itself adopts the practice (e.g., *standard-output*). In Common Lisp, special variables (with dynamic scope) are typically surrounded with * in what is called the " earmuff convention". In CLIPS, scalar variables are prefixed with a " ?" sigil, while multifield (e.g., a 1-level list) variables are prefixed with " $?". ", used with object attribute accessors (i.e., instance variables). Prominent examples of twigils in Raku include " ^", used with self-declared formal parameters ("placeholder variables"), and ". Raku also uses secondary sigils, or twigils, to indicate the scope of variables. In Perl, the sigils do not specify fine-grained data types like strings and integers, but the more general categories of scalars (using a prefixed " $"), arrays (using " hashes (using " %"), and subroutines (using " &"). Larry Wall adopted shell scripting's use of sigils for his Perl programming language. Many BASIC dialects use other sigils (like " %") to denote integers and floating-point numbers and their precision, and sometimes other types as well. Consequently, programmers outside America tend to pronounce $ as "string" instead of "dollar". The best known example of a sigil in BASIC is the dollar sign (" $") appended to the names of all strings. The use of sigils was popularized by the BASIC programming language. Sigils can be used to separate and demarcate namespaces that possess different properties or behaviors. Sigil, from the Latin sigillum, meaning a "little sign", means a sign or image supposedly having magical power. In computer programming, a sigil ( / ˈ s ɪ dʒ əl/) is a symbol affixed to a variable name, showing the variable's datatype or scope, usually a prefix, as in $foo, where $ is the sigil.
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