Editing Operator (computer programming) (section)

== Customization ==
Some languages support user-defined  [[operator overloading|overloading]] (such as [[C++]] and [[Fortran]]). An operator, defined by the language, can be [[function overloading|overloaded]] to behave differently based on the type of input.

Some languages (e.g. C, C++ and [[PHP]]) define a fixed set of operators, while others (e.g. [[Prolog]],<ref>{{Cite web|url=https://www.swi-prolog.org/pldoc/man?predicate=op/3|title=SWI-Prolog -- op/3|website=www.swi-prolog.org}}</ref> [[Seed7]],<ref>{{Cite web|url=http://seed7.sourceforge.net/examples/operator.htm|title=Declare an operator|website=seed7.sourceforge.net}}</ref> [[F Sharp (programming language)|F#]], [[OCaml]], [[Haskell]]) allow for user-defined operators. Some programming languages restrict operator symbols to special characters like {{mono|1='''[[Addition|+]]'''}} or {{mono|1='''[[Assignment (computer science)|:=]]'''}} while others allow names like <code>[[Integer_division#Division_of_integers|div]]</code> (e.g. [[Pascal (programming language)|Pascal]]), and even arbitrary names (e.g. [[Fortran]] where an upto 31 character long operator name is enclosed between dots<ref name="IntelFortran">{{cite web |title=Defined Operations |url=https://www.intel.com/content/www/us/en/docs/fortran-compiler/developer-guide-reference/2023-0/defined-operations.html |publisher=Intel |access-date=6 May 2025}}</ref>).

Most languages do not support user-defined operators since the feature significantly complicates parsing. Introducing a new operator changes the arity and precedence [[lexical specification]] of the language, which affects phrase-level [[lexical analysis]]. Custom operators, particularly via runtime definition, often make correct [[static analysis]] of a program impossible, since the syntax of the language may be Turing-complete, so even constructing the syntax tree may require solving the halting problem, which is impossible. This occurs for [[Perl]], for example, and some dialects of [[Lisp (programming language)|Lisp]].

If a language does allow for defining new operators, the mechanics of doing so may involve meta-programming {{endash}} specifying the operator in a separate language.