Editing Named parameter (section)

== Optional parameters and positional parameters{{anchor|Optional_parameters}}==
{{Main article|Default argument}}
Named parameters are often used in conjunction with optional parameters.  Without named parameters, optional parameters can only appear at the end of the parameter list, since there is no other way to determine which values have been omitted.  In languages that support named optional parameters, however, programs may supply any subset of the available parameters, and the names are used to determine which values have been provided.

An added complication arises in languages such as [[OCaml]] that support both optional named parameters and [[partial application]]. It is impossible in general to distinguish between a function partly applied, and a function to which a subset of parameters have been provided.  OCaml resolves this ambiguity by requiring a positional argument after all optional named-parameter arguments: its presence or absence is used to decide if the function has been fully or partly applied. If all parameters are optional, the implementor may solve the issue by adding a dummy positional parameter of type [[Unit type|unit]].