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''' | A '''defined function''' (or '''tradfn''', for "traditional function", in [[Dyalog APL]]) is a function defined using a header that includes the function's name. Introduced in [[APL\360]], function definition was universally supported by APL dialects for much of the language's history, and is still commonly used in mainstream APLs. Since the 1990s other ways to [[Function styles|describe functions]] have appeared, with [[J]] and [[K]] rejecting function definition in favor of [[anonymous function]] description. Beginning in the 2010s [[Dyalog]]-based APL dialects including [[ngn/apl]], [[dzaima/APL]], and [[APL\iv]] have removed function definition in favor of [[dfn]]s. | ||
In many dialects the function header syntax of defined functions is adapted to allow '''defined operators''' as well. | |||
Tradfns allow both functional and procedural programming, and are essential | == Examples == | ||
== Representations == | |||
The canonical representation form is equivalent to what the user would type into the [[line editor]] to define the function. An alternative representation consists of the entire [[session]] log transcript after having such a definition has been made. A tradfn operator can also be called a '''tradop''' (pronounced "trad op"). | |||
== Properties == | |||
Tradfns allow both functional and procedural programming, and are essential for [[object-oriented programming]]. They support a full set of [[keyword]]s for flow control and object declarations. | |||
One of the most noticeable differences from dfns is that tradfns must declare their locals, because assignments are global by default. The declaration is done in a header line which also determines the function's name and calling syntax. Tradfns cannot be nested (although a tradfn can dynamically create other tradfns by [[Fix|"fixing"]] their source, and if the function thus created has a name which has been localised, it will only exist that scope) but ''can'' contain dfns. However, nested functions are less necessary due to tradfns using [[wikipedia:dynamic scoping|dynamic scoping]] as opposed to the lexical scoping of dfns. In other words, a tradfn can "see" locals of its caller. | One of the most noticeable differences from dfns is that tradfns must declare their locals, because assignments are global by default. The declaration is done in a header line which also determines the function's name and calling syntax. Tradfns cannot be nested (although a tradfn can dynamically create other tradfns by [[Fix|"fixing"]] their source, and if the function thus created has a name which has been localised, it will only exist that scope) but ''can'' contain dfns. However, nested functions are less necessary due to tradfns using [[wikipedia:dynamic scoping|dynamic scoping]] as opposed to the lexical scoping of dfns. In other words, a tradfn can "see" locals of its caller. | ||
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A tradfn can be [[niladic function|niladic]] which causes it to behave syntactically like an array. However, every time its name is referenced, it will run to create a result (if any). Such methods are often used to return a cache or as an entry point for the user. | A tradfn can be [[niladic function|niladic]] which causes it to behave syntactically like an array. However, every time its name is referenced, it will run to create a result (if any). Such methods are often used to return a cache or as an entry point for the user. | ||
== Comparison to dfns == | |||
Wikipedia has a comparison of [[Wikipedia:Direct_function#Dfns_versus_tradfns|dfns versus tradfns]]. | Wikipedia has a comparison of [[Wikipedia:Direct_function#Dfns_versus_tradfns|dfns versus tradfns]]. | ||
==External links== | ==External links== | ||
===Tutorials=== | ===Tutorials=== |