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Defined function (traditional) (view source)
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A '''user-defined function''' (or '''tradfn''', pronounced "trad fun", 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. | A '''user-defined function''' (or '''tradfn''', pronounced "trad fun", 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. | ||
{{Anchor|Representations}}The canonical representation form is equivalent to what the user would type into the [[line editor]] to define the function.<ref>[[Dyalog Ltd.]] Programming Reference Guide. [https://help.dyalog.com/latest/#Language/Defined%20Functions%20and%20Operators/Canonical%20Representation.htm Canonical Representation].</ref> An alternative representation consists of the entire [[session]] log transcript, including [[Del]]s (<source lang=apl inline>∇</source>) and line numbers, after having such a definition has been made.<ref>[[Dyalog Ltd.]] Language Reference Guide. [https://help.dyalog.com/latest/#Language/System%20Functions/vr.htm Vector Representation].</ref> | |||
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. Wikipedia has a comparison of [[Wikipedia:Direct_function#Dfns_versus_tradfns|dfns versus tradfns]]. | |||
In many dialects the function header syntax of defined functions is adapted to allow user-defined [[operator]]s as well. A tradfn operator can also be called a '''tradop''' (pronounced "trad op"), parallel to how a "dfn" operator can be called a ''dop''. | In many dialects the function header syntax of defined functions is adapted to allow user-defined [[operator]]s as well. A tradfn operator can also be called a '''tradop''' (pronounced "trad op"), parallel to how a "dfn" operator can be called a ''dop''. | ||
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=== Brackets === | === Brackets === | ||
[[GNU APL]] allows functions and operators to accept an [[function axis|axis]] argument:<ref>[https://www.gnu.org/software/apl/apl.html#Section-3_002e2 | [[GNU APL]] allows functions and operators to accept an [[function axis|axis]] argument:<ref>[[GNU APL community]]. GNU APL Info Manual. [https://www.gnu.org/software/apl/apl.html#Section-3_002e2 Axis argument in defined functions].</ref> | ||
<source lang=apl> | <source lang=apl> | ||
∇ Z←Average[X] B | ∇ Z←Average[X] B | ||
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</source> | </source> | ||
{{Works in|[[Dyalog APL]], [[APL2]], [[GNU APL]], [[NARS2000]], [[APLX]]}} | {{Works in|[[Dyalog APL]], [[APL2]], [[GNU APL]], [[NARS2000]], [[APLX]]}} | ||
== Properties == | == Properties == | ||
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3 2 1 | 3 2 1 | ||
</source>{{Works in|[[Dyalog APL]]}} | </source>{{Works in|[[Dyalog APL]]}} | ||
== A+ == | === A+ differences=== | ||
[[A+]] uses a reworked style of function and operator definition than maintains the principle of a header that matches the way the function will be used, but differs in many details: | [[A+]] uses a reworked style of function and operator definition than maintains the principle of a header that matches the way the function will be used, but differs in many details: | ||
* The result name is not included in the header; instead, the result of the last executed statement is returned (and so functions that do not return a result cannot be defined). | * The result name is not included in the header; instead, the result of the last executed statement is returned (and so functions that do not return a result cannot be defined). | ||
* The header is separated from the body with a colon, and the body of a multi-line function is enclosed in curly braces. | * The header is separated from the body with a colon, and the body of a multi-line function is enclosed in curly braces. | ||
* Functions have lexical scope. Variables assigned are local by default, and can be made global by enclosing their names in parentheses when assigning. | * Functions have lexical scope. Variables assigned are local by default, and can be made global by enclosing their names in parentheses when assigning. | ||
==External links== | ==External links== | ||
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=== Documentation === | === Documentation === | ||
* [https://help.dyalog.com/latest/#Language/Introduction/Functions.htm | * Dyalog: [https://help.dyalog.com/latest/#Language/Introduction/Functions.htm Functions], [https://help.dyalog.com/latest/#Language/Introduction/Operators.htm Operators] | ||
* APLX: [http://microapl.com/apl_help/ch_020_010_070.htm User-defined Functions], [http://microapl.com/apl_help/ch_020_010_090.htm User-defined Operators] | |||
* [http://microapl.com/apl_help/ch_020_010_070.htm | |||
=== References === | === References === | ||