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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. | 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/System%20Functions/cr.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> | {{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/System%20Functions/cr.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> However, it should be noted that the <source lang=apl inline>∇</source>s are not part of the definition. Indeed, if using the [[Fix Definition]] (<source lang=apl inline>⎕FX</source>) [[system function]] to define the function, Dels need not (or must not, depending on implementation) be included. | ||
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]]. | 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]]. | ||
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</source> | </source> | ||
{{Works in|[[Dyalog APL]], [[APL2]], [[GNU APL]], [[NARS2000]], [[APLX]], and every older APL from [[APL\360]]}} | {{Works in|[[Dyalog APL]], [[APL2]], [[GNU APL]], [[NARS2000]], [[APLX]], and every older APL from [[APL\360]]}} | ||
=== Semi-colons === | |||
Assignments are global by default. To keep a name local, it must be mentioned in the header, separated from the rest of the header by a semi-colon: | |||
<source lang=apl> | |||
∇ r←l Tradfn r;intermediate | |||
intermediate←l r | |||
r←intermediate intermediate | |||
∇ | |||
</source> | |||
{{Works in|[[Dyalog APL]], [[APL2]], [[GNU APL]], [[NARS2000]], [[APLX]], and every older APL from [[APL\360]]}} | |||
=== Braces === | === Braces === | ||
An [[ambivalent function]] with an optional left argument, a conditional [[control structure]], one local variable, and a [[#Shyness|shy]] result: | An [[ambivalent function]] with an optional left argument, a conditional [[control structure]], one local variable, and a [[#Shyness|shy]] result: | ||
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==== Shyness ==== | ==== Shyness ==== | ||
By default, functions in APL will print their result to the session log even without using <source lang=apl inline>⎕←</source> unless their results are shy. Shy results are declared by putting curly braces around the result name (for example <source lang=apl inline>{result}←left Function right</source>). Assignment (<source lang=apl inline>name←array</source>) exhibits the same behaviour as a shy function in that, by default, no result is printed when the function terminates, but attempting to use the result still succeeds. | |||
==== Namelists ==== | ==== Namelists ==== | ||