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A '''dfn''' (pronounced "dee fun") is an alternative way to define a [[function]] and [[operator]], invented by [[John Scholes]]. A dfn operator can also be called a '''dop''' (pronounced "dee op"). | A '''dfn''' (contraction of '''direct function''' or '''dynamic function''', pronounced "dee fun") is an alternative way to define a [[function]] and [[operator]], invented by [[John Scholes]]. A dfn operator can also be called a '''dop''' (pronounced "dee op"). | ||
As of 2020, dfns are fully implemented in [[Dyalog APL]], [[NARS2000]], [[ngn/apl]], [[dzaima/APL]], and partially in [[GNU APL]]. | John Scholes was responsible for numerous presentations and publications on and about dfns, and until his passing he maintained the [[dfns workspace]], a collection of dfns examples. | ||
As of 2020, dfns are fully implemented in [[Dyalog APL]], [[NARS2000]], [[ngn/apl]], [[dzaima/APL]], and partially in [[GNU APL]], although not all dialects implement [[wikipedia:lexical scoping|lexical scoping]], in contrast to the dynamic scoping of [[tradfn]]s. In other words, a dfn cannot "see" locals of its caller, but can see locals of its definer. | |||
Wikipedia includes a thorough treatment of [[Wikipedia:dfns|dfns]]. | |||
== Examples == | |||
<source lang=apl> | |||
{⍵*0.5} 16 ⍝ square root | |||
4 | |||
3 {⍵*÷⍺} 27 ⍝ ⍺th root | |||
3 | |||
⍝ Multiline dfn with optional left parameter and conditional result | |||
root←{ | |||
⍺←2 ⍝ square root by default | |||
⍺=0:0 ⍝ return zero if zeroth root | |||
⍵*÷⍺ ⍝ result | |||
}</source> | |||
== External links == | == External links == | ||
* [[ | * [[wikipedia:Direct function|Direct function]] | ||
* [[ | |||
=== Tutorials === | |||
* APL Cultivation: [https://chat.stackexchange.com/rooms/52405/conversation/lesson-2-diving-into-functions-in-apl Diving Into Functions in APL] | |||
* Mastering Dyalog: [https://www.dyalog.com/uploads/documents/MasteringDyalogAPL.pdf#page=174 page 174] | |||
=== Documentation === | |||
* [https://help.dyalog.com/latest/#Language/Defined%20Functions%20and%20Operators/DynamicFunctions/Dynamic%20Functions%20and%20Operators.htm Dyalog] | |||
* [https://www.gnu.org/software/apl/apl.html#Section-3_002e7 GNU APL] | |||
{{APL syntax}} | {{APL syntax}}[[Category:Kinds of functions]][[Category:Defining functions]] | ||