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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"). | 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"). | ||
John Scholes was responsible for numerous presentations and publications on and about dfns, and until his passing he maintained the [ | 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. | 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. | ||
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⍵*÷⍺ ⍝ result | ⍵*÷⍺ ⍝ result | ||
}</source> | }</source> | ||
=== Error-guards === | |||
Dyalog APL dfns support error-guards for processing errors by error codes.<ref>[https://help.dyalog.com/latest/#Language/Defined%20Functions%20and%20Operators/DynamicFunctions/Error%20Guards.htm Error Guards] – Dyalog APL.</ref> | |||
In the following example, there are two error-guards for the error code 11 (DOMAIN ERROR):<ref>[https://help.dyalog.com/latest/#Language/Errors/APL%20Errors.htm#APLErrors APL Error Messages and Codes] – Dyalog APL.</ref> | |||
<source lang=apl> | |||
Gravity←{ | |||
G←6.6743E¯11 ⍝ gravitational constant | |||
11::'N/A' ⍝ second DOMAIN ERROR: return 'N/A' | |||
11::∇⍎¨⍵ ⍝ first DOMAIN ERROR: maybe the argument is a vector of strings? | |||
G×⍵[1]×⍵[2]÷⍵[3]*2 ⍝ the argument is a vector of numbers | |||
} | |||
⍝ Calculate gravity force between the Earth and the Sun | |||
Gravity '1.99e30' '5.97e24' '1.50e11' | |||
3.524119391E22 | |||
Gravity 1.99e30 5.97e24 1.50e11 | |||
3.524119391E22 | |||
Gravity 1.99e30 5.97e24 0 ⍝ trigger division by zero | |||
N/A | |||
</source> | |||
== External links == | == External links == | ||
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* [https://help.dyalog.com/latest/#Language/Defined%20Functions%20and%20Operators/DynamicFunctions/Dynamic%20Functions%20and%20Operators.htm Dyalog] | * [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] | * [https://www.gnu.org/software/apl/apl.html#Section-3_002e7 GNU APL] | ||
== References == | |||
<references/> | |||
{{APL syntax}}[[Category:Kinds of functions]][[Category:Defining functions]] | {{APL syntax}}[[Category:Kinds of functions]][[Category:Defining functions]] |