Difference between revisions of "Dfn"
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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"). |
| − | 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> | ||
| + | |||
| + | === 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 == | ||
| − | * [[ | + | * [[wikipedia:Direct function|Direct function]] |
| − | * [[ | + | |
| − | {{APL syntax}} | + | === 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] | ||
| + | |||
| + | == References == | ||
| + | <references/> | ||
| + | |||
| + | {{APL syntax}}[[Category:Kinds of functions]][[Category:Defining functions]] | ||
Latest revision as of 12:27, 2 November 2020
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 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 lexical scoping, in contrast to the dynamic scoping of tradfns. In other words, a dfn cannot "see" locals of its caller, but can see locals of its definer.
Wikipedia includes a thorough treatment of dfns.
Examples
{⍵*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
}
Error-guards
Dyalog APL dfns support error-guards for processing errors by error codes.[1]
In the following example, there are two error-guards for the error code 11 (DOMAIN ERROR):[2]
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
External links
Tutorials
- APL Cultivation: Diving Into Functions in APL
- Mastering Dyalog: page 174
Documentation
References
- ↑ Error Guards – Dyalog APL.
- ↑ APL Error Messages and Codes – Dyalog APL.
