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{{Built-ins|Array notation|(⋄)|[⋄]}}, abbreviated '''APLAN''' parallel to [[wikipedia:JSON|JSON]], is a way to write most [[array]]s literally, with no or minimal use of [[primitive function]]s, possibly over multiple code lines. It differs from the [[strand notation]] existing since [[APL\360]] in that it can be used to write arrays of rank greater than one. Array notation is supported in [[dzaima/APL]], [[BQN]] (using angle brackets <code>⟨⋄⟩</code> instead of round parentheses <code>(⋄)</code>), and some tools for [[Dyalog APL]], where it is planned as an eventual language feature.
! [[Dyalog Ltd]] requests community feedback on the array notation in the hope of ending up with a notation that is shared with other dialects.<ref>Dyalog Ltd/Adám Brudzewsky. [https://forums.dyalog.com/viewtopic.php?f=13&t=1856&p=7431#p7431 Re: Deserialise-- does it work as expected?]. Dyalog Forums. 2022-09-05.</ref> Head to the [[Array notation design considerations|design considerations]] article for details!
 
Array notation generally consists of a vector notation written with parentheses <syntaxhighlight lang=apl inline>()</syntaxhighlight>, roughly equivalent to stranding, and a high-rank notation using square brackets <syntaxhighlight lang=apl inline>[]</syntaxhighlight>, indicating the [[Mix]] of a vector. It also supports [[namespace]]s, using <syntaxhighlight lang=apl inline>name:value</syntaxhighlight> syntax in round parentheses. [[Statement separator]]s must appear between elements and between [[wikipedia:name–value_pair|name–value pair]]s.
 
== Examples ==
 
Medium-sized array constants are often needed in code. Due to the lack of a native multi-line notation, programmers have resorted to various ad-hoc methods of approximating such, usually at the cost of reduced [[readability]]. A very common technique is repeated [[concatenate|concatenation]] resulting in the desired value being held in a variable (<syntaxhighlight lang=apl inline>z</syntaxhighlight> in the below examples), as opposed to array notation which can express the final value directly. In addition, the traditional technique sometimes involves the creation of helper variables as a side effect.
 
=== Basic arrays ===
 
{| class=wikitable
! Traditional method !! Array notation !! Description
|-
|<syntaxhighlight lang=apl>(0 6 1 8)(1 4 1 4 2)(2 7 1 8 2 8)(3 1 4 1 5)</syntaxhighlight>
|<syntaxhighlight lang=apl>(0 6 1 8 ⋄ 1 4 1 4 2 ⋄ 2 7 1 8 2 8 ⋄ 3 1 4 1 5)</syntaxhighlight>
|Vector of numeric vectors on a single line.
|-
|<syntaxhighlight lang=apl>z← (0 6 1 8)(1 4 1 4 2)
z,←(2 7 1 8 2 8)(3 1 4 1 5)</syntaxhighlight>
|<syntaxhighlight lang=apl>(0 6 1 8 ⋄ 1 4 1 4 2
2 7 1 8 2 8 ⋄ 3 1 4 1 5)</syntaxhighlight>
|Vector of numeric vectors split over two lines.
|-
|<syntaxhighlight lang=apl>z←,⊂'Three'
z,←⊂'Blind'
z,←⊂'Mice'</syntaxhighlight>
|<syntaxhighlight lang=apl>('Three'
'Blind'
'Mice')</syntaxhighlight>
|Vector of character vectors, one on each line. (The traditional method includes an unnecessary <syntaxhighlight lang=apl inline>,</syntaxhighlight> to indicate that <syntaxhighlight lang=apl inline>z</syntaxhighlight> will be a vector.)
|-
|<syntaxhighlight lang=apl>z←⍉⍪0 6 1 8
z⍪← 1 4 1 4
z⍪← 2 7 1 8
z⍪← 3 1 4 2</syntaxhighlight>
|<syntaxhighlight lang=apl>[0 6 1 8
1 4 1 4
2 7 1 8
3 1 4 2]</syntaxhighlight>
|Numeric matrix.
|-
|<syntaxhighlight lang=apl>z←⍪10
z⍪←20
z⍪←30
z⍪←40</syntaxhighlight>
|<syntaxhighlight lang=apl>[10
20
30
40]</syntaxhighlight>
|Column matrix.
|}
|}


{{Built-ins|Array notation|(⋄)|[⋄]}} is a way to write most [[array]]s literally, with no or minimal use of [[primitive function]]s, possibly over multiple code lines. It differs from the [[strand notation]] existing since [[APL\360]] in that it can be used to write arrays of rank greater than one. Array notation is supported in [[dzaima/APL]], [[BQN]] (using angle brackets <code>⟨⋄⟩</code> instead of round parentheses <code>(⋄)</code>), and some tools for [[Dyalog APL]], where it is planned as an eventual language feature.
=== Involved arrays ===
 
{| class=wikitable
! Traditional method !! Array notation !! Description
|-
|<syntaxhighlight lang=apl>a←⍉⍪0 0 1
a⍪← 1 0 1
a⍪← 0 1 1
z←,⊂a
a←⍉⍪0 1 1
a⍪← 1 1 0
a⍪← 0 1 0
z,←⊂a
a←⍉⍪0 1 1 1
a⍪← 1 1 1 0
z,←⊂a
a←⍉⍪0 1 1 0
a⍪← 1 0 0 1
a⍪← 0 1 1 0
z,←⊂a</syntaxhighlight>
|<syntaxhighlight lang=apl>([0 0 1
1 0 1
0 1 1]


Array notation generally consists of a vector notation written with parentheses <syntaxhighlight lang=apl inline>()</syntaxhighlight>, roughly equivalent to stranding, and a high-rank notation using square brackets <syntaxhighlight lang=apl inline>[]</syntaxhighlight>, indicating the [[Mix]] of a vector. It also supports [[namespace]]s, using <syntaxhighlight lang=apl inline>name:value</syntaxhighlight> syntax in round parentheses. [[Statement separator]]s must appear between elements and between [[wikipedia:name–value_pair|name–value pair]]s.
[0 1 1
  1 1 0
  0 1 0]


== Examples ==
[0 1 1 1
  1 1 1 0]


Medium-sized array constants are often needed in code. Due to the lack of a native multi-line notation, programmers have resorted to various ad-hoc methods of approximating such, usually at the cost of reduced [[readability]]. A very common technique is repeated [[concatenate|concatenation]]:
[0 1 1 0
<syntaxhighlight lang=apl>
  1 0 0 1
poss←1 2⍴'fns'  ((0 1)(0.7 0)(0.7 0)×size)
  0 1 1 0])</syntaxhighlight>
poss⍪←  'fnd'  ((0 1)(0  0)(0  0)×size)
|Vector of matrices.
poss⍪←  'lines'((0 0)(0.7 0)(0.7 0)×size)
|-
poss⍪←  'lnd'  ((0 0)(0  0)(0  0)×size)
|<syntaxhighlight lang=apl>z←⍉⍪0 'OK'
z⍪← 1 'WS FULL'
z⍪← 2 'SYNTAX ERROR'
z⍪← 3 'INDEX ERROR'
z⍪← 4 'RANK ERROR'</syntaxhighlight>
|<syntaxhighlight lang=apl>[0 'OK'
1 'WS FULL'
2 'SYNTAX ERROR'
3 'INDEX ERROR'
4 'RANK ERROR']</syntaxhighlight>
|Table with numeric and text columns.
|-
|<syntaxhighlight lang=apl>a←⍉⍪3 1 4
a⍪← 1 5 0
a←↑a
b←⍉⍪2 7 0
b⍪← 2 0 0
z←a,[0.5] b</syntaxhighlight>
|<syntaxhighlight lang=apl>[[3 1 4
  1 5 0]
[2 7 0
  2 0 0]]</syntaxhighlight>
|Rank 3 numeric array.
|-
|<syntaxhighlight lang=apl>a←,⊂3 1 4
a,←⊂1 5
a←↑a
b←,⊂2 7
b,← 2
b←↑b
z←↑a b</syntaxhighlight>
|<syntaxhighlight lang=apl>[[3
  1 5 9]
[2 7
  2]]</syntaxhighlight>
|Rank 3 numeric array relying on automatic padding with [[fill element]].
|-
|<syntaxhighlight lang=apl>
z←⍉⍪'fns'  ((0 1)(0.7 0)(0.7 0)×size)
z⍪← 'fnd'  ((0 1)(0  0)(0  0)×size)
z⍪← 'lines'((0 0)(0.7 0)(0.7 0)×size)
z⍪← 'lnd'  ((0 0)(0  0)(0  0)×size)
</syntaxhighlight>
</syntaxhighlight>
Array notation allows this multi-line construction to be made with a single assignment, and also provides an alternate syntax for the inner vectors of vectors:
|<syntaxhighlight lang=apl>
<syntaxhighlight lang=apl>
['fns'  ((0 1 ⋄ 0.7 0 ⋄ 0.7 0)×size)
poss←['fns'  ((0 1 ⋄ 0.7 0 ⋄ 0.7 0)×size)
'fnd'  ((0 1 ⋄ 0  0 ⋄ 0  0)×size)
      'fnd'  ((0 1 ⋄ 0  0 ⋄ 0  0)×size)
'lines'((0 0 ⋄ 0.7 0 ⋄ 0.7 0)×size)
      'lines'((0 0 ⋄ 0.7 0 ⋄ 0.7 0)×size)
'lnd'  ((0 0 ⋄ 0  0 ⋄ 0  0)×size)]
      'lnd'  ((0 0 ⋄ 0  0 ⋄ 0  0)×size)]
</syntaxhighlight>
</syntaxhighlight>
|Matrix of simple and nested vectors, with dynamic values.
|}
=== Namespaces ===
{| class=wikitable
! Traditional method !! Array notation !! Description
|-
|<syntaxhighlight lang=apl>⎕NS⍬</syntaxhighlight>
|<syntaxhighlight lang=apl>()</syntaxhighlight>
|Empty namespace.
|-
|<syntaxhighlight lang=apl>⎕NS¨⍬⍬⍬</syntaxhighlight>or<syntaxhighlight lang=apl>(⎕NS⍬)(⎕NS⍬)(⎕NS⍬)</syntaxhighlight>
|<syntaxhighlight lang=apl>()()()</syntaxhighlight>
|Vector of namespaces.
|-
|<syntaxhighlight lang=apl>z←⎕NS⍬
z.x←'hello'</syntaxhighlight>
|<syntaxhighlight lang=apl>(x:'hello')</syntaxhighlight>
|Namespace with character vector member.
|-
|<syntaxhighlight lang=apl>z←⎕NS⍬
z.x←⍉⍪'hello'
z.x⍪← 'world'</syntaxhighlight>
|<syntaxhighlight lang=apl>(x:['hello'
    'world'])</syntaxhighlight>
|Namespace with character matrix member.
|-
|<syntaxhighlight lang=apl>z←⎕NS⍬
z.y←⎕NS⍬
z.y.x←⍉⍪'hello'
z.y.x⍪← 'world'</syntaxhighlight>
|<syntaxhighlight lang=apl>(y:(x:['hello'
      'world']))</syntaxhighlight>
|Nested namespace structure with matrix member.
|-
|<syntaxhighlight lang=apl>z←⎕NS⍬
z.f←+
a←⎕NS⍬
a.f←-
z,←a
a←⎕NS⍬
a.f←×
z,←a
a←⎕NS⍬
a.f←÷
z←z.f</syntaxhighlight>
|<syntaxhighlight lang=apl>((f:+)(f:-)(f:×)(f:÷)).f</syntaxhighlight>
|[[Function array]].
|}
[[File:Array notation syntax.png|thumb|right|[[wikipedia:Railroad diagram|Railroad diagram]].]]
[[File:Array notation syntax.png|thumb|right|[[wikipedia:Railroad diagram|Railroad diagram]].]]
== Specification ==
== Specification ==
The notation consists of syntax that was invalid before its introduction, thus causing no issues for [[backwards compatibility]]. The added syntax consists of three constructs that are currently [[SYNTAX ERROR]]s:
The notation consists of syntax that was invalid before its introduction, thus causing no issues for [[backwards compatibility]]. The added syntax consists of three constructs that are currently [[SYNTAX ERROR]]s:
Line 61: Line 224:


The project manager Acre Desktop added support for the non-namespace parts of the notation in early 2018, together with Phil Last's original namespace notation, using square brackets and assignment arrow. [[dzaima/APL]] added support for vector notation with parentheses in 2018, namespaces and function arrays in 2019, and high-rank arrays with square brackets in 2020. [[BQN]] supported lists with angle brackets (<code>⟨</code>…<code>⟩</code>) in its initial implementation in 2020; square brackets (<code>[</code>…<code>]</code>) were reserved for high-rank array notation, which was implemented in 2022.
The project manager Acre Desktop added support for the non-namespace parts of the notation in early 2018, together with Phil Last's original namespace notation, using square brackets and assignment arrow. [[dzaima/APL]] added support for vector notation with parentheses in 2018, namespaces and function arrays in 2019, and high-rank arrays with square brackets in 2020. [[BQN]] supported lists with angle brackets (<code>⟨</code>…<code>⟩</code>) in its initial implementation in 2020; square brackets (<code>[</code>…<code>]</code>) were reserved for high-rank array notation, which was implemented in 2022.
On April 21, 2023, Dyalog Ltd published a blog post by Morten Kromberg announcing to the [[community]] the formal proposal for an APL array notation<ref name=formprop>Kromberg, Morten. [https://www.dyalog.com/blog/2023/04/formal-proposal-for-apl-array-notation-seeking-feedback/ Formal Proposal for APL Array Notation – Seeking Feedback]. Formal Proposal for APL Array Notation – Seeking Feedback. April 21, 2023.</ref> and by May 5, the specification for scoping in namespaces was changed due to feedback from Dyalog Ltd employee Peter Mikkelsen: Assignments inside value expressions would now affect the surrounding scope rather than having [[dfn]]-like auto-localisation, which can instead be achieved by wrapping the expression in an anonymous dfn.


{{Template:Comparison of array notations}}
{{Template:Comparison of array notations}}
== Documentation ==
== Documentation ==
* [https://mlochbaum.github.io/BQN/doc/arrayrepr.html#array-literals BQN] (as <code>⟨⋄⟩</code>, <code>[⋄]</code>, and <code>{key⇐val⋄}</code>)
* [https://mlochbaum.github.io/BQN/doc/arrayrepr.html#array-literals BQN] (as <code>⟨⋄⟩</code>, <code>[⋄]</code>, and <code>{key⇐val⋄}</code>)
* [https://www.nial-array-language.org/ndocs/NialDict2.html#bracket-comma-notation Nial] (as <code>[,]</code> for vectors)
* [https://www.nial-array-language.org/ndocs/NialDict2.html#bracket-comma-notation Nial] (as <code>[,]</code> for vectors)
== External links ==
== External links ==
* [https://abrudz.github.io/aplan/Formal%20Proposal%20%E2%80%94%20APL%20Array%20Notation.pdf Formal Proposal] document
* [https://abrudz.github.io/aplan Evaluate APL Array Notation] sandbox
* [https://abrudz.github.io/aplan Evaluate APL Array Notation] sandbox


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