Assignment: Difference between revisions

Jump to navigation Jump to search
1,700 bytes added ,  22:12, 10 September 2022
m
Text replacement - "</source>" to "</syntaxhighlight>"
m (fixed indentation)
m (Text replacement - "</source>" to "</syntaxhighlight>")
(4 intermediate revisions by the same user not shown)
Line 1: Line 1:
You can assign a value to a variable with the glyph: ''.
{{Built-in|Assignment|←}} allows associating a name with an [[array]] value. Some dialects also allow assignment of function and operator values using the assignment arrow. In [[defined functions]], assignment is global by default, but can be made local through explicit mention of the target name in the function header, or through dynamic [[shadow]]ing using <syntaxhighlight lang=apl inline>⎕SHADOW</syntaxhighlight>. In [[dfn]]s, assignments are local by default, but can be made global by explicit mention of the target namespace. Modified/indexed/selective assignment updates the most local definition.
==Examples==
===Basic usage===
Common examples (boxing on, and [[index origin]] is 0):
<syntaxhighlight lang=apl>
      ⎕←mat←(1 2 3)(1 2 3)
┌─────┬─────┐
│1 2 3│1 2 3│
└─────┴─────┘
</syntaxhighlight>
===Indexed assignment===
Individual elements can be updated using index assignment:
<syntaxhighlight lang=apl>
      mat[0]←1
      mat
┌─┬─────┐
│1│1 2 3│
└─┴─────┘
</syntaxhighlight>
A semicolon is necessary when dealing with a [[matrix]]:
<syntaxhighlight lang=apl>
      mat←3 3⍴⍳9
      mat
0 1 2
3 4 5
6 7 8
      mat[0 1;]
0 1 2
3 4 5
      mat[0 1;0 1]←0
      mat
0 0 2
0 0 5
6 7 8
</syntaxhighlight>
For higher-[[rank]] arrays, the number of semicolons needed is one less than the array rank.
===Modified assignment===
Some dialects allow placing a function the the immediate left of the assignment arrow:
<syntaxhighlight lang=apl>
      var←42
      var+←1
      var
43
</syntaxhighlight>
<syntaxhighlight lang=apl inline>var+←1</syntaxhighlight> is essentially equivalent to <syntaxhighlight lang=apl inline>1⊣var←var+1</syntaxhighlight> except that the result is [[shy]].
===Modified indexed assignment===
Modified assignment can also be combined with indexed assignment:
<syntaxhighlight lang=apl>
      mat←3 3⍴0
      mat
0 0 0
0 0 0
0 0 0
      mat[0 1;1]+←1
      mat
0 1 0
0 1 0
0 0 0
      mat[1;1],←'x'
      mat
0 1 0
0 x 0
0 0 0
</syntaxhighlight>
== External Links ==


Common examples (boxing on, and ⎕io is 0):
=== Documentation ===
    mat←(1 2 3)(1 2 3)
 
    mat
* [https://help.dyalog.com/latest/index.htm#Language/Primitive%20Functions/Assignment.htm Dyalog]
┌─────┬─────┐
* [https://microapl.com/apl_help/ch_020_010_110.htm APLX]
│1 2 3│1 2 3│
* J: [https://code.jsoftware.com/wiki/Vocabulary/eqdot local], [https://code.jsoftware.com/wiki/Vocabulary/eqco global]
└─────┴─────┘
{{APL built-ins}}[[Category:Primitive functions]]
    mat[0]←1  ⍝ indexed assignment
    mat
┌─┬─────┐
│1│1 2 3│
└─┴─────┘
    mat←3 3⍴⍳9
    mat
0 1 2
3 4 5
6 7 8
    mat[0 1;] ⍝ 1 semicolon is necessary when dealing with 2D arrays, 2 semicolons for 3D arrays etc.
0 1 2
3 4 5
    mat[0 1;0 1]←0
    mat
0 0 2
0 0 5
6 7 8
    ⍝ incrementing (or any dyadic function) parts of an array
    mat←3 3⍴0
    mat
0 0 0
0 0 0
0 0 0
    mat[0 1;1]+←1
    mat
0 1 0
0 1 0
0 0 0
    mat[1;1],←'x'
    mat
0 1 0
0 x 0
0 0 0

Navigation menu