Assignment

←

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 shadowing using ⎕SHADOW. In dfns, 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):

   ⎕←mat←(1 2 3)(1 2 3)
┌─────┬─────┐
│1 2 3│1 2 3│
└─────┴─────┘

Indexed assignment

Individual elements can be updated using index assignment:

   mat[0]←1
   mat
┌─┬─────┐
│1│1 2 3│
└─┴─────┘
<source>
A semicolon is necessary when dealing with a [[matrix]]:
<source 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

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:

   var←42
   var+←1
   var
43

var+←1

is essentially equivalent to

1⊣var←var+1

except that the result is shy.

Modified indexed assignment

Modified assignment can also be combined with indexed assignment:

   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

External Links

Documentation

• Dyalog
• APLX
• J: local, global