← — Assign
Keys: Alt-h
N←Y binds the name N to Y, an array, function or operator, and returns Y without displaying it. The target is the run just before ←, and the value is everything to its right. Independent assignments need ⋄, as in a←1 ⋄ b←2.
x←3 ⋄ x+2 ⍝ 5
x←1+2 × 3 ⋄ x ⍝ 9
sum←+/ ⋄ sum 1 2 3 ⍝ 6N f←Y sets N to N f Y. A named function goes in parentheses, N(f)←Y, because in N f←Y the target would be f. With nothing after the arrow, N f← sets N to f N.
x←10 ⋄ x+←3 ⋄ x ⍝ 13
f←× ⋄ x←3 ⋄ x(f)←4 ⋄ x ⍝ 12
x←1 2 3 ⋄ x⌽← ⋄ x ⍝ 3 2 1A target can also be a subscript such as x₁, a dot path such as T.a or x.[i], or a selection in parentheses, (f N), where f only selects or rearranges, as for structural Under. Modified assignment applies its function to each selected item. To apply a function to a selection as a whole, use Under, as in m(⌽@ 1⌷)← or m←⌽@ 1⌷ m. [a b]←Y destructures: each name gets the matching item.
x←1 2 3 ⋄ x₁←9 ⋄ x ⍝ 1 9 3
x←1 2 3 ⋄ x.[[0 2]]+←10 ⋄ x ⍝ 11 2 13
x←1 2 3 ⋄ (2↑x)←8 9 ⋄ x ⍝ 8 9 3
[a b]←10 20 ⋄ a+b ⍝ 30Inside a dfn, plain assignment is local. Modified and selective assignment update the nearest existing binding. Assignment covers every form.