\ — Expand / ScanN\Y expands the last axis. Positive counts consume and repeat an item; zero inserts one fill; negative counts insert |N| fills.
1 0 1\10 20 ⍝ 10 0 20
2 ¯2 1\10 20 ⍝ 10 10 0 0 20
f\Y scans left-to-right: each result becomes the next call’s left argument.
+\1 2 3 ⍝ 1 3 6
-\1 2 3 ⍝ 1 ¯1 ¯4
S f\Y starts with seed S, excluding the seed from the result.
10 -\1 2 3 ⍝ 9 7 4
100 +\10 20 ⍝ 110 130
The whole seed starts each lane. Use Rank for separate seeds per cell.
10 20 (+\⍤0 1)2 3⍴⍳6 ⍝ 2 3⍴11 13 16 24 29 35
(,10)+\1 2 3 ⍝ (,11⋄ ,13⋄ ,16)
Empty scans and unseeded singletons make no calls. [K] selects the axis; ⍀ defaults to the first.
APL difference: every scan left-accumulates, including dfns.