⍣\ — Historyf⍣\N Y: states 0…N, including Y. Negative N steps through the inverse. Dyadic calls hold X fixed.
(1∘+)⍣\3⊢5 ⍝ 5 6 7 8
(1∘+)⍣\¯2⊢5 ⍝ 5 4 3
{1÷0}⍣\0⊢'ab' ⍝ 1 2⍴'ab'
f⍣\g Y stops when new g old is true. Includes initial and terminating states; always takes at least one step.
1 +⍣\{⍺=3}0 ⍝ 0 1 2 3
⊢⍣\≡⊢4 ⍝ 4 4
{⍵,1}⍣\2⊢,2 ⍝ 3 3⍴2 0 0 2 1 0 2 1 1
n←{0.5×⍵+2÷⍵} ⋄ ≢n⍣\≡⊢1 ⍝ 7x
States assemble with fill. ⍣ \ is the same operator; (f⍣p)\ is ordinary Scan.
RANK: nonscalar count; use Power. DOMAIN: non-integral count, non-Boolean predicate, unknown inverse.