This topic has been discussed before, but here is a useful function that can be used to recursively traverse a list. This might be helpful when you need to seed an algorithm with a initial value, that cascades through the operation. The fibonacci performance seems to be quite good.
list ← {↑{⍺ ⍵}/⍵,'∘'}
∇Z ← A (L ltrav) B ;h;t
Z ← A ⍝ set output to accm before branch
→(B≡'∘')/0 ⍝ guard cond
(h t) ← B ⍝ head/tail
Z ← (A L h) (L ltrav) t ⍝ recursively call self w/ accumulated head and tail
∇
0 ({⍺+1} ltrav) list 1 2 3
⍝ fibonacci seq
1 ({⍺,(¯1↓¯2↑⍺)+¯1↑⍺} ltrav) list ⍳10
Cheers,