def evens

bend-mathlib@0.8.1.0 · perm.bend:189

import Base

189# The elements of a list at even positions (0, 2, 4, ...).
190def evens(-A: Data, xs: List<&2, A>) -> List<&2, A>:
191  match xs:
192    case Nil{}:
193      Nil{}
194    case +x <> r:
195      match r:
196        case Nil{}:
197          x <> Nil{}
198        case +y <> t:
199          x <> evens(A, t)