List.swap_at: def of bendlib-kernel-list@1.0.0.0
Import: import bendlib-kernel-list@1.0.0.0/list.bend as List
Lines 17-27 of bendlib-kernel-list@1.0.0.0/list.bend: https://jend.leeeet.dev/read.txt?path=bendlib-kernel-list@1.0.0.0/list.bend&start_line=17&end_line=27

import Base

# Swap positions i and i+1.
def swap_at(-A: Data, +i: Nat, xs: List<&2, A>) -> List<&2, A>:
  match i:
    case 0n:
      swap_head(A, xs)
    case 1n+p:
      match xs:
        case Nil{}:
          Nil{}
        case +x <> t:
          x <> swap_at(A, p, t)

Uses (3):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=bendlib-kernel-list@1.0.0.0/list.bend&name=swap_head