Natural.lsum: def of bend-collections-laws-math@1.0.0.0
Import: import bend-collections-laws-math@1.0.0.0/spec/math/natural.bend as Natural
Lines 79-85 of bend-collections-laws-math@1.0.0.0/spec/math/natural.bend: https://jend.leeeet.dev/read.txt?path=bend-collections-laws-math@1.0.0.0/spec/math/natural.bend&start_line=79&end_line=85

import Base

# List.sum and List.prod as right folds
def lsum(xs: List<&2, Nat>) -> Nat:
  match xs:
    case Nil{}:
      0n
    case Con{x, t}:
      Nat.add(x, lsum(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=Base/base.bend&name=Nat.add