Util.map_halves.go: def of unified-nsga-iii@0.2.2.0
Import: import unified-nsga-iii@0.2.2.0/util.bend as Util
Lines 275-300 of unified-nsga-iii@0.2.2.0/util.bend: https://jend.leeeet.dev/read.txt?path=unified-nsga-iii@0.2.2.0/util.bend&start_line=275&end_line=300

import Base

# Balanced fork-join map. Singleton / empty stay sequential. Fuel 0 is a
# total fallback (public callers pass |xs|). `~f` is a closed top-level.
# Mid take/drop is inlined: a computed pair cannot be matched.
def map_halves.go(
  ~A: Data,
  ~B: Data,
  ~C: Data,
  ~f: @+c:C -> @+x:A -> B,
  +ctx: C,
  +fuel: Nat,
  xs: List<&2, A>
) -> List<&2, B>:
  match fuel xs:
    case 0n Nil{}:
      Nil{}
    case 0n h <> t:
      f(ctx, h) <> map_halves.go(~A, ~B, ~C, ~f, ctx, 0n, t)
    case 1n+p Nil{}:
      Nil{}
    case 1n+p h <> Nil{}:
      f(ctx, h) <> Nil{}
    case 1n+p h <> t:
      +all = {h <> t : List<&2, A>}
      +mid = Nat.div(list_len(A, all), 2n)
      a b = map_halves.go(~A, ~B, ~C, ~f, ctx, p, List.take(&2, A, all, mid)) map_halves.go(~A, ~B, ~C, ~f, ctx, p, List.drop(&2, A, all, mid))
      List.append(&2, B, a, b)

Uses (7):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.append
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.drop
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.take
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.div
  https://jend.leeeet.dev/definition.txt?path=unified-nsga-iii@0.2.2.0/util.bend&name=list_len