List.filter: def of Base
Import: import Base
Lines 1063-1068 of Base/base.bend: https://jend.leeeet.dev/read.txt?path=Base/base.bend&start_line=1063&end_line=1068

import Base

def List.filter(~A: Data, ~f: A -> Bool, xs: List<&2, A>) -> List<&2, A>:
  match xs:
    case Nil{}:
      Nil{}
    case +h <> t:
      List.filter.put(A, h, List.filter(~A, ~f, t), f(h))

Uses (3):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List.filter.put