import
  sets

type
  AlwaysMatch = object

proc match(val: string, values: HashSet[string]): bool =
  val in values

proc match(val: string, predicate: proc(x: string): bool): bool =
  predicate(val)

template match(val: string, T: type AlwaysMatch): bool =
  true

proc walkDirRec(filter: auto = AlwaysMatch) =
  mixin match

  if match("dir_name", filter):
    echo "we have a match"
  else:
    echo "no match"

walkDirRec toHashSet(["foo", "bar", "baz"])
walkDirRec toHashSet(["file_name", "dir_name"])

walkDirRec()

walkDirRec do (x: string) -> bool:
  echo "matching ", x
  return true

walkDirRec do (x: string) -> bool:
  echo "matching ", x
  return false