lib/mlton/queue/list.fun

   1 (* Copyright (C) 1999-2006 Henry Cejtin, Matthew Fluet, Suresh
   2  *    Jagannathan, and Stephen Weeks.
   3  *
   4  * MLton is released under a BSD-style license.
   5  * See the file MLton-LICENSE for details.
   6  *)
   7 (*-------------------------------------------------------------------*)
   8 (*                             ListQueue                             *)
   9 (*-------------------------------------------------------------------*)
  10
  11 functor ListQueue(): BASIC_PERSISTENT_QUEUE =
  12 struct
  13
  14 structure L = List
  15
  16 datatype 'a t = T of 'a List.t
  17
  18 fun destruct(T l) =
  19    case L.destruct l of
  20       NONE => NONE
  21     | SOME(x, l) => SOME(x, T l)
  22
  23 fun empty () = T(L.empty())
  24
  25 fun isEmpty(T l) = L.isEmpty l
  26
  27 fun enque(T l, x) = T(L.append(l, L.single x))
  28
  29 end
  30
  31 structure ListQueue = PersistentQueue(ListQueue())