sum.mixml

type order = (() | () | ())
val less = @1[order]
val equal = @2[order]
val greater = @3[order]

val compare(n : int)(m : int) = if n == m then equal else if n < m then less else greater

do print(compare 4 5); print "\n"
do print(compare 7 7); print "\n"
do print(compare 100 0); print "\n"

type option[a] = (() | a)
val none[a] = @1[option[a]]
val some[a](x : a) = x@2[option[a]]

val nothing = none[string]
val just = some[string] "ho"
do print nothing; print "\n"
do print just; print "\n"

module ListD = link L = {type list[a]} with {data list[a] = (() | (a, L.list[a]))}

type list[a] = ListD.list[a]
val nil[a] = in ListD.list[a](()@1[(() | (a, list[a]))])
val cons[a](x : a)(xs : list[a]) = in ListD.list[a]((x, xs)@2[(() | (a, list[a]))])
val nili = nil[int]
val consi = cons[int]

val l = consi 3 (consi 5 (consi 0 (consi 2 nili)))
do print l; print "\n"

module LISTF = fn L = {type list[a]} in
{
  type list[a],
  val toList[a] : (() | (a, L.list[a])) -> list[a],
  val fromList[a] : list[a] -> (() | (a, L.list[a]))
}

unit LIST = link L = {type list[a]} with LISTF L

module List = link L = {type list[a]} with
![unit LISTF L seals {
  type list[a] = (() | (a, L.list[a])),
  val toList[a](l : list[a]) = l,
  val fromList[a](l : list[a]) = l
}]