/* define valid recursive types */

let
  /* define a list */
  type intlist = {hd : int, tl : intlist}

  /* define a tree */
  type tree = {key : int, children : treelist}
  type treelist = {hd : tree, tl : treelist}

  var lis : intlist := intlist { hd = 0, tl = nil }

in
  lis
end