signature Stack =
sig
  type a Stack

  val empty   : a Stack
  val isEmpty : a Stack -> bool

  val cons    : a * a Stack -> a Stack
  val head    : a Stack -> a
  val tail    : a Stack -> a Stack
end

structure List : Stack =
struct
  type a Stack = a list

  val empty = []
  fun isEmpty s = null s

  fun cons (x,s) = x :: s
  fun head s = hd s
  fun tail s = tl s
end
----

Error: stack.sml 3.10.
  Syntax error: inserting  AND.
Error: stack.sml 15.3.
  Syntax error: replacing  TYPE with  FUN.
Error: stack.sml 5.17.
  Type constructor Stack given 1 argument but wants 0.
Error: stack.sml 6.17.
  Type constructor Stack given 1 argument but wants 0.
Error: stack.sml 8.21.
  Type constructor Stack given 1 argument but wants 0.
Error: stack.sml 8.32.
  Type constructor Stack given 1 argument but wants 0.
Error: stack.sml 9.17.
  Type constructor Stack given 1 argument but wants 0.
Error: stack.sml 10.17.
  Type constructor Stack given 1 argument but wants 0.
Error: stack.sml 10.28.
  Type constructor Stack given 1 argument but wants 0.
Error: stack.sml 15.20.
  Undefined variable list.
Error: stack.sml 13.18.
  Type Stack in signature but not in structure.
Error: stack.sml 13.18.
  Type a in signature but not in structure.
Error: stack.sml 13.18.
  Variable type in structure disagrees with signature.
    variable: empty
    structure: [??? list]
    signature: [exn]
Error: stack.sml 13.18.
  Variable type in structure disagrees with signature.
    variable: isEmpty
    structure: [??? list] -> _
    signature: [exn] -> _
Error: stack.sml 13.18.
  Variable type in structure disagrees with signature.
    variable: tail
    structure: [??? list] -> [??? list]
    signature: [exn] -> [exn]