Propiedades:
datatype cola= elem of int list;
val emptyQ = elem([]);

firstQ (queue emptyQ x) = x
firstQ (queue (queue q y) x) = y
dequeue (queue emptyQ x) = empty
isEmptyQ emptyQ = True
isEmpty (queue (emptyQ x)) = false
dequeue empty y firstQ empty no están definidos

Implementación:
fun firstQ (elem([])) = raise excep
| firstQ (elem(a::b)) = a;

fun queue (elem([]), y) = elem([y])
| queue (elem([x]), y)  = elem([x]@[y])
| queue (elem(x::z),  y) = elem(x::Z@[y]);

fun dequeue (elem([])) = raise excep
| dequeue (elem([a])) = emptyQ
| dequeue (elem(a::b)) = elem(b);

fun isEmpty (elem([])) = true
| isEmpty (elem(a)) = false;