Any type that has a class constraint is called an overloaded type, and hence ourtriple
function is an overloaded function. We can even also specify a type variable without the class constraint, in which case that type is completely polymorphic and any type can fill the arguments' place. For example, this is used in several list functions we used earlier, as their results do not depend on the types of elements that fill the lists. For example, the head
(return the first element of a list) and tail
(return the list excluding the first element) functions must work regardless of what type the elements in the list are. Therefore, their type signatures are: