This package exports a single value, Useless, the sole member of the
sanctuary-useless/Useless type:
// Useless :: Useless
const Useless = require ('sanctuary-useless');Useless, as its name suggests, has no functionality. This makes it useful
for testing algebraic data types which satisfy various type classes.
The following assertion, in isolation, suggests that Identity a satisfies
Z.Setoid for all a:
eq (Z.Setoid.test (Identity (0))) (true);Identity Useless, though, does not satisfy Z.Setoid, indicating that
a is constrained in some way:
eq (Z.Setoid.test (Identity (Useless))) (false);
eq (Z.Setoid.test (Identity (0))) (true);Conversely, one can use Useless to demonstrate universal quantification
where applicable:
eq (Z.Functor.test (Identity (Useless))) (true);