libretto.lambda.util

Equality test where value equality of a: F[A], b: F[B] implies type equality A =:= B. I.e., value equality "clamps" A and B together.

Corollary: a value a: F[A] cannot also be assigned a type F[B] where B != A: testEqual(a: F[A], a: F[B]) results in Some[A =:= B].

Witnesses that F is a monad in the category of Scala functions.

Evidence that T is a singleton type, together with the single value of type T.

Type equality that, unlike Scala's =:=, can be pattern matched on.