Most directly: == defines equivalence classes within particular types (polymorphic over types fulfilling Eq). This means by definition it's domain is limited to

Most directly: == defines equivalence classes within particular types (polymorphic over types fulfilling Eq). This means by definition it's domain is limited to processes which result in a Eq-able type at which point it defines equality as equality of that final type. Your example only seems strange when you assume semantics of equality that are more dramatic than actually used.