GHC.Core.TyCo.Compare

mayLookIdentical returns:

• An empty set if the two types are distinct unequal, and remain distinct even if we hide explicit kinds, runtime-reps, multiplicities.

• A non-empty set of invis_bits, if the two types might look equal, but are in fact distinct in the returned invis_bits.

See Note [mayLookIdentical], as well as Note [Showing invisible bits of types in error messages] in GHC.Tc.Errors.Ppr.

Make the sure the given invisible bits are displayed.

See Note [Showing invisible bits of types in error messages] in GHC.Tc.Errors.Ppr.

Something in a type which might be invisible.

Used to avoid reporting confusing errors to the user, like:

Couldn't match (a -> b) with (a -> b)

When in fact it is e.g. (a %1 -> b) vs (a %Many -> b), but the multiplicites have been suppressed.

See Note [Showing invisible bits of types in error messages] in GHC.Tc.Errors.Ppr.

A collection of InvisibleBits.