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When weakening (or strengthening), chain the operation n times.

You may achieve this without extra newtypes by nesting uses of SW. However, strongweak generics can't handle this, forcing you to write manual instances.

SWChain provides this nesting behaviour in a type. In return for adding a boring newtype layer to the strong representation, you can chain weakening and strengthenings without having to write them manually.

The type works as follows:

Weakened (SWChain 0 a) = a
Weakened (SWChain 1 a) = Weakened a
Weakened (SWChain 2 a) = Weakened (Weakened a)
Weakened (SWChain n a) = WeakenedN n a

And so on. (This type is only much use from n = 2 onwards.)

You may also use this as a "via" type:

newtype A (s :: Strength) = A { a1 :: SW s (Identity (SW s Word8)) }
deriving via SWChain 2 (Identity Word8) instance     Weaken (A Strong)
deriving via SWChain 2 (Identity Word8) instance Strengthen (A Strong)