Perform the case-of-case transformation. This pushes case expressions into the case branches of other case expressions, which can often yield optimization opportunities.

Example: @ case (case s of { C1 a -> x; C2 b -> y; }) of D1 -> w D2 -> z

• ->

case s of C1 a -> case x of { D1 -> w; D2 -> z; } C2 b -> case y of { D1 -> w; D2 -> z; } @

We also transform

    case ((force ifThenElse) b (constr t) (constr f)) alts

into

    force (force ifThenElse b (delay (case (constr t) alts)) (delay (case (constr f) alts)))

This is always an improvement.