+--------------------------------
+-- Cast propagation
+--------------------------------
+-- Try to move casts as much downward as possible.
+castprop, castproptop :: Transform
+castprop (Cast (Let binds expr) ty) = change $ Let binds (Cast expr ty)
+castprop expr@(Cast (Case scrut b _ alts) ty) = change (Case scrut b ty alts')
+ where
+ alts' = map (\(con, bndrs, expr) -> (con, bndrs, (Cast expr ty))) alts
+-- Leave all other expressions unchanged
+castprop expr = return expr
+-- Perform this transform everywhere
+castproptop = everywhere ("castprop", castprop)
+