| II is where I'd like to be able to distinguish variables, constants, | and complex expressions in the left-hand sides of RULES, and | I and III are where I'd like control over the rewrite strategy, as | in strategy combinators. I'm deep in icfp submissions, so no time to reply properly. You can distinguish between literals, variables etc, in GHC's BuiltinRules. These are not hard to write: see prelude/PrelRules. But they are built in, not part of the source program. Maybe that's ok, since you are messing with built-in arithmetic. Another avenue is to elaborate the language of rules somehow to let you say what you want. But I don't know a good *spec* for such a feature, let alone an impl. Another possibility is to write a Core-to-Core optimiser aimed at your target area. Max B's plugins would let you dynamically link that to a distributed GHC. But it's not in the HEAD yet... Simon