Re: [Haskell-cafe] RFC: rewrite-with-location proposal

Immediately, the alternative of introducing bound variables in the environment that is available to rewrite rules comes to mind as a more general way of doing this. So this example from the GHC docs: {-# RULES "map/map" forall f g xs. map f (map g xs) = map (f.g) xs "map/append" forall f xs ys. map f (xs ++ ys) = map f xs ++ map f ys #-} For some source: map f (map g xs) it is translated into: let location = "somefile.hs:234" in map (f.g) xs So for error: {-# RULES "error/location" error s = errorLoc location s #-} is translated into: let location = "somefile.hs:345" in errorLoc location s Alexander