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