An even simpler example, with just one module: ------------------------------------------------------- module Test where import Data.List (genericLength) {-# RULES "genericLength/length" genericLength = length #-} ------------------------------------------------------- D:\...\hask> ghc -O -fglasgow-exts --make Test.hs Chasing modules from: Test.hs Compiling Test ( Test.hs, ./Test.o ) D:\...\hask> ghc -O -fglasgow-exts --make Test.hs Chasing modules from: Test.hs Skipping Test ( Test.hs, ./Test.o ) tcLookupGlobal (id): `Data.List.genericLength' is not in scope When checking the transformation rule "genericLength/length" Surely that *must* be a bug, mustn't? Juanma