I winged before about NOINLINE pragma on things defined locally in a where clause not doing what I expected: http://www.mail-archive.com/glasgow-haskell-users@haskell.org/msg10338.html Turns out that one was fixed in ghc HEAD. I've got another similar one which is not working as I expect in 6.6 or in head from 1st March. This example is from an experimental re-implementation of the Put monad in Data.Binary: write :: Int -> (Ptr Word8 -> IO ()) -> Put () write !n body = Put $ \c buf@(Buffer fp o u l) -> if n <= l then write' c fp o u l else write' (flushOld c n fp o u) (newBuffer c n) 0 0 0 where {-# NOINLINE write' #-} write' c !fp !o !u !l = -- warning: this is a tad hardcore B.inlinePerformIO (withForeignPtr fp (\p -> body $! (p `plusPtr` (o+u)))) `seq` c () (Buffer fp o (u+n) (l-n)) {-# INLINE [1] write #-} Then we use it with things like word8 :: Word8 -> Put () word8 !w = write 1 (pokeWord8 w) pokeWord8 :: Word8 -> Ptr Word8 -> IO () pokeWord8 w p = poke p w Then there's a rule so that things like: foo :: Word8 -> Put () foo !n = do word8 n word8 (n+1) word8 (n+17) get turned into a single call to write. Anyway, the point is that when we look at the stg/core we see that in write above, the write' has been inlined at the two call sites where as I want both branches of the if test to make calls to write'. The code is here: http://haskell.org/~duncan/binary/PutMonad.hs http://haskell.org/~duncan/binary/PutTest.hs the stg from ghc-6.6 is: http://haskell.org/~duncan/binary/PutTest.stg with ghc head from 1st March the result is different but still inlines write' in both branches. Duncan