Hi all, is it OK for containers to depend on ghc-prim package? The GHC documentation says not to use it, but it seems to me people are using it whenever they need :) I do not know whether there is any policy about that. Any comments, GHC HQ? The reason for that is unchecked bit shift. Data.Bits.shift[L|R] and GHC.Exts.shift[L|RL]# perform checks to ensure the shift is not by more than WORD_SIZE_IN_BITS. That does not sound like a big deal, but it causes unnecessary heap allocation that I could not reliably avoid. Using GHC.Prim.uncheckedShift[L|RL]# produces best code. Cheers, Milan PS: Dependency would be GHC-specific, non-GHC compilers use Data.Bits.shift[L|R].