{-# RULES
"unpack"       [~1] forall a   . unpackCString# a             = build (unpackFoldrCString# a)
"unpack-list"  [1]  forall a   . unpackFoldrCString# a (:) [] = unpackCString# a
"unpack-append"     forall a n . unpackFoldrCString# a (:) n  = unpackAppendCString# a n

-- There's a built-in rule (in PrelRules.lhs) for
--      unpackFoldr "foo" c (unpackFoldr "baz" c n)  =  unpackFoldr "foobaz" c n

  #-}