[Haskell-cafe] Q about last&init

I am teaching myself haskell. The first impression is very good. But phrase "haskell is polynomially reducible" is making me sad :(. Anyway I am trying to backport my algorithm written in C. The key to performance is to have ability to remove element from the end of a list in O(1). But the original haskell functions last and init are O(n). My questions are: 1) Is last function is something like "black box" written in C++ which perform O(1)? So I shouldn't even try to imagine some haskell O(1) equivalent. 2) Or will optimizer (llvm?) reduce init&last complexity to 1? 3) Some people suggest to use sequences package, but still how do they implement O(1) init&last sequences equivalent in haskell? -- Regards, Marat.