[Haskell-cafe] Q about last&init

[Закиров Марат]

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.