Fibonacci in CPS style

fibonacci_CPS.hs

fib :: Int -> Int
fib n = inner n (\x -> x) where -- setup the identity function for the base cases
   inner :: Int -> (Int -> Int) -> Int
   inner 0 cont = cont 0 -- base case for fibonacci, first two number are known
   inner 1 cont = cont 1
   -- 1st : function is tail recursive, so we call inner no matter what
   --      we have to progress to the base case, so we decrement n
   --      since fib n = fib (n-1) + fib (n-2), we already have the call to (n-1)
   --      and have to add the call to (n-2)
   --      the call to inner (n-2) also need a continuation function, which is juste x + y since both (n-1) and (n-2) have to be summed
   inner n cont = inner (n-1) (\x -> inner (n-2) (\y -> x + y))