[Haskell-beginners] Translating a while

I'm learning Haskell and I'm trying to translate a pseudocode algorithm to generate the next permutation from a previous permutation. A permutation is a list of n numbers (let's call it a) in {1 .. n} appearing once in arbitrary order. The first step is to find the largest index j in the list for which a[j] < a[j+1]. The pseudocode is simple: j:= n-1 while a[j] > a[j+1] j:=j-1 I've coded a haskell function to do this, but it is much uglier than the pseudocode : j :: Integral a => [a] -> Int j [] = 0 j xs = if (head (tail (reverse xs)) < last xs) then (length xs)-2 else j (take (length xs - 1) xs) Does anyone has a more elegant solution for this first step?