expansion of a recursive fibs impl

fibs.hs

scanl f q ls = q : (case ls of
                    []   -> []
                    x:xs -> scanl f (f q x) xs)

fibs = 1 : scanl (+) 1 fibs
       1 : 1 : (case fibs of
                               []   -> []
                               x:xs -> scanl (+) ((+) 1 x) xs)
           # fibs is not []
           # x:xs becomes 1:fibs
           1 : scanl (+) ((+) 1 1) fibs
           1 : scanl (+) 2 fibs
           1 : 2 : (case fibs of
                            []   -> []
                            x:xs -> scanl (+) ((+) 2 x) xs)
               2 : scanl (+) ((+) 2 1) fibs
               2 : scanl (+) 3 fibs
               2 : 3 : (case fibs of
                            []   -> []
                            x:xs -> scanl (+) ((+) 3 x) xs)
                   3 : scanl (+) ((+) 3 2) fibs
                   3 : scanl (+) 5 fibs