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-- Several versions of Fibonacci
--------------------


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-- Standard recursive version (slow!)

fibr 0 = 0
fibr 1 = 1
fibr n = fibr (n-1) + fibr (n-2)


--------------------
-- Accumulating parameter version

fiba n = fib 0 1 n
         where fib p q 0 = p
               fib p q 1 = q
               fib p q n = fib q (p+q) (n-1)


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-- Zipped list version (using a LOCAL definition)

fibl n = fibs !! n
         where fibs = 0 : 1 : zipWith (+) fibs (tail fibs)


--------------------
-- Zipped list version (using a GLOBAL definition)

fibl' n = fibs' !! n
fibs' = 0 : 1 : zipWith (+) fibs' (tail fibs')



--------------------
-- Some sample values for testing timing results

j = fibl' 100

k = fibl' 100

ys = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30]

y  = ys !! 29