Henrique Dias 0afb9e732c update
Former-commit-id: bdede6ed1b6f578f2ef046c338caf02d0b29d453 [formerly 7187de361b53e9c8ec121df379b762f2db736ea2]
Former-commit-id: 447d58460fbbfd05ffe08428a1288e392637561d
2017-03-25 19:37:42 +00:00

20 lines
512 B
Haskell

-- Type annotation (optional)
fib :: Int -> Integer
-- With self-referencing data
fib n = fibs !! n
where fibs = 0 : scanl (+) 1 fibs
-- 0,1,1,2,3,5,...
-- Same, coded directly
fib n = fibs !! n
where fibs = 0 : 1 : next fibs
next (a : t@(b:_)) = (a+b) : next t
-- Similar idea, using zipWith
fib n = fibs !! n
where fibs = 0 : 1 : zipWith (+) fibs (tail fibs)
-- Using a generator function
fib n = fibs (0,1) !! n
where fibs (a,b) = a : fibs (b,a+b)