You cannot select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.

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)