20 lines
512 B
Haskell
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)
|