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