6 lines
184 B
FSharp
6 lines
184 B
FSharp
let fib = function
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| n when n < 0 -> None
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| n -> let rec fib2 = function
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| 0 | 1 -> 1
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| n -> fib2 (n-1) + fib2 (n-2)
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in Some (fib2 n)
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