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Haskell Cookbook by Yogesh Sajanikar

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Working with recursive functions

In this recipe, we will calculate fibonacci numbers by writing a simple recursive function. Fibonacci numbers are the numbers appearing in the fibonacci sequence.

Fibonacci numbers are calculated as follows:

Fn = Fn-1 + Fn-2

We need to provide the first two seed fibonacci numbers in the sequence so that we can calculate the next set of fibonacci numbers. We will seed the sequence with 0 and 1. Our sequence will look like this:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144 ....

We will start indexing with 0. Hence, the 0th fibonacci number is 0, 1st fibonacci number is 1, .. 5th fibonacci number is 5 ... and so on.

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