# Understanding Haskell's fibonacci

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by AR
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Published on 2010-03-08T19:37:55Z
Indexed on
2010/03/09
1:21 UTC

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```
fibs :: [Int]
fibs = 0 : 1 : [ a + b | (a, b) <- zip fibs (tail fibs)]
```

This generates the Fibonacci sequence.

I understand the behaviour of the guards, of `:`

, `zip`

and `tail`

, but I don't understand `<-`

. What is it doing here?

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