[Haskell-cafe] Re: [Haskell] Recursive definition of fibonacci with Data.Vector

Don Stewart dons at galois.com
Sun Mar 7 15:56:40 EST 2010

> Hello,
> why I can't define a recursive vector using Data.Vector, like in
> the example:
> import qualified Data.Vector as V
> let fib = 0 `V.cons` (1 `V.cons` V.zipWith (+) fib (V.tail v))

There's a typo:

  fib = 0 `V.cons` (1 `V.cons` V.zipWith (+) fib (V.tail fib))

Which let's it typecheck.

But I don't think this is a sensible use of vectors.

In fact, infinite vectors make no sense, as far as I can tell -- these
are fundamentally bounded structures.  GHC even optimizes it to:

    fib = fib


    $ time ./A
    A: <<loop>>

-- Don

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