[Haskell-cafe] Finite but not fixed length...

[Jonas Almström Duregård]

...and you can always do

hack :: Vec n a -> FixedVec a
hack x :: FixedVec undefined

Also I'm guessing 1, 2 and 17 are just examples, he really wants arbitrary
length finite lists.

/J

On 13 October 2010 20:47, Daniel Peebles <pumpkingod at gmail.com> wrote:

> One option could be something like:
>
> data Z
> data S n
>
> data Vec n a where
>   Nil :: Vec Z a
>   Cons :: a -> Vec n a -> Vec (S n) a
>
> data Length n where
>   One :: Length (S Z)
>   Two :: Length (S (S Z))
>   Seventeen :: Length (S (S (S (S (S (S (S (S (S (S (S (S (S (S (S (S (S
> Z)))))))))))))))))
>
> data FixedVec a where
>   FixedVec :: Legnth n -> Vec n a -> FixedVec a
>
> But it's obviously rather cumbersome :)
>
>
> On Wed, Oct 13, 2010 at 7:57 AM, Jason Dusek <jason.dusek at gmail.com>wrote:
>
>>  Is there a way to write a Haskell data structure that is
>>  necessarily only one or two or seventeen items long; but
>>  that is nonetheless statically guaranteed to be of finite
>>  length?
>>
>> --
>> Jason Dusek
>> Linux User #510144 | http://counter.li.org/
>> _______________________________________________
>> Haskell-Cafe mailing list
>> Haskell-Cafe at haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>
>
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