[Haskell-beginners] Structural restrictions in type constructor

[Rein Henrichs]

You can't do this at the type level in Haskell.

On Mon, Jun 22, 2015 at 7:00 AM Matt Williams <matt.williams45.mw at gmail.com>
wrote:

> OK, I think this is clearly well beyond my level!
>
> Will insert some manual checking.
>
> Thanks,
> Matt
>
> On 22 June 2015 at 14:51, emacstheviking <objitsu at gmail.com> wrote:
>
>> It *could* be done and might already have been done... I seem to recall a
>> few months back somebody asked for a similar feature using one of the
>> vector libraries, to limit one of the input vectors to a fixed length?
>>
>> You'd have to dig through the list archives though...
>>
>> On 22 June 2015 at 12:36, Imants Cekusins <imantc at gmail.com> wrote:
>>
>>> > But this is checking the values in the implementation, not a type level
>>> build time guarantee, isn't it?
>>>
>>> yep, correct. Could be caught by unit tests though :-P
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