[Haskell-beginners] Structural restrictions in type constructor

[Petr Vápenka]

Maybe not exactly what you need but this was for me a kind of eye-opener
with regard to type system:

https://github.com/leonidas/codeblog/blob/master/2013/2013-02-19-typesafe-tictactoe.md

On Mon, Jun 22, 2015 at 9:09 PM, Rein Henrichs <rein.henrichs at gmail.com>
wrote:

> 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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