[mercury-users] typeclass / collections / unexplainable behaviour

[Jörg Roman Rudnick]

Hi Mark,


it's a great adventure to explore Mercury; to understand more and more and
to gain confidence steadily!

Of course I knew I was going to experiment with daring workarounds, and 
I think
the work you are planning to do will present an even more satisfying 
solution - so,
I guess, it's time for some patience...

If there are some `stupid' tasks to be done for assisting you, I would 
be happy if
you would let me know...

But anyway, I can wait - it is definitely worth the time... ;-)


All the best,

Nick

> As mentioned near the start of section 10.2 of the reference manual,
> the types appearing in instances must be constructors with distinct type
> variables as arguments.  The problem here is that T is not distinct -- it
> appears twice in the arguments of fringeW/2.
>
> We'd really like to lift this restriction, but it's deeply built into the
> implementation and is not likely to be lifted any time soon.
>
> The compiler really should be reporting this error properly.  That's a
> compiler bug (and I'm surprised we haven't noticed this before, since the
> code that is supposed to do this check has been there for a long time).
> We can at least fix the error reporting without too much trouble.
>
> Hope that helps.
>
> Cheers,
> Mark.
>
> -------------------------------------------------------------------------- 
>
> mercury-users mailing list
> Post messages to:       mercury-users at csse.unimelb.edu.au
> Administrative Queries: owner-mercury-users at csse.unimelb.edu.au
> Subscriptions:          mercury-users-request at csse.unimelb.edu.au
> -------------------------------------------------------------------------- 
>
>
>   


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mercurylang.org/archives/users/attachments/20061018/03ec70c3/attachment.html>