Subject: Re: another fun one
From: Craig Chambers (chambers@cs.washington.edu)
Date: Mon Apr 09 2001 - 14:45:32 PDT
After thinking about it (but not actually looking at any code), I'm less
convinced that there is not weakness in the typechecker. Vass, can you come by
some time to discuss this with me? Thanks.
-- Craig
Vassily Litvinov wrote:
>
> Upon contemplating on it a bit, I came up with an alternative explanation
> that doesn't involve blaming our greatest-of-all type system and
> the-most-clever-backquote sugar directly.
>
> First, error reporting definitely sucks. To start with, out of six
> constraints reported as "couldn't be solved," one is trivial, three others
> appear as "available," one can be easily derived, and only one is the real
> indicator of the problem. Then, all this "available constraints" business
> at the moment doesn't make sense even to me.
>
> This comes as no surprise, as we are in the classic situation "here's a
> bunch of constraints that cannot be solved. Go find the problem." I
> spent only a very small amount of time on presenting the constraints, but
> non at all on explaining them. Other groups (like recursively-constrained
> types, ESC, Aiken et al.) had to spend a lot of effort producing
> meaningful error messages in a similar situation.
>
> Second, we have no experience with ITC. Likewise someone facing F-bounded
> quantification for the first time can easily get lost. The particular
> kind of error in the includes() implementation is quite common in stdlib
> (I think) and, IMHO, not so difficult to grasp.
>
> BTW I have brief discussions of other typical errors I encountered in
> stdlib a while back in
>
> ~vass/Info/ts-impl-check/LOG-implerrors
>
> I don't know if these are valid arguments; we should definitely try to see
> if we can improve on the type system.
>
> Vass
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