Subject: Re: impl typechecking errors
From: Craig Chambers (chambers@cs.washington.edu)
Date: Fri Apr 06 2001 - 19:39:58 PDT
OK, I'll chalk this one up to a convoluted subtyping/inheritance design.
(Several of those in the stdlib I've identified so far....)
-- Craig
Vassily Litvinov wrote:
>
> This message is tough to decipher, and I don't have a general recipe apart
> from complaining to me. You may want to set the Vortex option "tc_debug"
> to true to get a more meaningful error message, but even that wouldn't
> help in this case.
>
> Turns out that this is a *real* ITC error - which I didn't realize until
> after I had written an almost complete apology for my constraint solver
> being imperfect and in need of fixing.
>
> The reason is that triple subtypes pair. As a result, for triple[T1,T2,T3]
> to be hashable (and send of hash(triple[..],int) to be legal, according to
> the signature), it suffices that the corresponding pair[T1,T2] be hashable.
> As a result, send of hash(triple[T1,T2,T3],int) is legal if T1 and T2 are
> hashable, but not necessarily T3. The method implementation for this send
> naturally expects T3 to be hashable as well. Hence the error.
>
> For a similar reason it is legal to compare (using <=) a triple and a
> quadruple (given appropriate type params), which (I guess) shouldn't be
> the case.
>
> The right solution, of course, is to make triple a *private* subtype of
> pair. (And of course first figure out what "private subtyping" should
> mean.) Meanwhile there needs to be some workaround.....
>
> Vass
>
> PS. This lets me insert a plug for Vortex browser features. Typing in:
>
> Vortex> subtypes triple 3 hashable 1
>
> gives all the ways for a triple to subtype a hashable. You still may have
> to contemplate the output to figure out what's going on...
>
> On Thu, 5 Apr 2001, Craig Chambers wrote:
>
> > I got the following weird itc error:
> >
> > comparable.cecil:143: implementation type error
> > Kind: could not find legal instantiation of the callee
> > Sig: signature hash(hashable[`T], range:int):int
> > Recvs: -triple[A,B,C], *-
> > Callee: method hash(p@:triple[`T1 <= hashable[T1], `T2 <= hashable[T2], `T3 <=
> > hashable[T3]], range:int):int
> > Instantiated signature:
> > signature hash(hashable[`T], range:int):int
> > Instantiated receivers:
> > -triple[`#T1-2,`#T2-2,`#T3-2], *-
> > Available constraints:
> > SUB `#T-1 <= hashable[`#T-1]
> > SUB `#T-1 <= pair[`#T2-3,`#T3-3]
> > SUB `#T1-2 <= hashable[`#T2-3]
> > SUB `#T2-2 <= hashable[`#T3-3]
> > SUB `#T1-2 <= `#T2-3
> > SUB `#T2-3 <= hashable[`#T2-3]
> > SUB `#T2-2 <= `#T3-3
> > SUB `#T3-3 <= hashable[`#T3-3]
> > Callee instantiation constraints - could not solve them:
> > hash(p@:triple[`T1 <= hashable[T1], `T2 <= hashable[T2], `T3 <= hashable[T3]],
> > range:int):int
> > hash(p@:triple[`T1 <= hashable[T1], `T2 <= hashable[T2], `T3 <= hashable[T3]],
> > range:int):int
> > hash(p@:triple[`T1 <= hashable[T1], `T2 <= hashable[T2], `T3 <= hashable[T3]],
> > range:int):int
> > SUB triple[`#T1-2,`#T2-2,`#T3-2] <= triple[`#T1-2,`#T2-2,`#T3-2]
> > SUB int <= int
> > SUB int <= int
> >
> > Vass, can you explain what the problem is with sending hash to a triple of
> > hashables?
> >
> > -- Craig
> >
_______________________________________________
Cecil mailing list
Cecil@cs.washington.edu
http://majordomo.cs.washington.edu/mailman/listinfo/cecil
This archive was generated by hypermail 2b25 : Fri Apr 06 2001 - 19:40:03 PDT