[mercury-users] constrained polymorphic mode error

[Fergus Henderson]

On 09-Aug-2002, Tom Schrijvers <Tom.Schrijvers at cs.kuleuven.ac.be> wrote:
> Here is another error that puzzles me:
> 
> $ mmc cpm_error.m -E
> cpm_error.m:031: In clause for `m(in(cpm_error:val_closure(cpm_error:closure_list((X =< ground)))), out(cpm_error:closure_list((X =< ground))))':
> cpm_error.m:031:   in argument 1 of call to predicate `cpm_error:eval/2':
> cpm_error.m:031:   mode error: variable `CCL' has instantiatedness `cpm_error:val_closure(cpm_error:closure_list((X =< ground)))',
> cpm_error.m:031:   expected instantiatedness was `cpm_error:val_closure((V_2 =< ground))'.
> 
> $ mmc -v
> Mercury Compiler, version rotd-2002-08-05, configured for i686-pc-linux-gnu
> 
> As far as I can tell it holds that
> 
>   cpm_error:closure_list((X =< ground)) =< ground
> 
> so why does the compiler generate this error?

That one looks to me at first glance like a compiler bug.
When I tried to simplify the test case, the compiler threw up its hands
("Uncaught Mercury exception: Software Error: ... unify_inst failed"),
which indicates that it is definitely a bit confused about these constructs.

Thanks for reporting this -- we will look into it and see if we can
come up with a fix.

Note that this is a fairly new feature, which is not included in the
latest stable release, so I guess it is not *too* suprising that it
may have some bugs.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
The University of Melbourne         |  of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh>  |     -- the last words of T. S. Garp.
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