[mercury-users] Existential type constraints

[Peter Hawkins]

Mark Brown wrote:

>On 29-Jul-2005, Peter Hawkins <peter at hawkins.emu.id.au> wrote:
>  
>
>>(I just spent an enjoyable 15 minutes tracking down a missing 'some [T]' 
>>on a predicate declaration, and I wasn't helped by a misleading error 
>>message).
>>    
>>
>
>What version of the compiler are you using, and what was the misleading
>error message?
>  
>
$ mmc --version
Mercury Compiler, version rotd-2005-07-07, configured for i686-pc-linux-gnu
Copyright (C) 1993-2005 The University of Melbourne

(self-built)

The error message was like this:
csp_bounds.m:013: In predicate `csp_bounds.propagate/2':
csp_bounds.m:013:   warning: unresolved polymorphism.
csp_bounds.m:013:   The variables with unbound types were:
csp_bounds.m:013:       Var2: ((bdd_solver.cvar).cvar(V_V_1))
csp_bounds.m:013:       Var1: ((bdd_solver.cvar).cvar(V_V_1))
csp_bounds.m:013:       V1: ((bdd_solver.cvar).cvar(V_V_1))
csp_bounds.m:013:   The unbound type variable(s) will be implicitly
csp_bounds.m:013:   bound to the builtin type `void'.
        The body of the clause contains a call to a polymorphic predicate,
        but I can't determine which version should be called,
        because the type variables listed above didn't get bound.
        (I ought to tell you which call caused the problem, but I'm afraid
        you'll have to work it out yourself.  My apologies.)

=)
Peter
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