discuss.visual-prolog.com

Posted: **8 Aug 2014 15:21**

Hi Thomas,

the compiler build 7500 throws error c520 : Impossible to determine the type of the term on this code. I suppose, it is not intended:

Code: Select all

interface myObj{@Type}
    domains
        useTheParameter = @Type.
end interface myObj
 
class myObj{@Type} : myObj{@Type}
end class myObj
 
implement myObj{@Type}
end implement myObj
 
implement main
    clauses
        run() :-
            _ = myObj{integer}::new.
end implement main

Regards,
Martin

Posted: **8 Aug 2014 16:03**

parenthesis:

run() :-
_ = myObj{integer}::new().

Posted: **8 Aug 2014 17:24**

Hello Markov,

appending the parenthesis is not compellent. myObj{integer}::new is a legal expression. It has the type () -> myObj{integer}, i.e. a function type.

Regards,
Martin

Posted: **9 Aug 2014 5:43**

Hello Meyer!
You try:

run() :-
_ = myObj{integer}::new().

It is a good tablet

Posted: **9 Aug 2014 11:27**

The type checker is only supposed to say "impossible to determine the type" if something remains polymorphic, i.e. if one of the types can be chosen arbitrarily and still solve the system.

That would have been the case it you had written:

Code: Select all

clauses
    run() :- 
        _ = myObj::new.

But when instantiating the class with integer, only integer will solve the system. So this is a bug.

The situation will however not happen often, because normally you will use the value (rather than just throwing it away like here), and then the usage will typically fix the type:

Code: Select all

clauses
    run() :-
       Factory = myObj::new,
       use(Factory).

Should nothing fix the type, you can fix it explicitly using hasDomain:

Code: Select all

clauses
    run() :-
       hasDomain(core::function{integer}, Factory),
       Factory = myObj::new,
       use(Factory).

Or using the new (i.e. vip 7.5) function form of hasDomain:

Code: Select all

clauses
    run() :-
       Factory = hasDomain(core::function{integer}, myObj::new),
       use(Factory).

We will of course address the bug.

Posted: **9 Aug 2014 12:02**

Thanx Thomas and VITALY (I guess, by "Hello Meyer" you are giving me a wink, that Vitaly is your first name

)!

Best Regards,
Martin

discuss.visual-prolog.com

Constructor's type not determined

Constructor's type not determined