Compiling error

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jeangil
Posts: 10
Joined: 8 Sep 2019 15:59

Compiling error

Unread post by jeangil » 13 Oct 2019 18:50

Hello,

I try to compile a List and Recursion in Wiki example (see code below),
And I got a compiling error:

" e221 several classes interfaces and/or namespaces have the same name "main""

I don't understand why ? I try to change the name of the class but it gave more compiling errors !

Thaks for helping me ?

Regards :D

jeangil

Code: Select all

class main    predicates     length_of : (A* List, integer Counter) -> integer Result.    end class    implement main    clauses     length_of([], Counter) = Counter.     length_of([_ | T], Counter) = Result :-         NewCounter = Counter + 1,         Result = length_of(T, NewCounter).    end implement main   goal     console::init(),     main::length_of([1, 2, 3], L, 0), /* start with Counter = 0 */     stdio::write(" L = ", L).

Martin Meyer
VIP Member
Posts: 289
Joined: 14 Nov 2002 0:01

Re: Compiling error

Unread post by Martin Meyer » 13 Oct 2019 21:23

The reason of error several classes interfaces and/or namespaces have the same name "main" is that 'empty' projects already contain a class main and you have created a second class having the same name. Class names must be unique however (in each namespace).

I think there are two issues about the example Tail Recursion:

1st) It is written in an earlier version of Visual Prolog. In the current Visual Prolog 9 the intended place, where to insert your code, is different. When we create a new console style project in current VIP, main.cl will be:

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% Copyright   class main     open core   predicates     run : core::runnable.   end class main
and main.pro is

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% Copyright   implement main     open core   clauses     run() :-         CP = commandLineParser::new(),         CP:acceptEmpty := true,         CP:addOption_help("-help"),         % define command line options here         if ErrorMessage = isSome(CP:parse()) then             stdio::write(ErrorMessage)         else             % place your own code here         end if.   end implement main   goal     console::runUtf8(main::run).
Provided you do not need/want the commandLineParser stuff, you can clean them up a little, so that they become:

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class main   predicates     run : core::runnable.   end class main
and

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implement main   clauses     run() :-             % place your own code here   end implement main   goal     console::runUtf8(main::run).
Now (and always) leave the goal as it is. Just replace the % place your own code here by your main code. That is in case of the old wiki-example the lines from the goal. Ommit but the line console::init(),. This line was good only in an earlier VIP version. Thereafter main.pro looks:

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implement main   clauses     run() :-         main::length_of([1, 2, 3], L, 0), /* start with Counter = 0 */         stdio::write(" L = ", L).   end implement main   goal     console::runUtf8(main::run).
Complete setting up the example by inserting the declaration und clauses of predicate length_of/2->. Done that, main.cl and main.pro are:

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class main   predicates     length_of : (A* List, integer Counter) -> integer Result.   predicates     run : core::runnable.   end class main

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implement main   clauses     length_of([], Counter) = Counter.     length_of([_ | T], Counter) = Result :-         NewCounter = Counter + 1,         Result = length_of(T, NewCounter).   clauses     run() :-         main::length_of([1, 2, 3], L, 0), /* start with Counter = 0 */         stdio::write(" L = ", L).   end implement main   goal     console::runUtf8(main::run).
When you now compile resp. build the project, then

2nd) issue pops up: Undeclared identifier 'main::length_of/3', the identifier is known as 'length_of/2->' in the class 'main'. The compiler complains because the call main::length_of([1, 2, 3], L, 0) does not fit to the declaration of predicate length_of/2->.

Having corrected the wrong call and furthermore removing a superflous qualification main:: the implementation eventually becomes:

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implement main   clauses     length_of([], Counter) = Counter.     length_of([_ | T], Counter) = Result :-         NewCounter = Counter + 1,         Result = length_of(T, NewCounter).   clauses     run() :-         L = length_of([1, 2, 3], 0), /* start with Counter = 0 */         stdio::write(" L = ", L).   end implement main   goal     console::runUtf8(main::run).
Now the example works fine. :D

It can however be coded a bit shorter:

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implement main   clauses     length_of([], Counter) = Counter.     length_of([_ | T], Counter) = length_of(T, Counter + 1).   clauses     run() :-         L = length_of([1, 2, 3], 0), /* start with Counter = 0 */         stdio::write(" L = ", L).   end implement main   goal     console::runUtf8(main::run).
Regards Martin

jeangil
Posts: 10
Joined: 8 Sep 2019 15:59

Re: Compiling error

Unread post by jeangil » 14 Oct 2019 20:46

Thanks a lot for your reply,
I will try this tomorow,

Thanks again.

Regards

JeanGil

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