presenter::mkExpand

[Martin Meyer]

Hello Thomas,

when setting a breakpoint in below code at the indicated line and running it in the debugger (in build 902), a line for variable Num is displayed in the "Variables in the Current Clause" window. However (with "Native View" not checked on) the line cannot be expanded by mouse click. I suppose that is not intended?

Code: Select all

domains
    num = unsigned [presenter(present_num)].
 
class predicates
    getNumName : (num) -> string.
clauses
    getNumName(0) = "zero" :-
        !.
    getNumName(1) = "one" :-
        !.
    getNumName(_) = "many".
 
class predicates
    present_num : presenter::presenter{num}.
clauses
    present_num(Num) = present_num(Num, Num).
 
class predicates
    present_num : (num Num, unsigned NumUnsigned) -> presenter::presentation.
clauses
    present_num(Num, NumUnsigned) = presenter::mkExpand(Name, NumUnsigned) :-
        Name = getNumName(Num).
 
class predicates
    test : (num).
clauses
    test(Num) :-
        stdIO::write(Num).  %set a breakpoint here
 
clauses
    run() :-
        test(1).

[Thomas Linder Puls]

No, that is a bug.

By the way, (it will not solve the bug, but) you can write your presenter like this:

Code: Select all

class predicates
    present_num : presenter::presenter{num}.
clauses
    present_num(Num) = presenter::mkExpand(getNumName(Num), hasDomain(unsigned, Num)).

[Thomas Linder Puls]

I am sorry I was confused when I answered before. An "expand" presentation will be presented as its first argument, and expand as the second term. But an unsigned doesn't expand, so this presentation will not expand.

In your case you should use a fixed presentation with a string and a "child only" component:

Code: Select all

class predicates
    present_num : presenter::presenter{num}.
clauses
    present_num(Num) =
        presenter::mkPresenter_fixed(
            presenter::fp_string(getNumName(Num)), 
            presenter::mkFP_childOnly_term("Value", hasDomain(unsigned, Num))).

Which will give this

num_presenter.png (5.25 KiB) Viewed 884 times

[Martin Meyer]

Ahhh OK, I got it. And reading the wiki more carefully I see that is also documented well. Thank you!

[Martin Meyer]

But why does below wrapper object not expand (in non-native view)?

Code: Select all

interface obj
    [presenter]
end interface obj
 
class obj : obj
end class obj
 
implement obj
    open presenter
 
clauses
    presenter() = mkPresenter_fixed(
        fp_string("I am an obj"), 
        presenter::mkFP_childOnly_term("I am the expansion of an obj", compiler_version)).
 
end implement obj
 
%===
 
interface wrapper
    [presenter]
end interface wrapper
 
class wrapper : wrapper
 
constructors
    new : (obj).
 
end class wrapper
 
implement wrapper
    open presenter
 
facts
    obj : obj.
 
clauses
    new(Obj) :-
        obj := Obj.
 
clauses
    presenter() = mkExpand("I am a wrapper", obj).
 
end implement wrapper
 
%===
 
implement main
 
clauses
    run() :-
        Obj = obj::new(),
        Wrapper = wrapper::new(Obj),
        stdIO::write(Wrapper, ", ", Obj).  %set a breakpoint here
 
end implement main

[Thomas Linder Puls]

Yes, that it is a good question . We will look at it.

[Thomas Linder Puls]

My brain has looked into some forgotten memory slots (or invented a story).

Though this is not what consistent with the documentation, I think this is deliberate. What happens is that a an "expand" presentation, will show/write the first argument, but expand like the native expansion of the second argument.

The reason for using the native expansion of the second argument is exactly the object case, where you want a nice string-presentation, but a straight forward expansion with all the facts, etc.

[Thomas Linder Puls]

My colleagues agree it is the native expansion that is used. I have added the word to the documentation.

[Martin Meyer]

Yes, it's all consistent now. Thank you.