Re: [Adobe-source-devel] Questions about conditional_indirect_contributing_m

[Sean P. <sea...@ma...>]

Hi cee1,

Release 42 was a bit rushed and there are a couple of bugs in the adam  
code - the current mainline should be in could shape. I'm going to use  
that code for this discussion - you can see it here:

http://stlab.adobe.com:8080/@lno=y@//adobe_source_libraries/source/adam.cpp?ac=64&rev1=23

On Feb 13, 2010, at 3:21 AM, cee1 wrote:

> Hi all,
> I'm reading the code of asl 1.0.42.
> Some questions about conditional_indirect_contributing_m:
> I found "conditional_indirect_contributing_m" (data member of  
> sheet_t::implementation_t) is only set in function  
> sheet_t::implementation_t::update:
> (adam.cpp, 1119) accumulate_contributing_m.reset ();

Adjusting line numbers:

  1162.	    accumulate_contributing_m.reset();
> ...
> (adam.cpp, 1143) conditional_indirect_contributing_m =  
> accumulate_contributing_m;

And:

  1186.	    conditional_indirect_contributing_m =  
accumulate_contributing_m;

>
> It seems conditional_indirect_contributing_m will always be zero,  
> and is referenced as "a_variable |=  
> conditional_indirect_contributing_m", should it be useless? What is  
> conditional_indirect_contributing_m doing?


No - accumulate_contributing_m is a member variable and will  
accumulate bits (denoting cells) as variables are looked up when a  
cell expression is evaluated (variable lookup is bound to  
sheet_t::get()). Same discussion as on this prior thread <http://sourceforge.net/mailarchive/forum.php?thread_name=999EDB9A-2AFD-4E03-B3BA-97C1193FB8F1%40mac.com&forum_name=adobe-source-devel 
 >.

> What is conditional_indirect_contributing_m doing?


A relation can be conditional using a when() clause:

when (p) relate {
	x <== y;
	y <== x;
}

The conditional predicates are evaluated prior to flowing the  
relationships. conditional_indirect_contributing_m is an accumulation  
of all cells contributing to the conditional predicates. These  
indirectly contribute to any cell which is in calculated after.

>
> BTW, I've read the introduction at http://stlab.adobe.com and the  
> paper "Property Models -- From Incidental Algorithms to Reusable  
> Components", I'm still confused about:
> What is the difference between output and interface cells?
The implementation of interface cells is a pair of cells,  
interface_input and interface_output. An interface cell (and only an  
interface cell) can be involved in a relate clause and  for any state  
in the system either the input half is contributing or the output half  
is derived (or both if there is a self-reference loop).

> Data flow of various cells? (e.g. data from input cell only flow to  
> output|interface cell? output|interface cell only accept data from  
> input cell?)

See slide 66 here <http://stlab.adobe.com/wiki/images/0/00/2008_04_03_accu.pdf 
 >

> What is the difference between input and interface cells(e.g. why  
> input cell setting init_contributing_m while interface cell(input)  
> setting contributing_m)?

Interface cells are used to seed the sheet during initialization. We  
track the contributing values during initialization because a sheet  
can be "re-initialized" (this would happen if the state of something  
the sheet relies on was updated outside of the sheet). An input cell's  
value can only be set from code external to the sheet, where as the  
value in an interface cell (input side) can be applied from the output  
side fo the same cell. You can only bind an interface cell to  
something like an edit text widget because the input side can be set  
(controller side of widget) and the output side is displayed (view  
side of widget).

> Are relation cells only involved in "getting" value of interface  
> cells (output)?
A relation cell holds the bundle of expressions that binds the input  
side of the interface cell to the output side of the interface cell,  
along with any conditional predicates.

> What is invariant cell doing? If an invariant cell evaluated  
> "false", all cells contributing to it will be marked poison?
Correct, and then any cell derived from poison is marked as invalid.  
Consider a simple form where you must specify an age and the age must  
not be less than 21.

sheet drinking_test {
   interface:
     age : 0;
   invariant:
    age_test <==  !(age < 21);
   output:
    result <== age;
}

A layout to bind to this might look like:

layout drinking_test {
	view dialog() {
		edit_number(name: "Age", bind: @age);
		button(name: "Drink!", bind: @result);
	}
}

Here if age < 21 then age_test is false so age is marked as poison,  
result is derived from age so it is marked as invalid. The Drink!  
button, which is bound to result, will use the invalid flag to control  
enablement and will be disabled (a button invokes some function, and  
the value it is bound to is the arguments to that function, so if the  
arguments are invalid, then the pre-conditions of the function are not  
satisfied, and the button is disabled).

Hope that help,
Sean


>
> Regards
> -- cee1
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