[Laszlo-dev] Constraint function generator

[P T Withington]

On 2008-02-19, at 19:00 EST, Donald Anderson wrote:

> Henry,
>
> I have the constraint function generator mostly ready.
>
> First question - do we need an option to compute meta references?
> That's apparently a compile time option, but I don't see when it's  
> turned on.

That was a failed experiment.  Correct, but determined to be too  
slow.  For now, we are just keeping the code as a reference  
implementation, turned off.  It is trying to solve the problem that if  
a constraint says `a.b.c`, we only listen for `c` changing in `a.b`;  
if `b` changes in `a`, we won't notice.

> In my current version, I am accepting as arguments 1) the name of  
> the original function,
> and 2) the source for the function, for the moment I expect the source
> to look just like what you are now generating.
>
> I am returning the source of a function with the name  
> XXX_dependencies.

I agree with you and Henry that it will be more useful going forward  
if you accept an arbitrary expression (as a string) and return the  
expression that computes the dependencies for that (also as a  
string).  Thus, to retrofit your code to the current "pattern" you  
would analyze the expression that is the second argument to  
setAttribute in the current constraint functions.

Are you doing this in RingDing?  I think that would be the best place,  
since then we can test against the known-working test cases.

> For example, input source is this: (culled from where this string is  
> made in NodeModel.java):
>
> ===
> function $base$2Fbasefocusview$2Elzx_282_41_x_always () {
> #pragma 'constraintFunction'
>
> #pragma 'withThis'
> this.setAttribute("x",
> #beginAttribute
>
> #file base/basefocusview.lzx
> #line 282
>                                         -classroot.offset
> #endAttribute
> )}
> ===
>
> Output source is currently:
>
> ===
> /* -*- file: Compiler.substitute#-1.1 -*- */
> function $base$2Fbasefocusview$2Elzx_282_41_x_always_dependencies () {
> #pragma "warnUndefinedReferences=false";
> with (this) {
> return [classroot, "offset"]
> }}
> ===
>
> I'm thinking instead I could accept simply '-classroot.offset'
> and return just the text of the statements:
>  with (this) {
>    return [classroot, "offset"]
> }

I would leave out the `with (this)` and have that be an implicit  
burden on the callee.  (Especially because that is implicit in JS2  
method bodies).

> Then you could name the function whatever you want or
> use it as a function expression.  Or I could return just the
> array (as an expression) like '[classroot, "offset"]' .  It depends
> on how you plan to use it,  vs. how much of the details you need to  
> know.
>
> - Don
>
> --
>
> Don Anderson
> Java/C/C++, Berkeley DB, systems consultant
>
> voice: 617-547-7881
> email: dda at ddanderson.com
> www: http://www.ddanderson.com
>
>
>
>