Comment 1 Erwan Bousse 2012-04-18 12:02:53 EDT

Created attachment 214193 [details]
The expressions trace, in a separate and readable text file

I'm adding the Expressions "trace" in a separate text file, which is much more readable than my original post.

Comment 2 Erwan Bousse 2012-04-19 09:14:35 EDT

Created attachment 214237 [details]
Test program

Adding a testing program in Java, to explain what I'm concretely trying to do.

Comment 3 Erwan Bousse 2012-04-19 09:17:00 EDT

Created attachment 214238 [details]
Output of Test.java

Adding the output of the test program previously attached.

You can find in this log the "trace" I show in my first post, but also the XMI output of the obtained Alf Block instance (which clearly shows that something is wrong).

Comment 4 Erwan Bousse 2012-04-19 09:32:00 EDT

I finally looked into Alf.xtext, and now I undertand what happens. Here is what we an find in it at some point :

---------------------------

/**************
 * Expressions
 **************/

Expression :
	ConditionalTestExpression
;

ConditionalTestExpression :
	exp=ConditionalOrExpression ('?' whenTrue=ConditionalTestExpression ':' whenFalse=ConditionalTestExpression)?
;

ConditionalOrExpression :
	exp+=ConditionalAndExpression ('||' exp+=ConditionalAndExpression)*
;

ConditionalAndExpression :
	exp+=InclusiveOrExpression ('&&' exp+=InclusiveOrExpression)*
;

InclusiveOrExpression :
	exp+=ExclusiveOrExpression ('|' exp+=ExclusiveOrExpression)*
;

ExclusiveOrExpression :
	exp+=AndExpression ('^' exp+=AndExpression)*
;

// Skipping a lot of lines
// [...]
// Until PrimaryExpression

PrimaryExpression :
	prefix = ValueSpecification 
;
---------------------------


So this is made on purpose : "Expression" rules are expanded one after another. I suppose this is linked to operators priorities, somehow. However, wouldn't it be possible to to something like this instead :


---------------------------
Expression :
	ConditionalTestExpression |
	ConditionalOrExpression |
	ConditionalAndExpression |
	InclusiveOrExpression |
	ExclusiveOrExpression |
	// skipping most Expression rules
	PrimaryExpression 
;
---------------------------


The problem is that the AST we obtain for now is really big... for almost nothing. This will get worse with even bigger Alf programs.



Thanks in advance, and thanks for your work on Papyrus !

Comment 5 Arnaud Cuccuru 2012-04-23 12:22:45 EDT

Hi Erwan,

Indeed, Expression rules in the XText grammar are designed to capture priorities of operators. And as you noticed, this makes ASTs being quite big (for a simple literal, you get an instance of each class in the "hierarchy" of expression rules).

For the moment, there is no plan to make the XText grammar evolve, since any change in the grammar may require significant changes in the validation part of the editor. 

Note however that we are currently working on a transformation from the AST produced by XText to the AST described in the Alf specification (which includes simplifications such as the one you described above with Expressions, but also interesting things such as the construction of the data dependence graph). I will let you know when this is available (hopefully, in the 3rd quarter of 2012).

Comment 6 Erwan Bousse 2012-04-26 03:59:04 EDT

Thank you for your answer !

So there will be two metamodels for Alf : one very close to the concrete syntax, and one based on the spec abstract syntax.

I'll be waiting for this tranformation then :)