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June 22, 2006

New build #292 is out

The new MPS build #292 is out.

I would like to mention one small improvement in this build, which makes the default behavior of the MPS's editor more intelligent.

The default behavior is the set of editing actions that are available just after cells layout for a language concept is defined.
In particular, there is a code-completion action (ctrl-space) which often results in showing of the code-completion menu.

Let's take a look at a local variable declaration (baseLanguage) and code-completion menu for the type of the variable:


From the baseLanguage's structure we know that the variable type should be instance of the Type concept.
View image

Thus, the editor proposes to instantiate the BooleanType (which is successor of the abstract Type concept), IntegerType and other primitives.

But the baseLanguage also defines the ClassifierType which is, in essence, a reference to a Classifier. And what we need is not to merely instantiate ClassifierType but also create a reference to an existing Classifier.
In other words we don't need the ClassifierType in the code-completion menu but names of the classes to choose from.


In the past, such behavior required substantial amount of the customization code to be written. But not any more.

Now the editor is able to automatically detect concepts that are, in fact, merely references, find suitable referent nodes and build auto-completion menu accordingly. Big relief.

Simplistically, the "merely reference" is a concept which declares one reference with multiplicity 1, not abstract and not marked as "doNotSubstituteByDefault".
In addition, this concept shouldn't provide custom matching text to the auto-completion menu.

In our example, the ClassifierType satisfies these conditions.

Let's take another example - the NewExpression concept.
Judging from its structure the NewExpression concept is "merely reference" - it declares one reference with multiplicity 1, not abstract and not marked as "doNotSubstituteByDefault".
But it provides custom matching text (it has alias="new").
View image

So editor doesn't consider it to be "merely reference".
Indeed, an instance of the NewExpression is rendered as new Classname(...).
Thus, the desired sequence of actions is to first choose the "new" from the auto-completion and then choose a constructor.

Returning to the example with the ClassifierType, I've simplified the situation a bit.
Strictly speaking, the concept's structure alone is not enough.
The problem is that in our auto-completion menu we don't want to see *all* classes available in the project.
We are only interested in classes located in the current model and in its imported models.

Such a scope narrowing can be done using model constraints.
I've already blogged about the new constraints language.

Here is how such constraint looks like. It defines search scope for targets of the "classifier" link in the ClassifierType concept.


The "create" function returns an object of type ISearchScope (interface declared in package jetbrains.mps.smodel.search).
Typically, the implementation of ISearchScope is straightforward. It wraps some arbitrary data and implements method

List<SNode> getNodes(Condition<SNode> condition);

which returns a list of nodes satisfying a certain condition.

Posted by Igor Alshannikov at June 22, 2006 08:21 PM


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