| Syntactic sugar [message #708951] |
Wed, 03 August 2011 06:06  |
Eclipse User |
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hello,
In the context of the domain model example, the generation of
getters/setters is done twice. The Validator has sources for that (the
new operations are added to the JvmType- Instances), later the code
generator does the same. That's not really code duplication here, but it
seems a little bit odd. Especially if a language has all the syntactic
features to express getters, it seems to me that it would be a better
approach to change the AST (so, insert getters and setters into the AST)
and have no special code for them in Validator and Code Generator.
Especially for languages with a lot of constructs which are to beautify
the syntax only (think of java- style foreach loops, they can easily be
expressed as for- loops or maybe C- style array access where a[5] is the
same as *(a+5), due to the fact that a is a pointer to the first array
element) model-to-model transformation first seems to be a good approach
to simplify code generation.
Is there some hook in xText to do that? So, can I register some model
transformer to be executed before the Validator or at least before the
generator?
(To do something like that before validation could be a problem, because
errors in the transformed parts of the AST can not be reported properly).
Thanks,
Alex
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| Re: Syntactic sugar [message #709273 is a reply to message #709192] |
Wed, 03 August 2011 13:44  |
| Eclipse User |
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Yes, that's right.
What I was looking for is a way to do a model-to-model transformation
BEFORE my code generation starts.
I wasn't talking about type inference or references, but about a way to
perform model-to-model transformation in xText context.
Take the foreach- loop example.
Given a DSL, were (as in Java), those two statements are equivalent:
for(String str:strs){ System.out.println(str); }
and
for(Iterator<String> it=strs.iterator();it.hasNext();){
String str=it.next();
System.out.println(str);
}
so I don't need to write code generation for both constructs. I can
easily write code generation for the second and use model-to-model
transformation to transform all instances of the first example before
code generation. I may even transform them before validation, because
all possible errors in the first example still can be detected in the
second example (the type of strs has no "iterator()"- Method, the
iterator gives no strings, the println- method does not accept "String"
as argument).
Of course I can write some transformer in xTend and call it as first
thing in my generator and my validator as well.
What I am looking for is a build-in mechanism in xText so I don't need
to call it by myself.
Actually: if I call them in my generator and my validator, will they be
executed twice on any AST? Or is the same AST instance passed to
generator and validator?
On 03.08.2011 18:02, Karsten Thoms wrote:
> I think you are mixing type inference and code generation. The domain
> model example generates - as an example - Java bean code, while the Jvm
> model inferer infers types for the concepts of the language in order to
> make them referable within expressions or as targets where type
> references are used. The generator could also produce other kind of
> artifacts, or just do a model-to-model transformation. At the end, it's
> just Java code that does something with a given Model instance. One
> often desired side effect is code generation, where Xtext just adds a
> first-level hook for. What you do in the doGenerate() method is up to
> the implementer.
>
> Kind regards,
> ~Karsten
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