[antlr-interest] Off topic:Type handling

[Anakreon]

Andrew Deren wrote:
> Just a few comments:
> Why are you doing type analysis in parser for dynamically typed language?
> I've never done anything in asp (or VB), but I've worked on other
> dynamically typed languages and it's almost impossible to do type-checking
> (analysis) at parse (or compile) time. For those language all type
> information is usually only available at runtime.
> For example:
> x = 3
> if (somecondition)
> {
> 	x = "some string";
> }
> 
> // what type is x here?
> z = x;
> 
> There is no way you can now type of x (or z after assignment), because it
> depends on some runtime condition. This is only one of many problems.
> 
> Why are you doing type analysis for VB? Are you trying to compile it or
> translate to typed language?
> 
> Andrew
ASP is translated to PHP which is typeless as well.
But I need the type of variables in certain cases which are demonstrated
in the URL of the mail.
Here is why:
Usefulness of type determination
=================================
1) Currently, if there are more then one method with the same name
   which happens when a method receives variable count arguments,the appropriate
   method is chosen based on the arguments count. This implies the limitation
   that we can not define more then one method in the XML definition with the same
   name and argument count, but with different argument types. This is very useful
   when based on arguments type an other translation exists. We can end with
   wrong translation because of this.
2) The AND, OR, XOR, NOT operators function as binary or logical operators
   based on context. For example a = 12 OR 23 is a binary operator, but currently
   is translated as a logical operator.
3) When functions return arrays, the translator is unaware of this fact. If the
   code requests individual elements of the returned array, an error is produced
   since the translator does not know that the variable holds an array, and an invalid
   translation is generated.
4) When code which falls in the cases (2, 3) exists inside a user defined method
   or sub, and refers to the methods arguments, the same problem appears.
   This problem however is even more difficult to solve because when the method's
   body is translated, the translator can not know the types of the arguments a priori.
   The arguments can be determined only if:
   a) The method is called. Then the types of the arguments passed to the method
	  can be used as the expected types of the arguments. This should be considered
	  as heuristic because a method can be called with different argument types each time.
   b) An operation is performed on an argument which is valid only if the argument
	  belongs to a specific type. ASPA takes an optimistic approach on translation
	  and assumes that the source code to be translated is correct. Because of this
	  we can set the arguments type equal to the one the operation requires. This
	  assumption may not be valid in certain cases hence the translation might be
	  wrong.

Generally is not possible to determine the type of the variable.
There is no why to be always capable of finding the type.
In many cases however it is possible.

I hope someone has faced a similar problem and can make some suggestions on
how to solve the problem.

Anakreon


 
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