[antlr-interest] Translating expressions - advice?

[Bart Kiers]

I get the impression you think that when creating AST's, ANTLR inserts
parenthesis (brackets). This is not the case: I guess what you're seeing is
just the tree's `toStringTree()` that displays these parenthesis to make the
hierarchy of the tree apparent.
Or am I misinterpreting your question?

Regards,

Bart.



On Mon, May 9, 2011 at 3:10 PM, Hans-Juergen Rennau <hrennau at yahoo.de>wrote:

> Hello People,
>
> being an ANTLR beginner, I would very much appreciate advice concerning
> good
> practise for a rather simple task. The task is the translation of a JPQL's
> (Java
> Persistence Query Language) "where clause" into a proprietary query
> language.
> The clause has the well-known expression structure: operands conncected by
> three
> operators: OR, AND and NOT, where precedence increases in that order.
> Example:
>   a.x='1' AND (a.y='2' OR b.z='3') AND a.v like 'abc%'
>
> An important point is that the translation result will have a similar
> structure,
> that is, it will also be operands connected by those operators. Example:
>   x='1' AND (y='2' OR z='3') AND v='123*'
>
> For this reason I am not sure if the "classical" approach for dealing with
> left-associative operators, as shown in the "Definitve ANTLR Reference" (3.
> A
> quick tour...) is the most appropriate one in this case. I mean rules like:
>   conditional_term ('OR'^ conditional_term)*
>   conditional_factor ('AND'^ conditional_factor)*
>
> This creates deep trees, where each operator creates a new level. That is
> fine
> for processing the operations. But a straightforward translation of the
> tree
> into a similar sequence of operands and operators yields a result which is
> correct but can be ugly, due to superflous brackets, example:
>   (a OR (b OR (c AND d)))
>
> One possibility is to process the tree, removing superfluous brackets -
> perhaps
> by passing the "context operator" into the rule as a parameter, so that the
> rule
> can decide if to create brackets or not. This should not be too difficult,
> but
> my question is: is there a good practise for accomplishing the task? Would
> you
> recommend the approach just sketched, or a different tree representation to
> start with?
>
> (A tree I do want because there are other parts to be translated, not only
> the
> where clause, and a tree seems to me the way to deal with (possibly yet
> growing)
> complexity.
>
> Thank you very much for any suggestions.
>
> -- Hans-Juergen
>
>
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