[stringtemplate-interest] Changing separators in recursive templates

[Terence Parr]

On Aug 14, 2008, at 10:36 AM, asword at telus.net wrote:

> Hello,
>
>  I recently started using StringTemplate, and haven't found my  
> around all the docs and mailing lists yet.  I am using the C#  
> version 3.1beta (since it adds features I need).  I've run into a  
> few problems here and there, particularly with trying to use  
> recursive templates.  The latest one seemed like a flat out bug so I  
> thought I would inquire about it.
>  The situation is that I have a graph of objects that represent a C+ 
> + boolean expression that I want to output.  My initial attempt at  
> this was roughly this (I don't have the original code as I've worked  
> around the problem by taking a different strategy, I would just like  
> to know why it didn't work):
>  BinaryOp(node, op) ::=  
> "$node.SubExpressions:EvalElement(elem=it);separator=op$"
> EvalElement(elem) ::= <<
>
> $if(elem.IsBinaryOp)$
>
> ($BinaryOp(node=elem,op=node.Op)$)
>
> $else$
>
> $elem.Condition$
>
> $endif$
>
> >>
>
>
> This almost worked.  The problem arose when it had recursed a level  
> or two and the op changed from (for example) "&&" to "||" and back  
> again.  The "||" never appeared, instead the separator was always  
> "&&" at all levels.
>

That does seem strange.  Perhaps you could simply do separator=node.Op  
to avoid Anything weird with the parameters.

> Also, are there any hints to debugging templates more effectively?   
> I'm finding that it is mostly guesswork and that I get NoViableAlt  
> exceptions which don't provide any clues as to their source.  Many  
> of these are caught internally by StringTemplate, and if I have the  
> debugger set to stop at the exception then I have to step through  
> potentially dozens of them until I get to the exception that I  
> really want to look at.
>

NoViable alt errors are parse errors...often the line numbers are not  
exactly helpful because the errors are within an action. I'm not  
familiar enough with C# implementation to know what the real issues are.

Ter