[stringtemplate-interest] separator: a fix or breaking backward compatibility?

[Terence Parr]

On Jul 6, 2009, at 6:44 PM, Sterling Clover wrote:

> I think I'm late to the party here, but I really dislike this  
> change. The functionality you describe is indeed mostly missing  
> without it, but the change feels semantically hackish. It feels  
> cleaner to reason about a language where a template *always*  
> produces a value than one where a template optionally produces one.  
> For example, this is what you describe:
>
> <names:{n | <if(n.cool)><n><endif>}; separator=",">
>
> But what about this (note the extra whitespace):
>
> <names:{n |  <if(n.cool)><n><endif>}; separator=",">
>
> To have the two behave so differently seems very unintuitive.

Hi :)  Well, i do say in the manual that i consume all whitespace  
after the '|' char.

> What I think you really want is something closer to standard list  
> comprehension syntax, where a list is filtered on a condition. Since  
> this provides the same power as what you've got below, I don't think  
> it would hurt the logic/view split that stringtemplate enforces, and  
> it would make templates more concise and readable. Now as to what  
> the syntax is, that's a different issue. Something like the  
> following, perhaps?
>
> <names:{n: n.cool | n}; separator=",">
>
> The problem here is of course the colon is somewhat unintuitive, but  
> the standard set builder symbol for "such that" is the vertical bar,  
> which is already taken. Other suggestions, all equally not ideal,  
> follow:
>
> <names:{n st. n.cool | n}; separator=",">
> <names:{n & n.cool | n}; separator=",">
> <names:{n when n.cool | n}; separator=",">
> <names:{n where n.cool | n}; separator=",">
> <names:{n % n.cool | n}; separator=",">
> <names:{n ^ n.cool | n}; separator=",">
>
> You get the idea.

Yep. it's a good idea.  The problem is that you might get multiple IF  
in a row that are "nullable".  Or, you could ref an attribute that is  
a list with no elements.

<foo : { f | <n>}; separator=", ">

if foo is List<List<string>> and one of the List<string> is length 0,  
you'd want to avoid the extra separator, right?

Thanks,
Ter