[stringtemplate-interest] [ST4] How to avoid map key iteration?

[Terence Parr]

Everything we add to the language has a cost, which includes new syntax and semantics.

To me, it's simple--the ':' operator means apply a template or templates across a value or multiple values. The left-hand side of ':' is always serialized. If you do not wish it to be serialized, don't use the ':' on that object.  You are basically trying to use it to simply get a new name:

<amap:{x | <x.field>}>

but you should simply use this instead:

<amap.field>

I explored the notion of no () on template mapping; as you point out we should be passing the template name not making a template instantiation. It turns out I decided I like highlighting the fact that it was a template application.

I've generated a lot of structured text with ST over the years from websites to bytecodes to Java. I've never found this to be an issue;  at least from my perspective, there's nothing to fix.

Ter

On Feb 14, 2011, at 8:01 AM, Udo Borkowski wrote:

> Hi Sam,
> 
> your suggestion of using a syntax like "line2(adr)" to invoke an anonymous template goes exactly in a direction I was thinking for a while now: 
> 
> (Start of dreams of the future)
> 
> The "Unified ST4 template" syntax 
> 
> Currently we defined "normal" templates like
> 
>     t1(p1,p2) ::= <<…>> 
> 
> or 
> 
>     t1(p1,p2) ::= "…"
> 
> Anonymous templates (or sub templates) are defines like 
> 
>     {p1,p2| …}.
> 
> 
> What about defining a "normal" template like this:
> 
>     t1 = {p1,p2| …}
> 
> I.e. a "normal" template is just an anonymous template with a name, i.e. the template can be referenced through this name.
> 
> To invoke a template use the same syntax as before:  
> 
>     <t1(x,y)>
> 
> However one can also just *reference* a template (without invoking it), just by naming it without the (...).
> 
> The "iterate" feature would work on a (named or anonymous) template (as now), but would get a slightly different syntax for named templates:
> 
>     <x,y:t1>     
> 
> I.e. no "t1()" as with a template invocation, but just "t1" to reference the template. This perfectly fits into the "<x,y:{…}>" syntax: here the "{…}" is not written as "{…}()", too.
> 
> This changed syntax also makes the difference between a normal template call:
> 
> 	<t2()>
> 
> and the iterate feature:
> 
> 	<x,y:t1>
> 
> a little bit more obvious. (Another way to see this: the () behind the template name in an iterate feature serve no real purpose, they will always be empty).
> 
> To come back to my initial question "how to avoid map key iteration" I could imagine an extension to the "iterate" syntax:
> 
> Either
> 
> 	<x*,y:t1>
> 
> Meaning: only the x parameter is used as an iterator, the other parameters are just passed to the template unchanged.
> 
> Or
> 
> 	<x,y!:t1>
> 
> Meaning: every parameter not marked with "!" is used as an iterator.
> 
> ( '*' and '!' are just used as examples. Use your favorite syntax here to mark a parameter either as "iterator" or as "pure value").
> 
> 
> (End of dreams of the future)
> 
> 
> Udo
> 
> 
> On 14.02.2011, at 15:35, Sam Harwell wrote:
> 
>> Hi Udo,
>>  
>> The problem is the operation in use when you write it the way you originally did – the ‘:’ is a map operation as opposed to a pass to a function method. In theory, the following syntax could solve the problem:
>>  
>> t2(adr,line2={x|<x.zip> <x.city>}) ::= <<
>> <adr.firstname> <adr.lastname>
>> <line2(adr)>
>> >> 
>>  
>> I know this syntax doesn’t work in ST3, and I’m guessing it doesn’t in ST4 either. Considering the way parameters and local variables work in many languages, I don’t think allowing this would be unexpected.
>>  
>> Sam
>>  
>> From: Udo Borkowski [mailto:ub at abego-software.de] 
>> Sent: Monday, February 14, 2011 3:21 AM
>> To: Sam Harwell
>> Cc: stringtemplate-interest List
>> Subject: Re: [stringtemplate-interest] [ST4] How to avoid map key iteration?
>>  
>> Hi Sam,
>>  
>> If you write it this way:
>>  ...
>>  <t2(adr=p,line2={<adr.city>, <adr.zip>})>
>>  
>> Good point.
>>  
>> I guess it is just my personal style (and background) that makes me raise the issue. Inside a subtemplate I'd prefer to access the parameters of the subtemplate (the {p1,p2|…}) over the access of something outside of the subtemplate, especially with the dynamic name lookup of ST4 in mind.
>>  
>>  
>> Udo
>>  
> 
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