[stringtemplate-interest] [attr:tpl];separator

[Terence Parr]

Added bug reports:

http://www.antlr.org:8888/browse/ST-41

and

http://www.antlr.org:8888/browse/ST-42

IF is defined to return a blank string, though we could make an  
exception inside [...] perhaps.

Ter

On Aug 1, 2008, at 2:07 AM, Roman Odaisky wrote:

> On Friday, 01.08.2008 01:35:58 Terence Parr wrote:
>> On Jul 31, 2008, at 2:08 PM, Roman Odaisky wrote:
>>> Greetings,
>>>
>>> Having gotten StringTemplate to work with Django, I wanted to make a
>>> list of
>>> certain data.
>>>
>>> If I write something like
>>>
>>> $[obj.color, obj.size, obj.volume]; separator=" | "$
>>>
>>> I get
>>>
>>> Yellow | Large | 42
>>>
>>> as intended. But then I wanted to modify the presentation of one of
>>> the
>>> attributes, namely, to append the unit to the number. I tried using
>>> obj.volume:{$it$ m³} and that didn’t work, neither did anything  
>>> else I
>>> attempted.
>>
>> ST might not allow arbitrary expressions within the list constructor
>> [...], although that doesn't sound like something I would miss. Did
>> you try obj.volume:{x | $x$ units} ?
>
> The template $[a:{$it$}]$ throws antlr.RecognitionException, which  
> then
> happens to be obscured by this:
>
> File "/usr/lib/python2.5/site-packages/stringtemplate3/language/ 
> ActionParser.py",
> line 887, in list_
>    self.reportError(ex)
>
> File "/usr/lib/python2.5/site-packages/stringtemplate3/language/ 
> ActionParser.py",
> line 75, in reportError
>    if group == stringtemplate3.StringTemplate.defaultGroup:
> AttributeError: type object 'StringTemplate' has no attribute  
> 'defaultGroup'
>
> (a bug?). $[a:{x|$x$}]$ doesn’t work as well.
>
>>> What is the right way to include the result of template application
>>> to a list?
>>>
>>> Or, say, I want to achieve the same thing this template does:
>>>
>>> A=$a$, B=$b$, C=$c$, D=$d$
>>>
>>> except if any of a, b, c or d attributes are null, their entries
>>> must not be
>>> shown, like this:
>>>
>>> A=1, B=2, D=4
>>
>> You'd have to put $if(a)$A=$a$$endif$ and so on.
>
> Do I understand correctly that $if(an_undefined_attribute)$  
> something $endif$
> is either “something”, or an empty string, but never a null value?  
> And if ST
> encounters such a value in a list, it doesn’t omit it?
>
>>> Is there a way to construct a list from constant strings in the
>>> template? If
>>> there were such a list, I would have written
>>>
>>> $["A", "B", "C", "D"],[a, b, c, d]:{ k, v | $k$=$v$}; separator=",  
>>> "$
>>>
>>> Indeed I’ve just checked after having written this, and this exact
>>> notation
>>> worked, much to my surprise as it doesn’t seem to be documented
>>> anywhere.
>>> Though it doesn’t solve the problem completely: if an attribute from
>>> the
>>> second list is null, the corresponding item from the first one isn’t
>>> removed.
>>
>> Right.  ST assumes that the parallel lists have the same size.
>>
>> You could make or pass in a map that mapped iteration to units:
>>
>> units ::= [
>> 	"1" : "A",
>> 	"2" : "B"
>> 	...
>> ]
>>
>> and then do units.(i) inside an iteration where i is an implicitly
>> maintained loop iteration variable. Naturally, the solution is icky.
>>
>> Try:
>>
>> $["A", "B", "C", "D"],[a, b, c, d]:{ k, v | $if(v)$$k$=$v$$endif$};
>> separator=", "$
>
>>>> st = StringTemplate('$["A", "B", "C", "D"],[a, b, c, d]:{ k, v |
> $if(v)$$k$=$v$$endif$}; separator=", "$')
>>>> st['a'] = 'aa'
>>>> st['b'] = 'bb'
>>>> st['d'] = 'dd'
>>>> print unicode(st)
> A=aa, B=bb, C=dd,
>
> My suggestion would be to make sure lists allow calling templates  
> like this:
>
> $[a, b:someTemplate(), c]$
> or even
> $[a, [b1, b2]:someTemplate(), c]$
>
> And if b were missing (if it would fail the $if(b)$ test), then the  
> template
> wouldn’t be applied to it at all, and the list would contain one  
> less item.
> (Those who need it to be applied even if the attribute is empty,  
> will simply
> use $[a, {$b$}, c]$.) Is it feasible?
>
> I’m currently developing a Web site and I have to display some text  
> in a line
> with separators between groups. But I guess such a feature as I  
> suggested
> above would be useful elsewhere. For example, in generating Python  
> code with
> named arguments:
>
> call ::= "some_function(<[a:{aa=<a>}, b:{bb=<b>}, c:{cc=<c>}, d: 
> {dd=<d>}];
> separator= ", ">)"
>
> call(a=1, b=2, d=4) <! some_function(aa=1, bb=2, dd=4) !>
>
> -- 
> WBR
> Roman.
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