[stringtemplate-interest] ST map improvement

[Terence Parr]

On Jan 4, 2006, at 6:57 AM, Andrew Goodnough wrote:
> In this case a default of "UNSUPPORTED_OPERATION" is fine but there  
> are other cases where I want the default to just return the key  
> value.  So if it's not in the map, just give me the original value  
> back.  Something like:
>
> opMap ::= [
>  "ADD":"ADD",
>  "CHANGE":"MODIFY",
>  "REMOVE":"DROP",
>  default:key
> ]

Interesting...what if no default meant you get the key?  Actually we  
need this to be consistent with a new syntax for map  
iteration...currently it's a braindead iterate-over-values thing:

<symbols:{s|<s.type> <s.name>}>

what if it's just text to text though?  You really want the keys so  
you can do this with the indirect field accessor:

<aMap:{key|<key> maps to <aMap.(key)>}

Actually, the key is not a "keyword" so no need to make consistent.

> or maybe even better:
>
> opMap ::= [
>  "ADD":"ADD",
>  "CHANGE":"MODIFY",
>  "REMOVE":"DROP",
>  default:<op_key()>  //where op_key() is a defined template
> ]

I like this direction.  Why not map string to arbitrary template  
(string or template name) in general?  Great idea!

> This would make the calling code more readable and concise.   
> Instead of:
>
> <if(it.operation)><opMap.(it.operation)><else><it.operation><endif>
>
> it could be:
>
> <opMap.(it.operation)>

Useful.

> Would this be helpful for anyone else?

An excellent use-case for this option.  What if you want default to  
go to nothing?  I.e., only spit something out if it's in a  
vocabulary?  Do I have a null or something?  Can't remember!

Ter