Support basic programmatic elements in templates

[xorrkaz]

Requirements

Templates should support conditional expressions and loops/ranges (i.e., iterate over a set of objects). These constructs should be able to operate on variables in addition to YANG data nodes.

Non-Requirements

Andy suggested using XPath for these (e.g., conditionals could be done similarly to "when" clauses). XPath is likely already supported by servers.

That said, XPath notation might not be as easily adopted by users of templates and perhaps consideration could be given to a simpler syntax.

[robertjwills]

This adds a lot of complexity in specification and implementation. It sounds like the suggestion here is that Yang Templates should provide some sort of diluted flavour of XSL, where programmatic concepts such as loops are expressed through a data tree.