Andrew Dunstan <and...@dunslane.net> writes:
> Looks good. Perhaps the comments above the UNBOUNDED precedence setting
> (esp. the first paragraph) need strengthening, with a stern injunction
> to avoid different precedence for non-reserved keywords if at all possible.
OK. How about rewriting that first para like this?
* Sometimes it is necessary to assign precedence to keywords that are not
* really part of the operator hierarchy, in order to resolve grammar
* ambiguities. It's best to avoid doing so whenever possible, because such
* assignments have global effect and may hide ambiguities besides the one
* you intended to solve. (Attaching a precedence to a single rule with
* %prec is far safer and should be preferred.) If you must give precedence
* to a new keyword, try very hard to give it the same precedence as IDENT.
* If the keyword has IDENT's precedence then it clearly acts the same as
* non-keywords and other similar keywords, thus reducing the risk of
* unexpected precedence effects.
*
* We used to need to assign IDENT an explicit precedence just less than Op,
* to support target_el without AS. While that's not really necessary since
* we removed postfix operators, we continue to do so because it provides a
* reference point for a precedence level that we can assign to other
* keywords that lack a natural precedence level.
regards, tom lane
