http://dev.clojure.org/jira This file is an XML representation of an issue en-us 4.4 649 25-07-2011 http://dev.clojure.org/jira/browse/MATCH-32 core.match <p>On the Clojure mailing list I wrote:</p> <p>For guards, I wonder if the extra parens are really necessary. Couldn't the :when bind tightly to the previous pattern variable? Like Clojure FOR comprehensions. I think it would be easier to read that way. Same comment applies to :as. To cover the rare case of matching a literal :when or :as, you could quote it or use it as the first item in an OR pattern.</p> <p>On Oct 10, 2011, at 3:11 PM, David Nolen wrote:</p> <p>It would be nice to lose the extra parens - patch welcome <img class="emoticon" src="http://dev.clojure.org/jira/images/icons/emoticons/smile.gif" height="20" width="20" align="absmiddle" alt="" border="0"/></p> MATCH-32

Allow flattened pattern syntax at top-level to avoid nesting :when and :as

Enhancement Minor Resolved Completed Unassigned Steve Miner Wed, 12 Oct 2011 10:28:44 -0500 Fri, 21 Oct 2011 18:53:52 -0500 Fri, 21 Oct 2011 18:53:51 -0500 0 1 <p>I attached a patch that groups the :when and :as terms appropriately given a "flattened" syntax. That is, <span class="error">&#91;a :when even?&#93;</span> becomes <span class="error">&#91;(a :when even?)&#93;</span> before being processed as usual. I only applied it to the top-level of the pattern row because I was concerned about recursive performance and things can get pretty complicated so maybe the magic isn't worth it.</p> <p>Only :when and :as at the top level get any special treatment. No mangling for :seq or ::vector, etc. No mangling of nested patterns.</p> <p>I also added a couple of tests for my changes.</p> <p>I wrote an improved patch that should handle nested patterns as well. Still only groups :when and :as, not :seq since that seems sort of special.</p> <p>Better to use seq? instead of list?</p> <p>At first glance this looks pretty neat! Will try to take a deeper look today. Thanks!</p> <p>One issue I have with this syntax enhancement - how does one match :when or :as as literals?</p> <p>The patch tries to group the :when or :as if that makes sense. If it doesn't make sense <span class="error">&#91;:when true nil&#93;</span>, it leaves it alone so that would match the literal. In the rare case where it would be ambiguous, you would have to use a single OR pattern to get a literal match, such as <span class="error">&#91;a (:when |) false&#93;</span>. I put something like that in one of my new tests.</p> <p>By the way, it might be nice to allow a single element list to match that single pattern. That is, treat <span class="error">&#91;(p)&#93;</span> the same as <span class="error">&#91;p&#93;</span>. Right now, it's considered an error. It would also simply my patch, where I had to introduce interpose1 (as a variant of interpose) to handle an edge case with the OR pattern.</p> <p>I'm not a fan of (:when |). I'd prefer it if the patch included support for always matching literal keywords that are written as ':foo.</p> <p>Revised patch to support ':when (and quoted keywords in general) to match the literal keyword. Updated against HEAD.</p> <p>Fixed, <a href="https://github.com/clojure/core.match/commit/d69abfaf68a86d5b9d73070e666720770779118f">https://github.com/clojure/core.match/commit/d69abfaf68a86d5b9d73070e666720770779118f</a></p> Approval Ok Global Rank Patch Accepted