On Mon, Oct 10, 2011 at 2:43 PM, Steve Miner <stevemi...@gmail.com> wrote:
> I've just been playing around a bit with match so please forgive me if I've > missed some prior discussions regarding issues that are considered settled. > > One of my first attempts was to match a vector of two of the same thing > using a pattern like [a a]. I naively thought that would imply an equality > constraint between the two items, but in fact each variable matched anything > independently. I now understand that the pattern variables are considered in > different scopes, but I think it's confusing. It's reasonable that you want > something faster than unification for simple literal patterns, but this to > my mind is a special case that's likely to trip people up. > I would accept a patch that would make equality constraints work. We would have to track "named wildcards" and if they are reused, impose the constraint. > In any case, if using multiple pattern variables of the same name does not > imply an equality constraint, I suggest that it be considered an error to > reuse a pattern variable. It's better to throw than to yield an unexpected > match. > In the meantime throwing an error if names are reused in a pattern row is a good idea. http://dev.clojure.org/jira/browse/MATCH-30 > Regarding OR patterns, I didn't really like the infix notation, (1 | 2). > As a lisper, I'd prefer to use something like (or 1 2), or maybe even a > Clojure set notation: #{1 2}. I'm guessing you already thought about this > and made your decision on syntax, but I thought I'd throw it out there. > Set notation doesn't communicate that order is important. (or 1 2) overloads the meaning of the or construct. I'm not sold on the infix notation either. Looking for more feedback / ideas on this. > 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. > It would be nice to lose the extra parens - patch welcome :) > As others have suggested, I agree that returning nil when nothing matches > makes sense. That was my original expectation. > > It was common when testing to wrap a let around the match so I made a > little macro to save a few characters. Free for anyone who wants it. :-) > > (defmacro match-let [bindings & body] > (let [bindvars# (take-nth 2 bindings)] > `(let ~bindings > (match [~@bindvars#] > ~@body)))) > > > Steve Miner > stevemi...@gmail.com match-let looks good. I see that you are Clojure contributor - I'm more than happy to include this. Steve, this is great feedback - much appreciated. David -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
