On Jun 14, 4:40 pm, Alex Osborne <a...@meshy.org> wrote: > Matthew Phillips <mattp...@gmail.com> writes: > > The only way I can think of to write it in Clojure is: > > > (reduce > > (fn [items op] > > (let [items1 (if (:delete op) (drop-index (:delete op) items) > > items)] > > (if (:insert op) (cons (:insert op) items1) items1))) > > items ops) > > > i.e. I'm using a cascade of conditional let's. This isn't _too_ bad in > > this case, but you can image how unreadable this could get. > > To avoid a "cascade of lets" I've occasionally defined a function called > conj-if (or disj-if or assoc-if...). Like so: > > (defn conj-if [coll test x] > (if test (conj coll x) coll)) > > (fn [items op] > (-> (conj-if (foo? op) "one") > (conj-if (bar? op) "two"))) > (conj-if (baz? op) "three"))) >
Yes, I have thought about using -> to chain transformations together, in fact it's a little like what I imagine the ST monad (or is it the State monad?) does by chaining a series of apparent-variable- assignments together. I like this idea, but something about writing "xxx-if" functions doesn't seem right, perhaps due to the number of xxx's there might be. Perhaps I need a "do-if" fn that takes a target, predicate and a transform fn, and applies the transform when pred is true. Will have a think about that. > On the other hand the cascading lets are really not that bad especially > if you pull any complex predicate or value-manipulation logic out into > separate functions: > > (fn [items op] > (let [items (if (foo? op) (assoc items "foo" 1) items) > items (if (bar? op) (dissoc items "bar") items) > items (if (baz? op) (empty items) items)] > items)) Interesting, it hadn't occurred to me that I could just keep shadowing "items" in the same let. Usually I think shadowing is a bad idea, but perhaps it's better than "items1", "items2", etc. Thanks! -- 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
