Useful has functions that do this and more: fix or to-fix, according to taste. Your iffn is just the three-argument case of to-fix: (def magnify (to-fix pos? inc dec)). But fix and to-fix accept more or fewer arguments as well, so that (fix x pos? inc) is like (if (pos? x) (inc x) x), and (to-fix tall? shorten thin? fatten) is (fn [x] (cond (tall? x) (shorten x) (thin? x) (fatten x) :else x)).
Basically both of these functions look through their clause pairs and apply the first transform whose test matches. fix takes its "focus" argument immediately, while to-fix returns a lambda that performs the requested operation. On Tuesday, February 19, 2013 9:53:57 PM UTC-8, James MacAulay wrote: > > Sometimes I find myself writing code like this: > > (defn magnify [n] (if (pos? n) (inc n) (dec n))) > > ...and I want to get rid of all those "n"s. I've looked for a macro like > this, but couldn't find it, so I wrote it: > > https://gist.github.com/jamesmacaulay/4993062 > > Using that, I could re-write the above like this: > > (def magnify (iffn pos? inc dec)) > > I can imagine a condfn macro, too: > > (def magnify2 (condfn pos? inc > neg? dec > :else identity) > > Has this kind of conditional function composition been explored much? I > couldn't find anything like it in the standard library, but maybe I wasn't > looking hard enough. > > Cheers, > James > -- -- 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 --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
