Aug 18, 2010

A slight modification to Clojure’s comp function gives me more power:

(defn comp+ ([] identity) ([f] f) ([f g] (fn ([] (f (g))) ([x] (f (g x))) ([x y] (f (g x y))) ([x y z] (f (g x y z))) ([x y z & args] (f (apply g x y z args))))) ([f g h] (fn ([] (f (g (h)))) ([x] (f (g (h x)))) ([x y] (f (g (h x y)))) ([x y z] (f (g (h x y z)))) ([x y z & args] (f (g (apply h x y z args)))))) ([f1 f2 f3 & fs] (let [fs (reverse (list* f1 f2 f3 fs))] (fn [& args] (loop [ret (apply (first fs) args) fs (next fs)] (if fs (recur ((first fs) ret) (next fs)) ret)))))) ;; allowing (require ‘clojure.string) (for [f (map #(apply comp+ %) [[keyword name] [] [name clojure.string/upper-case]]) e '[foo bar]] (f e)) ;=> (:foo :bar foo bar "FOO" "BAR")

I added a function body to comp+ handling the case where it’s given no function, returning the identity function. This let’s me use comp+ in more interesting ways without requiring that I handle the case of no arguments explicitly and without exploding when I don’t.

Just one of those little things I guess.

:f