Hooke your Clojure functions!
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Robert Hooke

Robert Hooke provides a flexible, composable mechanism by which you can extend behaviour of functions after they've been defined. It's named after Robert Hooke FRS, a founding member of the Royal Society who made many important discoveries in the fields of Gravitation, Microscopy, and Astronomy.

Add this to your project.clj :dependencies list:

[robert/hooke "1.0.2"]

If you would like to make your software extensible using Hooke, all you need to do is provide a convention for namespaces that will get loaded on startup. Then users can place files that call add-hook under a specific namespace prefix (my.program.hooks.*) which they can rely on getting loaded at startup.

Hooke is inspired by Emacs Lisp's defadvice and clojure.test fixtures.


(use 'robert.hooke)

(defn examine [x]
  (println x))

(defn microscope
  "The keen powers of observation enabled by Robert Hooke allow
  for a closer look at any object!"
  [f x]
  (f (.toUpperCase x)))

(defn doubler [f & args]
  (apply f args)
  (apply f args))

(defn telescope [f x]
  (f (apply str (interpose " " x))))

(add-hook #'examine microscope)
(add-hook #'examine doubler)
(add-hook #'examine telescope)

(examine "something")
> S O M E T H I N G
> S O M E T H I N G

Hooks are functions that wrap other functions. They receive the original function and its arguments as their arguments. Hook functions can wrap the target functions in binding, change the argument list, only run the target functions conditionally, or all sorts of other stuff.

Technically the first argument to a hook function is not always the target function; if there is more than one hook then the first hook will receive a function that is a composition of the remaining hooks. But when you're writing hooks, you should act as if it is the target function.


Copyright (C) 2010 Phil Hagelberg and Kevin Downey

Distributed under the Eclipse Public License, the same as Clojure.