I've been going through On Lisp by Paul Graham and on page 33 he recommends
against performing "intermediate" bindings. Does this advice hold for Clojure?
Here are a couple examples:
;; Common Lisp (from the book)
(defun bad (x)
(let (y sqr)
(setq y (car x))
(setq sqr (expt y 2))
(list 'a sqr)))
(defun good (x)
(list 'a (expt (car x) 2)))
;; Clojure
(defn bad [x]
(let [y (first x)
sqr (expt y 2)]
(list 'a sqr)))
(defn good [x]
(list 'a (expt (first x) 2)))
Paul Graham explains:
"The final result is shorter than what we began with, and easier to understand.
In the original code, we’re faced with the final expression (list 'a sqr), and
it’s not immediately clear where the value of sqr comes from. Now the source of
the return value is laid out for us like a road map.
The example in this section was a short one, but the technique scales up.
Indeed, it becomes more valuable as it is applied to larger functions."
In clojure you can't do setq of course but I find myself going against this
advice all the time, and I find that it's more important to do so when working
with larger functions. I think introducing names makes code clearer. Here's an
example from my own code:
(defn create-topic
[params]
(let [params (merge params (db/tempids :topic-id :post-id :watch-id))
topic (remove-nils-from-map (c/mapify params mr/topic->txdata))
watch (c/mapify params mr/watch->txdata)
post (c/mapify params mr/post->txdata)]
{:result (db/t [topic post watch])
:tempid (:topic-id params)}))
To my mind, creating bindings for "topic", "watch", and "post" makes the code
easier to understand. When you get to "(db/t [topic post watch])" you don't
have to deal with as much visual noise to understand exactly what's going into
the transaction.
So, is PG's advice any good?
Thanks!
Daniel
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