Matthew Phillips <[email protected]> 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")))
That could be generalized, but I've so far never gotten into a situation
where I've felt the need to.
(defn call-if [x test f & [args]] ; needs a better name
(if test (apply f x args) x))
(fn [items op]
(-> (call-if (foo? op) assoc "foo" 1)
(call-if (bar? op) dissoc "bar")
(call-if (baz? op) empty)))
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))
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