In Clojure it is idiomatic to have optional args at the front of the
signature. This makes it easy to define convenient caller APIs, but it
leads to bulky let forms like this one (from clojure.core/defmulti)
(let [docstring (if (string? (first options))
(first options)
nil)
options (if (string? (first options))
(next options)
options)
m (if (map? (first options))
(first options)
{})
options (if (map? (first options))
(next options)
options)
dispatch-fn (first options)
options (next options)
m (assoc m :tag 'clojure.lang.MultiFn)
m (if docstring
(assoc m :doc docstring)
m)
m (if (meta mm-name)
(conj (meta mm-name) m)
m)]
Is it worth capturing this common idiom in a helper function, e.g. pop-
optional-args:
(defn pop-optional-args
[preds args]
(if (seq preds)
(if ((first preds) (first args))
(cons (first args) (pop-optional-args (rest preds) (rest args)))
(cons nil (pop-optional-args (rest preds) args)))
(list args)))
The above let form would then be:
(let [[docstring m dispatch-fn options] (pop-optional-args [string?
map? identity] options)
m (assoc m :tag 'clojure.lang.MultiFn)
m (if docstring
(assoc m :doc docstring)
m)
m (if (meta mm-name)
(conj (meta mm-name) m)
m)]
Worth doing? If so, how could it be better?
Stu
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