Hmmm... if we take a look at the first arglist...
[name doc-string? attr-map? [params*] body]
Each of this expects a different type of object right?
name - clojure.lang.Symbol
doc-string? - java.lang.String
attr-map? clojure.lang.IPeristentMap
params* - IPeristentVector
body - IPerisistentSeq
What if we used c.c.seq-utils/group-by with class? This would create
hash map with the appropriate values options in it. From there it's a
simple matter of processing a map. I think that the aritiy overloaded
version of defn is easy enough to detect to. Would that do the trick?
Sean
On Dec 29, 1:15 pm, Rich Hickey <richhic...@gmail.com> wrote:
> On Sat, Dec 19, 2009 at 3:58 PM, Stuart Halloway
>
>
>
>
>
> <stuart.hallo...@gmail.com> wrote:
> > 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?
>
> It's tough to guess as to the general applicability of this. One thing
> for sure, it's not really about args, more like a 'take-' or 'split-'
> variant. Finding a good name might point the way towards a general
> utility.
>
> Rich
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