Hello Stephen,

the following is a macro defining a function with keyword
arguments. It is called like this:

(defnk foo
   [a b c :x 1 :z 2]
   (println x z))

a, b and c denote positional arguments, 1 and 2 are default
values for x resp. z. This pattern came up several times now,
and there were always some "aha" effects. So it may be a
nice addition to c.c.def.

Here's the macro:
(defmacro defnk
   "Define a function accepting keyword arguments. Symbols up to the  
first
   keyword in the parameter list are taken as positional arguments.  
Then
   an alternating sequence of keywords and defaults values is  
expected. The
   values of the keyword arguments are available in the function body by
   virtue of the symbol corresponding to the keyword (cf. :keys  
destructuring).
   defnk accepts an optional docstring as well as an optional metadata  
map."
   [fn-name & fn-tail]
   (let [[fn-name [args & body]] (name-with-attributes fn-name fn-tail)
         [pos kw-vals]           (split-with symbol? args)
         kw-vals                 (apply hash-map kw-vals)
         de-map                  {:keys (vec (keys kw-vals))
                                  :or   kw-vals}]
     `(defn ~fn-name
        [~@pos & options#]
        (let [~de-map (apply hash-map options#)]
          ~@body))))

The docstring is a bit contorted but I'm too sleepy now,
to get that right...

Sincerely
Meikel

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