3 Dec 2009 ingvar   » (Master)

Neat(ish) hack...

Sometimes, I find myself writing anonymous functions, to fill out keyword arguments for functions or adapting the argument order. So, I thought, how hard would it be to write a macro to write the code for me? Turns out, not very complex, at all. The formatting is not QUITE what I started out with, as the Advogato edit box is a bit on the short end, but, hey...

(defmacro _ (form)
 (flet ((is-arg (sym)
	   (and (char= (char (symbol-name sym) 0) #\_)
		 (parse-integer (symbol-name sym)
				:start 1)
   (let ((syms (loop for arg in form
		  for temp = (is-arg arg)
		  if temp collect temp)))
	 ,(mapcar #'cdr (sort syms #'< :key #'car))

With this in hand, you can, for example, easily make an adapter to parse C-style hex constants:

  (_ (parse-integer _1 :radix 16 :start 2))

Not that the lambda-wrapping of this would've been much more complex and I am not entirely sure this wins as far as readability is concerned, but that is as it may be. It's if nothing else a neat macro that would be more than a little tricky to pull off with a less capable macro facility.

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