Macro ENSURE

From: Nicolas Neuss (my.name_at_iwr.uni-heidelberg.de)
Date: 07/30/04

Date: 30 Jul 2004 13:51:03 +0200

Hello.

Relatively often I happen to write

(unless x (setf x y))

(setf x (or x y))

and I want to replace this with a macro ENSURE as

(ensure x y)

Since the macro

(defmacro ensure (x y)
`(setf ,x (or ,x ,y)))

has problems with multiple evaluation (e.g. (ensure (aref x (incf i)) 1)),
the best solution should be something like

(define-modify-macro ensure (&rest args) or)

Question 1: Is this allowed by the spec, i.e. is the macro OR allowed to
appear at this place?

Question 2: Is this macro a good idea?

Question 3: Since such a macro might be rather common: is there another
name for it?

Thanks, Nicolas.

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