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    <p>You can definitely write a macro which uses itself in its own expansion. This makes perfect sense, and it is a natural way to write the COND macro, which has a regular, expanding structure due to the arbitrarily long list of cond pairs, that can be expressed by the usual car/cdr or first/rest recursion.</p> <pre><code>(defmacro new-cond (&amp;rest cond-pairs) (cond ;; you need cond to compile new-cond syntax, LOL! ((null cond-pairs) nil) ((atom cond-pairs) (error "new-cond: bad syntax!")) (t `(if ,(first (first cond-pairs)) (progn ,@(rest (first cond-pairs))) (new-cond ,@(rest cond-pairs)))))) &gt; (macroexpand-1 '(new-cond (1 2) (3 4))) (IF 1 (PROGN 2) (NEW-COND (3 4))) </code></pre> <p>This is very analogous to lazy list processing. <code>macroexpand</code> expands just the outer macro, leaving a "promise" object to continue the expansion. That "promise" object is the macro call <code>(NEW-COND (3 4))</code> at the tail.</p> <p>Of course the real macro expander will walk the whole form and "force" all these promises (unexpanded macro calls) until no more remain.</p> <p>I think there are some advantages to this style, such as easy debugging with <code>macroexpand</code>. You get a small expansion. If its recursive nature is obvious, that's a win. If the macro is such that your brain needs to see the whole thing expanded, it's a loss.</p> <p>Here, I can see that <code>(IF 1 (PROGN 2) (NEW-COND (3 4)))</code> is the correct compile. If 1 is true, evaluate the forms list (2). Otherwise keep going with the other cond pairs. Now we have to verify the one pair case:</p> <pre><code>&gt; (macroexpand-1 '(new-cond (3 4))) (IF 3 (PROGN 4) (NEW-COND)) </code></pre> <p>Excellent, and the no-pair case <code>(NEW-COND)</code>, by obvious inspection, reduces to nil.</p>
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    1. POLisp: can a macro be recursive?
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    1. COYou can lose cond inside new-cond if you use nested if. `(if (null cond-pairs) nil (if (atom cond-pairs) (error "new-cond: bad syntax!") '(if ,(first ...` (before if should be `)
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