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Learning Common Lisp (using GNU CLISP 2.43) .. so might be a noob mistake. Example is the 'print prime numbers between x and y' (defun is-prime (n) (if (< n 2) (return-from is-prime NIL)) (do ((i 2 (1+ i))) ((= i n) T) (if (= (mod n i) 0) (return NIL)))) (defun next-prime-after (n) (do ((i (1+ n) (1+ i))) ((is-prime i) i))) (defmacro do-primes-v2 ((var start end) &body body) `(do ((,var (if (is-prime ,start) ,start (next-prime-after ,start)) (next-prime-after ,var))) ((> ,var ,end)) ,@body)) (defmacro do-primes-v3 ((var start end) &body body) (let ((loop-start (gensym)) (loop-end (gensym))) `(do ((,loop-start ,start) (,loop-end ,end) (,var (if (is-prime ,loop-start) ,loop-start (next-prime-after ,loop-start)) (next-prime-after ,var))) ((> ,var ,loop-end)) ,@body ))) do-primes-v2 works perfectly. [13]> (do-primes-v2 (p 10 25) (format t "~d " p)) 11 13 17 19 23 Next I tried using gensym to avoid naming clashes in macro expansion - do-primes-v3. However I'm stuck with a *** - EVAL: variable #:G3498 has no value Tried using macro-expand to see if i could spot the mistake but I can't. [16]> (macroexpand-1 `(do-primes-v3 (p 10 25) (format t "~d " p))) (DO ((#:G3502 10) (#:G3503 25) (P (IF (IS-PRIME #:G3502) #:G3502 (NEXT-PRIME-AFTER #:G3502)) (NEXT-PRIME-AFTER P))) ((> P #:G3503)) (FORMAT T "~d " P)) ;

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