Hi, Thanks for many examples!
At Thu, 17 Nov 2005 17:31:06 -0000, Thomas Chust wrote: > For example > (lazy-let ((a (get-a))) > (let ((a (get-something-else))) > (if (condition) a #f))) > always evaluates (get-a) even though it is never needed, because it > macroexpands into > (begin > (let ((a (get-a))) > (let ((a (get-something-else))) > (if (condition) a #f)))) This one is OK for me, it just did nothing. > A more academic example can also generate invalid code: > (lazy-let ((a (get-a))) > (let ((a (get-something-else))) > (do-something-unrelated))) > transforms into > (begin > (let (((get-a) (get-something-else))) > (do-something-unrelated))) Oh, this is a big problem. I didn't know that. I have expected such a limitation. > The same type of problem also occurs with this kind of expression: > (lazy-let ((a (get-a))) > (if (condition) a 'a)) > transforming into > (begin > (let ((a (get-a))) > (if (condition) a 'a))) Yes, you are right. It also occurs with "a". > where we have evaluation in unnecessary cases again. Or even worse > with another academic example: > (lazy-let ((a (get-a))) > 'a) > transforming into > (begin > '(get-a)) Ah, how bad. Another counter example could be made by combining with other macros that do some dynamic code creation. > I cannot think of an easy way to fix this without having to make the > macro quite syntax-aware, though. Therefore I would rather suggest to > implement the whole thing for regular let forms in one of the compiler's > optimization passes ;) I first thought this was an optimization issue in the complier, but it might be not, because in some case there is a side effect, while assigning let variables. If it is possible for the compiler to optimize with the normal let, I would prefer it. Would it be worth improving the lazy-let macro so that it understands at least let and quote forms? Daishi _______________________________________________ Chicken-users mailing list [email protected] http://lists.nongnu.org/mailman/listinfo/chicken-users
