Hi, Max Mikhanosha suggests a multiple value extension to FINDING... MAXIMIZING &optional INTO: (finding (values x y z) maximizing (complex x y z)) I have good and bad news about that. Bad news first. I plan to reject this patch, based on the following critique of the patch: - Generality: This syntax (VALUES ...) pattern based extension does not cover functions returning multiple values e.g. (finding (floor x y) maximizing (foo x y)) - Arbitrary implementation limit to 9 *result-vars* (MULTIPLE-VALUE-LIMIT is the only one that would make sense, but it's not practical) - A lot more complexity added to the source for just one clause. - Unclear yet whether this syntax extension makes sense for other clauses. - &optional INTO is not integrated. What would it look like? INTO (values a b c) INTO ((values a b c) max) INTO ((a b c) max) - Slight bug: clause as expression must define result and constantly yield either all, or only primary value, e.g. (for (values running-x running-y) = (finding ...)) [if that were the only thing, I'd fix it myself before applying the patch] Now, the good news. Iterate claims to be an extensible iteration facility. Thus I wonder why many contributors in recent years have spent their time understanding and modifying the low-level implementation, instead of using Iterate's documented extension mechanisms? Why not use the following definition? (defmacro-clause (find-values expr maximizing max-expr &optional into vars) "Please don't forget the documentation string here" ;; Not a good design: number of values differs whether or not INTO is used (unless (or vars (eq 'values (if (consp expr) (first expr)))) (error "Expression must start with VALUES: ~S" expr)) (let ((temps (or vars (mapcar #'(lambda (s) (gensym "VALUE")) (rest expr)))) ;;#L(gensym (if (symbolp !1) (symbol-name !1) "VALUE")) (max (gensym "MAX")) (temp (gensym "NEW"))) `(progn (with (,max .,temps)) (let ((,temp ,max-expr)) (when (or (first-time-p) (> ,temp ,max)) (setq ,max ,temp) ;;(multiple-value-setq ,temps ,expr) (dsetq (values .,temps) ,expr))) ,.(if vars () (list `(finally (return (values .,temps))))) ))) This code is much shorter than the proposed patch. If it's not of general usage, it can be embedded in your application code. Your application does not depend on the Iterate maintainers to accept your patch for you to make successful use of Iterate. Doesn't that sound great? Test cases ;(iter(find-values (values x y z) maximizing (complex x y z))) ;(iter(find-values (values x y z) maximizing (complex x y z) into (a b c))) ;(iter (find-values (floor x y) maximizing (rem x y))) ; error ;(iter (find-values (floor x y) maximizing (rem x y) into (q r))) ;(iter (find-values (floor x y) maximizing (rem x y) into ((the integer q) r))) Consider possible extension: destructuring: (dsetq (values a (b . c) d) #) ;(iter(find-values (values x y z) maximizing (complex x y z) into (a (b . c) d))) ; breaks WITH ;(iter(find-values (values x y z) maximizing (complex x y z) into (a (b c) d))) ; breaks WITH What are the drawbacks of this macro w.r.t. a built-in clause? - No type inference (and type-dependent initial values) - No conflict when used together with other default accumulation clauses The first is a general problem of Iterate's API. The second can be remedied as follows, using the technique described in the Iterate manual. With the update below, a conflict of gatherers will result in a "Duplicate variable: RESULT456" error. Not pretty, but better than silence. (defmacro-clause (find-values expr maximizing max-expr &optional into vars) "Please don't forget the documentation string here" ;; Not a good design: number of values differs whether or not INTO is used (unless (or vars (eq 'values (if (consp expr) (first expr)))) (error "Expression must start with VALUES: ~S" expr)) (let ((temps (or vars ;; Bind iterate::*result-var* so Iterate knows it's a gatherer ;; and will signal a conflict with other gathering clauses. (cons iterate::*result-var* (mapcar #'(lambda (s) (gensym "VALUE")) (rest (rest expr)))))) ;;#L(gensym (if (symbolp !1) (symbol-name !1) "VALUE")) (max (gensym "MAX")) (temp (gensym "NEW"))) `(progn (with (,max .,temps)) (let ((,temp ,max-expr)) (when (or (first-time-p) (> ,temp ,max)) (setq ,max ,temp) ;;(multiple-value-setq ,temps ,expr) (dsetq (values .,temps) ,expr))) ,.(unless vars (list `(finally (return-from ,iter::*block-name* (values .,temps)))))))) ;(iter(find-values (values x y z) maximizing (complex x y z))(collect x)) ; error ; I think I'll add that to the testsuite as another example. The latter also shows how to exit from a named loop via iter::*block-name* -- this is not really great, and not documented, but LEAVE does not work inside FINALLY (a bug in the example in the original documentation, recently fixed), because expressions inside finally are not walked (and I don't believe the solution is to walk clauses in FINALLY, as that could lead to infinite loops at run-time with malformed loops). Note another current bug: Cannot have 2 clauses maximizing &optional into maximizing values &optional into at the same time (one exact prefix of another). Who jumps in to fix this? Comments are welcome. - general mechanisms for multiple values? - better API for gatherer into the default value(s) vs. iter::*result-var*? - finally (leave foo) & *block-name* issue? - exact prefix bug caretaker? Regards, Jorg Hohle