I don't know if it will answer your history question, but there was a fairly long discussion about this last year:
https://groups.google.com/forum/?fromgroups=#!searchin/clojure/let-else/clojure/1g5dEvIvGYY/EWjwFGnS-rYJ Cheers, Dave On Fri, Jan 4, 2013 at 7:23 AM, Edward Tsech <edts...@gmail.com> wrote: > Sorry guys, I forget to mention that it should behave like "let" in Clojure > or like "let*" in Scheme. > > I mean e.g.: > (if-let* [x 1 y nil z (inc y)] > (+ x y z) > 0) ; => 0 > ;; (inc y) shouldn't be evaluated here. > > Which means "and" doesn't work there. > In terms of implementation I mean smth like that: > > (defmacro if-let* > ([bindings then] > `(if-let* ~bindings ~then nil)) > ([bindings then else] > (if (seq bindings) > `(if-let [~(first bindings) ~(second bindings)] > (if-let* ~(drop 2 bindings) ~then ~else) > ~else) > then))) > > But anyway I'm more interested in history of that behavior rather than > implementation. > Because for me it seems logical if "let" support more than two forms > "if-let" also could do that. > And I'd like to understand: "Am I wrong or it's just historical reason?" > > Ed > > On Friday, January 4, 2013 1:29:41 PM UTC+6, Andy Fingerhut wrote: >> >> I don't know the history of the answer to "why", except perhaps as hinted >> by Evan's answer, which is that it becomes implicit how to combine the >> results of the multiple values to get the final true/false for the if >> condition. You imply "and", which is a perfectly reasonable choice. >> >> My main reason for responding is to let you know that if you really want >> such behavior, macros let you roll your own without much trouble. >> >> Andy >> >> On Jan 3, 2013, at 10:24 PM, Edward Tsech wrote: >> >> Hey guys, >> >> if-let and when-let macros support only 2 forms in binding vector: >> >> (if-let [x 1 y 2] >> ...) >> java.lang.IllegalArgumentExcepdtion: if-let requires exactly 2 forms in >> binding vector(NO_SOURCE_FILE:1) >> >> Why doesn't "if-let" support any even amount of binding forms as "let" >> does? >> >> e.g. >> (if-let [x 1 y 2 z 3] >> (+ x y z) >> 0) ; => 6 >> >> (if-let [x 1 y nil z 3] >> (+ x y z) >> 0) ; => 0 >> >> Thanks! >> >> > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with your > first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
