Hmmm? Maybe (defn if-and [x & tests] (if (every? true? (map #(% x) tests)) x))
for a version that's a function, would short-circuit but for seq chunking, and returns nil or x. Incidentally, I think you can dechunk any seq with (map first (take-while seq (iterate next s))), but haven't tested this. (If s is chunked, it will still be realized in chunks; but if the output is wrapped in (map expensive-fn ...) *that* won't race ahead calling expensive-fn on elements not yet needed by the caller. I think.) On Mon, Jun 10, 2013 at 9:18 PM, Jiaqi Liu <liujiaq...@gmail.com> wrote: > you can just use (every? true? '(arg1 arg2 ....)) or def a simple function > . > i think the Core is powerful enough. > > > 2013/6/11 Cedric Greevey <cgree...@gmail.com> > >> There's also the defmacro route: >> >> (defmacro if-and [test-expr binding & tests] >> `(let [~binding ~test-expr] >> (and ~@(concat tests [binding])))) >> >> Evaluates test-expr, then evaluates to the result of that if the tests >> all pass, and to a falsey value otherwise (in fact, the first falsey value >> returned by any of the tests). If you want only nil or the value, the and >> sexp can be changed to (if (and ~@tests) binding). Short-circuits at the >> first falsey test of course. Might be more convenient (fewer lambdas >> needed) sometimes and more efficient sometimes -- on the other hand, to use >> as a function itself it will need wrapping in a lambda: #(if-and % % >> tests-using-%). >> >> >> >> On Mon, Jun 10, 2013 at 4:31 PM, Ben Wolfson <wolf...@gmail.com> wrote: >> >>> On Mon, Jun 10, 2013 at 1:20 PM, Steven Degutis <sbdegu...@gmail.com>wrote: >>> >>>> Sometimes I've wanted a function that takes a value and a bunch of >>>> tests, and returns it if it passes every test, otherwise nil. >>>> >>>> So I wrote if-and: >>>> >>>> (if-and "foo" >>>> >>>> string? >>>> #(.startsWith % "f") >>>> >>>> >>>> #(.contains % "oo")) >>>> >>>> >>>> ;; => "foo" >>>> >>>> >>>> >>>> (if-and "foo" >>>> string? >>>> #(.startsWith % "f") >>>> >>>> >>>> #(.contains % "NOT IN THE STRING")) >>>> >>>> >>>> ;; => nil >>>> >>>> >>>> Source: >>>> https://github.com/evanescence/if-and/blob/master/src/if_and/core.clj >>>> >>>> Does this seem useful enough to put into core? >>>> >>>> >>> "Takes a value and a bunch of tests, and returns [the value] if it >>> passes every test" implies that (if-and false false?) should return false, >>> but: >>> >>> user> (if-and false false?) >>> nil >>> >>> It's also kind of confusing to me *anyway* that (if-and false false?) >>> would return false and not true (to indicate that the supplied value passed >>> every test). Something like this seems more intuitive to me: >>> >>> user> (defn allpreds [x & ts] (every? #(% x) ts)) >>> #'user/allpreds >>> user> (allpreds false false?) >>> true >>> user> (allpreds nil false?) >>> false >>> >>> With if-and being definable in terms of allpreds: >>> >>> user> (defn if-and* [x & ts] (when (apply allpreds x ts) x)) >>> #'user/if-and* >>> user> (if-and* false false?) >>> false >>> user> (if-and* false nil?) >>> nil >>> >>> -- >>> Ben Wolfson >>> "Human kind has used its intelligence to vary the flavour of drinks, >>> which may be sweet, aromatic, fermented or spirit-based. ... Family and >>> social life also offer numerous other occasions to consume drinks for >>> pleasure." [Larousse, "Drink" entry] >>> >>> -- >>> -- >>> 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 unsubscribe from this group and stop receiving emails from it, send >>> an email to clojure+unsubscr...@googlegroups.com. >>> For more options, visit https://groups.google.com/groups/opt_out. >>> >>> >>> >> >> -- >> -- >> 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 unsubscribe from this group and stop receiving emails from it, send an >> email to clojure+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/groups/opt_out. >> >> >> > > > > -- > > ------------------------------------**** > > 刘家齐 （Jacky Liu） > > ** > > 手机：15201091195 邮箱：liujiaq...@gmail.com > > Skype：jacky_liu_1987 QQ：406229156 > > -- > -- > 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 unsubscribe from this group and stop receiving emails from it, send an > email to clojure+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/groups/opt_out. > > > -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. 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