Seems to me that (merge {:attr something} obj) answers the OP's question,
mentions obj only once, and is short and pithy. OTOH it computes the
"something" every time, whether it's needed or not, so in cases where
"something" is expensive to compute (or has side effects that should only
happen if it winds up in the output!) then another method needs to be used.On Sat, May 25, 2013 at 8:08 AM, atkaaz <atk...@gmail.com> wrote: > like: > => (definline pred-transform [obj pred tf] > `(let [o# ~obj] > (if (~pred o#) o# > (~tf o#)))) > #'cgws.notcore/pred-transform > > => (pred-transform (println 1) nil? #(println % ".")) > 1 > nil > => (pred-transform (println 1) #(not (nil? %)) #(println % ".")) > 1 > nil . > nil > > > On Sat, May 25, 2013 at 3:07 PM, atkaaz <atk...@gmail.com> wrote: > >> in which case it does get evaluated twice if form: >> => (pred-transform (println 1) #(not (nil? %)) #(println % ".")) >> 1 >> 1 >> nil . >> nil >> >> => (pred-transform (println 1) nil? #(println % ".")) >> 1 >> 1 >> nil >> >> so maybe a let + gensym would be in order? >> >> >> >> On Sat, May 25, 2013 at 3:04 PM, atkaaz <atk...@gmail.com> wrote: >> >>> Shouldn't it be like: >>> >>> (definline pred-transform [obj pred tf] >>> `(if (~pred ~obj) ~obj >>> (~tf ~obj))) >>> => (pred-transform 1 #(not (nil? %)) println) >>> 1 >>> => (pred-transform 1 nil? println) >>> 1 >>> nil >>> >>> >>> >>> >>> On Sat, May 25, 2013 at 2:55 PM, atkaaz <atk...@gmail.com> wrote: >>> >>>> just wondering if obj is a form does it get evaluated twice? >>>> >>>> >>>> On Sat, May 25, 2013 at 2:51 PM, Jim - FooBar(); <jimpil1...@gmail.com >>>> > wrote: >>>> >>>>> no need for macros... :) >>>>> >>>>> (definline safe-assoc [m k v] >>>>> `(if (contains? ~m ~k) ~m >>>>> (assoc ~m ~k ~v))) >>>>> >>>>> (definline pred-transform [obj pred tf] >>>>> `(if ~(pred obj) ~obj >>>>> ~(tf obj))) >>>>> >>>>> Jim >>>>> >>>>> >>>>> >>>>> On 25/05/13 12:44, atkaaz wrote: >>>>> >>>>> may I see the macro for the latter, if you decide to go that way ? thx >>>>> >>>>> >>>>> On Sat, May 25, 2013 at 2:24 PM, Steven Degutis >>>>> <sbdegu...@gmail.com>wrote: >>>>> >>>>>> There are two patterns I find in my code that I'm still unhappy with >>>>>> but I don't know how to clean up. >>>>>> >>>>>> The first is: (if (:attr obj) obj (assoc obj :attr something)) >>>>>> >>>>>> I'm basically saying, give this hash-map an attribute if it doesn't >>>>>> already have it. And just return the thing with an attribute, regardless >>>>>> if >>>>>> I had to add it or not. >>>>>> >>>>>> This version is ugly because it repeats obj three times. I could >>>>>> write my own macro to de-duplicate it, but I avoid doing that when I can >>>>>> because there's usually a better built-in solution that I just don't know >>>>>> about yet. >>>>>> >>>>>> The second is like it: (if (some-test obj) obj (some-transformation >>>>>> obj)) >>>>>> >>>>>> In this one, I just want to return the object, but maybe transform >>>>>> it first. But the reference to obj happens three times! Still feels like >>>>>> it >>>>>> could be cleaned up. >>>>>> >>>>>> Any thoughts on how to clean these up? >>>>>> -- >>>>>> -- >>>>>> 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. >>>>> >>>>> >>>>> >>>>> >>>>> -- >>>>> -- >>>>> 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. > > > -- -- 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.
