`println` always returns `nil`. So it prints "one", returns `nil`, and you try to execute the form:
(nil) => NullPointerException user=> (evens? (println “one”)) one NullPointerException user/eval239 (NO_SOURCE_FILE:74) On Thu, Sep 20, 2018 at 9:06 AM Orestis Markou <ores...@orestis.gr> wrote: > evens? is not a macro, therefore when you do (evens? (println “one”)), the > println will be evaluated first, and its return value, nil, gets passed > into the evens function. > > > 20 Σεπ 2018, 5:44 μμ, ο χρήστης «Stephen Feyrer <stephen.fey...@gmail.com>» > έγραψε: > > Hi, > > I have just been playing around with this idea and I got something. > > user=> (def some-numbers ‘(2 4 6 8)) #This is my value to test later. > #’user/some-numbers > user=> (def evens? (partial (when (apply = (map even? some-numbers))))) > #’user/evens? > user=> (evens? (println “one”)) > one > NullPointerException user/eval239 (NO_SOURCE_FILE:74) > user=> > > What is my mistake? > > Thanks. > > > On 12 December 2017 at 07:52, Stephen Feyrer <stephen.fey...@gmail.com> > wrote: > >> Hi Tim, >> >> Thank you. >> >> >> -- >> Kind regards >> >> Stephen. >> >> On 11 December 2017 at 23:58, Timothy Baldridge <tbaldri...@gmail.com> >> wrote: >> >>> I talked a bit about this in my video on Boolean Blindness: >>> https://www.youtube.com/watch?v=K1LaaJMscCc >>> >>> Might be worth a watch. >>> >>> On Mon, Dec 11, 2017 at 4:56 PM, Stephen Feyrer < >>> stephen.fey...@gmail.com> wrote: >>> >>>> Hi there, >>>> >>>> I have been trying to shake this thought for a while now. Essentially, >>>> my thought was if you can return a function why not decision component of >>>> an IF, WHEN or SOME statement? That would give you a re-usable named >>>> choice. >>>> >>>> Then you could write: >>>> >>>> (celebration: do-something do-something-else) >>>> >>>> >>>> This would be equivalent to writing: >>>> >>>> (def success [apples bananas pears]) >>>> >>>> (defn celebration: [x y] (if (empty? success) x y)) >>>> >>>> (celebration: (do-something do-something-else)) >>>> >>>> >>>> I'm reasonably certain of the foolishness of this thought but >>>> occasionally, I have doubts. >>>> >>>> Maybe I'm barking up the wrong tree or possibly I've seen something >>>> like this before and forgotten about it. Perhaps, this is just taking >>>> things too far... Either way, it's deferring the choice until it's >>>> needed. In the right hands it could make for more readable code. >>>> >>>> For completeness sake, to define the first form above you'd use: >>>> >>>> (defc celebration: (if (empty? success))) >>>> >>>> >>>> A more usable example might look like: >>>> >>>> (def nums [1 2 3 4 5 6 7 8]) >>>> >>>> (defc even-nums: (some (even? nums))) >>>> >>>> I guess this makes the real question, is it a good thing to be able to >>>> defer choice like this? >>>> >>>> >>>> Btw, defc would be like def-choice but other options might be deft - >>>> def-test or defp - def-predicate. >>>> >>>> >>>> -- >>>> Kind regards >>>> >>>> Stephen >>>> >>>> -- >>>> 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/d/optout. >>>> >>> >>> >>> >>> -- >>> “One of the main causes of the fall of the Roman Empire was that–lacking >>> zero–they had no way to indicate successful termination of their C >>> programs.” >>> (Robert Firth) >>> >>> -- >>> 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/d/optout. >>> >> >> > -- > 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/d/optout. > > -- > 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/d/optout. > -- 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/d/optout.
