Println returns nil

Vargs are a seq not a list, technically

And while there is such thing as an empty seq now in clojure, it wasn't always the case, there was only nil

And in many cases and places things still operate like that is the case, and it is mostly fine

@UK0810AQ2 it prints 2 nils, first nil being the c and the second being the return value of println

@U03N4NQ0PCH aye, my bad, misread the question, sorry

%& is a seq of the rest of the arguments

And + operates on numbers, not seqs of numbers

ohhh, ok thanks

So apply is what you want.

(def sum2 #(apply + %&))

i see, thank you

Btw, I never noticed it before, but (apply + nil) as well as (apply + '()) and (+) return 0, so nil behaves like an empty sequence here (which would be consistent to the behaviour of the empty vararg in your previous question). But (+ nil) returns nil.

(apply + nil) should be (apply + '(nil)) to be the equivalent to (+ nil). And its returns nil.

Yeah it does make sense. I just find it a bit weird that nil and '() work the same way in args given that in Clojure they are not equal like in some other Lisps.

OK I see, interesting catch indeed.

I think your question is a bit opaque. Clojure maps values are not realized until accessed. So your map, until you call something like ((get-in (get-user-details 123) [:result :details])) will never have actually called the database. its at that point you would call the execute command. If you want to force the queries to run when you call the function, you can wrap your functions with doall and that will force them to execute. The parallel part however is not handled here. You could use pmap to iterate over the functions you want to call then it would be paralleled. However, I think parallelizing query calls like this might be a bit of a code smell. At least to me, it seems like something would be off if doing this.

I may have been mistaken, one second while I look into this again

Right so, maps are eager but map is not which is where I got confused. Parallelizing the executions is something you could do in some form with https://clojuredocs.org/clojure.core/pmap

what do you want to sort? the result of group-by or values of the result?

basically if the map is as below , i would like to do a group-by first and then apply sort for uri which is of type string

(def a [{:user-id 1 :uri "/zinc"}
        {:user-id 2 :uri "/account"}
        {:user-id 1 :uri "/foo"}])

(group-by :uri a) will give you a map of uri to the list of maps. How do you expect it to be sorted?

i was looking into the article https://stackoverflow.com/questions/47847937/cleaner-way-to-sort-and-order-a-vector-of-maps-in-clojure

(def my-maps
    [{:name "jess", :age 32} 
     {:name "ruxpin", :age 4} 
     {:name "jess", :age 35} 
     {:name "aero", :age 33} 
     {:name "banner", :age 4}])

(update-vals (group-by :name (sort-by :age my-maps)) last)

Thanks @U04V4KLKC, What information you need ?

> (group-by :uri a) will give you a map of uri to the list of maps. How do you expect it to be sorted?

hmmmmm, how that is being sorted in stackoverflow? i am writing the code referring stack flow post,

This is going to be the result of your group-by with uri 👇

{"/zinc" [{:user-id 1, :uri "/zinc"}], 
 "/account" [{:user-id 2, :uri "/account"}], 
 "/foo" [{:user-id 1, :uri "/foo"}]}

👍