lets vote what to read next joy of clojure 2nd or programming clojure 3rd ed?

Hi all, I am hitting a weird issue with core.spec when trying to add extra assertions to a s/keys spec using s/and. I have been able to make a minimal example of the problem.

(s/def ::bar (s/or :string string?
                   :int int?))
(s/def ::foo (s/and (s/keys :req-un [::bar])
                    (fn [x]
                      (prn x)
                      true)))

(s/explain ::foo {:bar "bar"})
;;=> {:bar [:string "bar"]}
;;=> Success!

(s/explain ::foo {:bar 1})
;;=> {:bar [:int 1]}
;;=> Success!

@sofra That's how s/or works.

It conforms the value into a data structure that shows how it matched the spec.

thanks @seancorfield I sort of understood that, I didn’t realise it got conformed and passed the conformed value through each predicate in the s/and.

user=> (require '[clojure.spec.alpha :as s])
nil
user=> (s/def ::bar (s/or :string string? :int int?))
:user/bar
user=> (s/conform ::bar 42)
[:int 42]
user=> (s/conform ::bar "42")
[:string "42"]
user=>                  

Yes, s/and flows values through so if something conforms a value, that is what's passed on to the next predicate.

ahhh, ok thanks I didn’t understand that part. Thanks!

hi, i can't see how read-string can possibly execute code without using the eval. (read-string "(+ 1 1)") evals to a list (+ 1 1). "(+ 1 1)" is the user input.

(read-string "#=(+ 2 3)") => 5

could someone explain how this gets evaluated?

@tomaas I’m not sure I fully understand the question, but “#=” is the read-eval literal and calls eval here: https://github.com/clojure/tools.reader/blob/master/src/main/clojure/clojure/tools/reader.clj#L588 more notes, https://github.com/clojure/tools.reader/blob/master/src/main/clojure/clojure/tools/reader.clj#L866

@mhuebert thanks. read-string is called at runtime parse the this string and return a reader macro expresion. But arent macros expanded at compile time? I dont get how that parsed expression gets run

@tomaas reader macros aren’t the same as macros, they are handled at read-time

how many phases does the 'runtime' compile executable have then? read-time + eval-time?

well, if you have eval then you have all the phases, no?

maybe some of the info on this page will help https://stackoverflow.com/questions/5669933/is-clojure-compiled-or-interpreted#5670203

> the dynamic and interactive nature of Clojure that means you can invoke the compiler at run-time if you want to. This is all part of the Lisp “code is data” tradition.

ls

is there a way to use a leiningen profile in a macro?

is there some doall + map macro? Similar to run!, but the return the collection?

What are you trying to do?

(doall (map #(..) col))

if i didn't need the result, i could do (run! #(...) col)) which is nicer

im looking if there is something similar

One way is to use mapv instead of map. It’s eager. Another is to use transducer version (into [] (map #(...)) coll)

Third would be to use reduce instead of map.

last time someone asked a similar question, I think the most Clojure-y answer was to use a transducer

Heh, tried this out of curiosity and it works. You can use normal function composition.

user> (def doall-map (comp doall map))
#'user/doall-map
user> (doall-map #(or (println %) %) [1 2 3])
1
2
3
(1 2 3)

This might have some serious caveats though, I’m not sure. Personally I like the transducer version most.

Depending on the situation of course.

cool

🙂

Hello, I’m used to the cond from Scheme, does the cond in Clojure support the => syntax?

@duncanmak I'm not familiar enough with Scheme to know what that syntax means -- could you explain?

like, in Scheme: (cond ((re-match ...) => (lambda (match) ...))) if-let feels a bit like it, but it only allow one test

Ah, take a look at condp and see if that's closer to what you're looking for...

I found https://github.com/Engelberg/better-cond, but I don’t wanna take on a library

yeah, i was looking at condp, but it doesn’t seem to capture the result from the test

are you sure? its result-fn, which must be a unary function, is called with the result of the predicate as its argument

oh hmm

let me try

i want to access the result in the consequent part

(condp = 4
  2 :>> #(println '2 %)
  4 :>> #(println '4 %))

oh oh

BTW, it's better not to post the same question in multiple channels -- so folks in one channel don't have to spend time answering something that was already answered elsewhere.

@duncanmak Did condp solve your needs?

i’m gonna give it a try, thanks!