What are first class functions in clojure?

values which implement clojure.lang.IFn?

more generally, the idea that you can think of functions as values at all, which is a hallmark of “functional” languages

e.g. (let [double (fn [x] (* x 2))] (prn double) (double 4))

is both treating double as a value (because I can call prn on it) and a function (because I can call it on 4)

@suryapjr for example, in java the method foo when you call Bar.foo() is not first class - you can't do anything with .foo itself, you can't pass it to another method or store it for later

(there are reified reflective objects that "represent" a method but that's a whole other thing and not what people are typically using)

a clojure function is an object, so you can pass it as an argument, store it, return it, etc. etc. etc.

Any tips on exposing your Clojure code to be run from a python program? 🙂

@greg316 thanks !

@noisesmith thanks !

My clojure project structure : /name/src/core.clj

How do i run core.clj via clojure REPL

not leiningen , only clojure REPL?

@suryapjr inside the running repl you can run (load-file "/home/src/core.clj")

if you need to require other files you'll also need to set the proper classpath on jvm startup

@noisesmith cool..how do i run the main function

once you have loaded the file into the repl you can run it by the full namespaced name - or if you don't have an ns form in the file, just run it directly because it was defined in your current ns

I have defined ns

I want to run it from the REPL

OK - so call it by the full name, if it's called main and is in foo.bar ns, call (foo.bar/main)

CompilerException java.lang.RuntimeException: No such var: name/main, compiling:(NO_SOURCE_PATH:5:1)

My core.clj:

(ns name)

(defn -main []
(println "Whats your name ?")
(def name read-line)
(str "Hi " "" name) ) 

then call (name/-main)

it's not called main, it's called -main

Beautiful thank you !

And if i want distribute this for others to use ..i need to package it into a jar ?

yeah, jars are the normal way. But for others to use it, be sure you don't have a single segment namespace - make sure it has a meaningful ns with more than one part

and also put it in a path that is relative to the ns

lein uberjar

yes, that's the easy way to make a jar, but so far pooboy was explicit about how to do things without lein

Ah. Didn’t read far enough up the thread.

Right @noisesmith

can i do it without lein?

pooboy yeah - using the jar command line program - you can find out how to use that via google or the manual page, I have only used it minimally myself

also most pople use their jars via maven, which gets more complicated and you start to see why people use leiningen

Cool

maven requires certain conventions be followed, specific documents and formats and folders in the jar etc.

Thank you ! You guys have been very helpful

it's refreshing to answer "how to do this with the simplest tools" rather than "what's the easy way" once in a while, heh

May I ask why you are avoiding lein?

Heheh

And in the below code .. My core.clj:

(ns name)

(defn -main []
(println "Whats your name ?")
(def name read-line)
(str "Hi " "" name) ) 

When i run it .. i get .. user=> (name/-main) Whats your name ? "Hi clojure.core$read_line@19321e2" user=> ( def x read-line) #'user/x user=> x #object[clojure.core$read_line 0x19321e2 "clojure.core$read_line@19321e2"]

Why is the prompt not stopping for my input ?

because read-line is a function, and functions are values

to call functions, you need parens

also, as an aside, def creates globals, it's OK for simple learning examples but breaks easily in real code - for local values there's let

@suryapjr to be clear read-line is just a function (it has a weird name with a @ and number in it), (read-line) actually calls the function

Ohh..cool @noisesmith

I am about to go take a bus home, I'm sure other people can help

Sure thing !

(ns name)

(defn -main []
(println "Whats your name")
(def name (read-line))
(str "Hi " "" name)



)

user=> (name/-main) Whats your name ? "Hi clojure.core$read_line@19321e2"

Why is the read-line function not getting called ?

@suryapjr That code works for me. Recommend using let instead of def inside the fn.

Let me try

Still getting :

Whats your name ?
"Hi clojure.core$read_line@19321e2"

Hmm. That looks like it is running your older -main from above.

Does it block and read a line of input?

No its not waiting for input

Let me reload the REPL

@suryapjr If you revise your code to use let instead of def it would look like this

(defn -main []
  (println "Whats your name ?")
  (let [name (read-line)]
    (str "Hi " "" name)))

I implemented A* algorithm to solve the n-puzzle problem. It works for 3x3 puzzles fine. However, when I try to solve a shuffled 4x4 puzzle, the browser runs out of memory. Here’s the core A* functions:

(defn- make-mm [vals]
  (into (sorted-map)
        (into []
              (map #(vec [(first %) (set (rest %))]) vals))))

(defn- A* [open closed dim]
  (when (not (empty? open))
    (let [[key node] (first-multi open)
          puzzle (first node)]
      [key node]
      (if (solved? (first node))
        (reverse (create-path node []))
        (let [open (dissoc-multi open (nth node 3) node)
              closed (conj closed puzzle)
              neighbors (get-neighbors puzzle dim)]
          (recur
            (reduce
              (fn [coll neighbor]
                (let [g (+ 1 (nth node 2))
                      f (+ g (heuristic neighbor dim))]
                   (assoc-multi coll f [neighbor node g f])))
              open
              (map #(when (nil? (get closed %)) %)
                neighbors))
            closed
            dim))))))

(defn solve [start dim]
  (let [closed #{}
        f-start (heuristic start dim)
        open (make-mm [[f-start [start nil 0 f-start]]])]
    (if-let [path (A* open closed dim)]
      (let [p1 (vec path)
            p2 (into [(first p1)] (pop p1))]
        (rest (map #(get %2 (.indexOf %1 0)) p2 p1))))))

The app is here: https://n-block-puzzle.herokuapp.com/

@mfikes it worked with let !! Thanks !

Cool!

It should also work with def

A consequence, though, is that each time you run the function, if you are using def it redefines a name var:

name=> (-main)
Whats your name
Mike
"Hi Mike"
name=> name
"Mike"
name=> (-main)
Whats your name
Surya
"Hi Surya"
name=> name
"Surya"

hey all, I'm having trouble using a nodejs library in a clojurescript project using leiningen

but I get this error:

Caused by: clojure.lang.ExceptionInfo: No such namespace: twit, could not locate twit.cljs, twit.cljc, or Closure namespace "twit" in file src/twitter_unfollower/core.cljs {:tag :cljs/analysis-error}

I've tried adding it to my project.clj

(defproject twitter-unfollower "0.1.0-SNAPSHOT"
  :description "Jim's bot"
  :url ""
  :dependencies [[org.clojure/clojure       "1.8.0"]
                 [org.clojure/clojurescript "1.8.51"]
                 [org.clojure/core.async    "0.2.395"]
                 [io.nervous/cljs-lambda    "0.3.5"]
                 [cljs-http "0.1.44"]]
  :plugins [[lein-cljsbuild "1.1.4"]
            [lein-npm       "0.6.0"]
            [lein-doo       "0.1.7"]
            [io.nervous/lein-cljs-lambda "0.6.6"]]
  :npm {:dependencies [[source-map-support "0.4.0"]
                       [xhr2 "0.1.4"]
                       [twit "2.2.9"]


                       ]}

  :source-paths ["src"]
  :cljs-lambda
  {:defaults      {:role "arn:aws:iam::954459734159:role/cljs-lambda-default"}
   :resource-dirs ["static"]
   :functions
   [{:name   "cljs-twitter-unfollower"
     :invoke twitter-unfollower.core/run-lambda}]}
  :cljsbuild
  {:builds [{:id "twitter-unfollower"
             :source-paths ["src"]
             :compiler {:output-to     "target/twitter-unfollower/twitter_unfollower.js"
                        :output-dir    "target/twitter-unfollower"
                        :source-map    true
                        :target        :nodejs
                        :language-in   :ecmascript5
                        :optimizations :none}}
            {:id "twitter-unfollower-test"
             :source-paths ["src" "test"]
             :compiler {:output-to     "target/twitter-unfollower-test/twitter_unfollower.js"
                        :output-dir    "target/twitter-unfollower-test"
                        :target        :nodejs
                        :language-in   :ecmascript5
                        :optimizations :none
                        :main          twitter-unfollower.test-runner
                        :npm-deps { :twit "2.2.9" }
                        :install-deps true}}]})

is there something else I'm missing?

I try to require it like a normal namespace

(ns twitter-unfollower.core
  (:require [cljs-lambda.util :as lambda]
            [cljs-lambda.context :as ctx]
            [cljs-lambda.macros :refer-macros [deflambda]]
            [cljs-http.client :as http]
            [cljs.nodejs :as nodejs]
            [cljs.core.async :as async :refer [<!]]
            [twit :as twit])
  (:require-macros [cljs.core.async.macros :refer [go]]))

@derpocious My only comment is that many developers are transitioning to using the new NPM dependencies capability built directly into ClojureScript 1.9.946

thanks 🙂

I would really like to be able to use it in this 1.8 project though

out of curiosity, are there any good articles on the new way?

@derpocious https://clojurescript.org/news/2017-07-12-clojurescript-is-not-an-island-integrating-node-modules

thanks, I've read that article and added the :npm-deps, but I'm getting the same error 😕

I also found this nice clojure twitter api https://github.com/adamwynne/twitter-api, but it is not cljs so I don't think I can use it 😕

Very strange. I just tried adding another node library with [node-twitter "0.5.3"]

https://www.npmjs.com/package/node-twitter

When I add that only to the project.clj :npm { :dependecies it does compile fine, and I even see the node package being downloaded in the console

but then when I try to require the namespace in my code it says it can't find the namespace 'node-twitter'

Is there a shorter or a more elegant way to do this?

(reduce #(if (even? %2) (assoc %1 %2 (+ %2 50)) %1) {} [1 2 3 4 5])
--> {2 52, 4 54}

Basically, I’m interested in the form:

(reduce #(if <condition> (assoc %1 %2 <calculation> %1) {} <collection>)

@duminda Shortest is probably #(conj %1 (when (even? %2) {%2 (+ %2 50)}))

Elegant is: #(cond-> %1 (even? %2) (assoc %2 (+ %2 50)))

How to use clojure for scripting?

clojure itself isn't that great for it due to it's long startup time. It can be used though, just build an uberjar and then execute it. However, you can use ClojureScript for this via lumo https://github.com/anmonteiro/lumo

Cool. Thanks !

And.. What is arity overloading

; this
(defn foo
  ([x] (println x))
  ([x y] (println x y)))

now you can call foo with one or two arguments but no more

both calls end up into different function body where you can do different things if you so choose

I think the most common use case for it is something like this:

(defn hello
  ([] (hello "World"))
  ([n] (println "Hello," n)))

which will print "Hello, World" when called without arguments (hello) but you can call it also with an argument like (hello "Slack") which would print "Hello, Slack"

Very clear thanks !

np

It's amazing how clojure is making a lot of sense to me now ...

Earlier I was petrified of looking at its parentheses

first you learn to not see the parenthesis, then you learn to love them and after that no other syntax makes any sense anymore

Lol...i would love to be in that mode !

And when people say the clojure being lisp is extensible,what do they mean?

well, for example defn in clojure is just a macro

Clojure has I think only 13 language reserved words or characters

rest of the language is built with macros

and functions

gtg bbl

Sure !

how do you debug problems with clojure-compiler concerning externs?

ns fun)

(defn -main []
(println "Hello")
(println "What do u want to add to your list? ")
(def item (read-line))

(def mylist '())

(conj mylist item)

(println mylist))

This code gives me the below output user=> (load-file "core.clj") #'fun/-main user=> (fun/-main) Hello What do u want to add to your list? egg () nil user=>

Why is egg not added to my list

because clojure is a functional language, you can't "change" mylist. try (println (conj mylist item))

using def to hold changing values is not a good practice, btw. look for atom

Immutability..right :)

Need to get oop out of my head

😀

a quick example of what I mean

user=> (def item (atom nil))
#'user/item
user=> (reset! item (read-line))
Hi!
"Hi!"
user=> (def mylist [])
#'user/mylist
user=> (println (conj mylist @item))
[Hi!]
nil
user=> 

@suryapjr This is more of a imperative style of writing code. In term of statements; which inherently use state. I would suggest seeing https://www.infoq.com/presentations/Are-We-There-Yet-Rich-Hickey to get the whole Functional style of thinking. Would be helpful in learning Idiomatic Clojure and FP

Thanks !! @joelsanchez @rahul080327

For me seeing this before learning Clojure helped a lot 🙂

@rahul080327 thanks bud !!

what about def vs let

@joelsanchez..what is an atom

docs https://clojure.org/reference/atoms* examples https://clojuredocs.org/clojure.core/atom basically a reference to a value, which you can update in a thread-safe way ("atomically")

Hi again! When using cljsjs-packages, do I need to add their externs in the uberjar-profile in my luminus-project?

or is it automagic?

Hi everyone, is there a function or a library already exists to insert something on every nth entry in collection? Something like

(insert-nth 2 [1 2 3 4] "hello")
=> [1 2 "hello" 3 4 "hello"]

@hawari.rahman17

(let [n 2
      xs [1 2 3 4]
      in "hello"]
  (into []
        (comp (partition-all n)
              (mapcat #(conj % in)))
        xs))

That's way simpler than I come up with now, please let me digest that now @rauh

I've seen the documentation on into, I can't really understand what the xform part does? Could you explain it to me @rauh?

@hawari.rahman17 https://clojure.org/reference/transducers

Thanks @sundarj, I'll check it out

@hawari.rahman17 And if n is small you could get away with something like

(let [xs [1 2 3 4]] 
 (interleave (take-nth 2 xs) (take-nth 2 (rest xs)) (repeat "hello")))

@mfikes here's the 'alternative' version i came up with: (apply concat (interleave (partition 2 [1 2 3 4]) (repeat ["hello"])))

Yes, that is nice too @sundarj 🙂

It feels like interleave is fairly close to the original question, and when composed with partition you can arrive at a solution

yeah, though with partition-all you end up with an extra "hello" if the input is too long, and with partition you end up with the remainder being swallowed

suppose a butlast can be used in the partition-all case

@sundarj I just realized your solution can be golfed a litter further with flatten, which is getting pretty succinct 🙂

(flatten (interleave (partition 2 [1 2 3 4]) (repeat "hello")))

Summarizing, this solution is appealing because it is easy to read, while I bet the solution given by @rauh is much more efficient.

For a fair comparison with his solution:

(let [n 2
       xs [1 2 3 4]
       in "hello"]
  (flatten (interleave (partition n xs) (repeat in))))

simple-benchmark in Planck and Lumo show Rauh's running in 2/3 the time as the flatten approach in JavaScriptCore, but 3 times in V8. Hrm. I guess YMMV.

Hey peeps, I'm in the process of setting emacs up for Clojure. I'm coming from Dr.Racket and there new lines get automatically indented when inside brackets. In emacs not, unless I press tab or C-I.

@nikoszp There is probably a couple ways to handle parens. * paredit * parinfer are two that come to mind. I’m not sure how to autoformat in emacs off the top of my head.

@mfikes the one thing about flatten is that it doesn't respect your input datatype, in most cases it can be replaced with apply concat (which also will perform better) - or a cat transducer

or even mapcat

I've been fiddling with the "Clojure indent style" in the customization buffer but it doesn't seem to change anything. Thanks @drewverlee I'll have a look.

@nikoszp @drewverlee for making things indent properly, there's something like electric return that makes newline indent properly

I've had extremely poor experiences with co-workers abusing parinfer and I'd even advise counting parens by hand before considering parinfer

@noisesmith It's working! Thank you!!

How would I convert a sequence to a vector so I can call mapv on it? I tried this but it didnt work (mapv :a (into [] (-> checks (into {}))))

mapv returns a vector, it doesn't require one as input

(mapv inc (range 4)) == >[1 2 3 4]

note that (-> checks (into {})) is (into checks {}) which doesn't seem to do a lot of good

Thanks! I didnt notice that

play in the repl a lot. use doc and source. and run experiments on vectors like [:a :b :c]

I have what I think is a sequence of vectors of maps which I can’t figure out how to turn into a vector of maps

@josmith2016

user=> (reduce (partial reduce conj) [] '([{}] [{}]))
[{} {}]
user=> (into [] cat '([{}] [{}]))
[{} {}]

Thanks @sundarj! that worked

From this server:

(ns npuzzle.handler
  (:require [compojure.core :refer [GET POST defroutes]]
            [compojure.route :refer [resources]]
            [ring.util.response :refer [resource-response response not-found]]
            [ring.middleware.reload :refer [wrap-reload]]
            [ring.middleware.json :refer [wrap-json-response wrap-json-body wrap-json-params]]
            [ring.middleware.keyword-params :refer [wrap-keyword-params]]))

(defroutes routes
  (GET "/" [] (resource-response "index.html" {:root "public"}))
  (POST "/ajax/:params" [params] (println params))
  (resources "/"))

(def handler (-> #'routes wrap-json-response wrap-json-params (wrap-json-body {:keywords? true})))

I have values that will always be in one order. I'm looking to turn them into a map. This works (apply assoc (conj (interleave [:a :b] [1 2]) {})) but I'm betting there's something more idiomatic. Any suggestions?

(into {} (map vector [:a :b] [1 2])) - this is idiomatic, and performs better

I’d argue (zipmap [:a :b] [1 2]) is even more idiomatic because it’s purpose-built

i don't think that makes it more idiomatic.

> using, containing, or denoting expressions that are natural to a native speaker

the standard idiom is the one noisesmith posted above. or at least that's what i've seen the most and is easily recognized by me. others might vary. but i do think a standard pattern is more idiomatic than a function that does exactly what you are looking for

(-> thing :a :b) vs (get-in thing [:a :b]). one does exactly what you need. one is more general but seen quite a bit more i think

nah zipmap is more common

yeah I just forgot about zipmap (I rarely need it) so I just showed the pattern I use for stuff like that

agreed zipmap is common and the right thing to use

hey guys, quick help I’m trying to hook into repl :caught like that

(clojure.main/repl :caught (fn [t] (pprint t)))

for instance, could not find exit symbol

any idea why this is happening ?