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A Lisp on the JVM
(print) to print for humans(println) to print with newline for humans(pr) to print for data(prn) to print with newline for data(+ 1 1)2
(range 5)(0 1 2 3 4)
(range 5 10)(5 6 7 8 9)
(range 10 20 2)(10 12 14 16 18)
"Damien"Damien
(apply str (reverse "Damien"))neimaD
(def name "Damien")
(str "Hello " name)Hello Damien
(clojure.string/join ", " ["element 1" "element 2" "element 3"])element 1, element 2, element 3
(clojure.string/includes? "Damien" "en")true
Clojure characters are Java characters
\a| special character | result |
|---|---|
\newline | "\n" |
\space | " " |
\tab | "\t" |
\formfeed | "\f" |
\backspace | "\b" |
\return | "\r" |
Keywords are symbolic identifiers that evaluate to themselves.
Example:
:foo(keyword 'foo):foo
(keyword "foo"):foo
(keyword? :foo)true
(keyword? "foo")false
(def x 42)
x42
defoncedefonce defines variable only if it has never been defined before:
(defonce y 9)
y9
If you try to re-define it, it won't work:
(defonce y 10)
y9
(let [[a b c] '(1 2 3)] (println a b c))1 2 3
Check if something is nil:
(nil? nil)true
Check if something is NOT nil:
(some? nil)false
(some? 1)let can be used to define a variable in a specific scope:
(let [z 5] z)5
z is not defined outside of the scope:
zclass clojure.lang.Compiler$CompilerException
"defn" = "def" + "fn" (define function)
(defn greet [name] (str "Hello, " name))
(greet "Damien")Hello, Damien
Which is syntactic sugar for:
(def greet (fn [name] (str "Hello, " name)))
(greet "Damien")Hello, Damien
(defn greet
([] (greet "World!"))
([name] (str "Hello, " name)))
(println (greet "Damien"))
(println (greet))Hello, Damien
Hello, World!
#() with % used as arguments (%1, %2 for first and second arguments)
(map #(* 2 %) '(1 2 3))(2 4 6)
Which is syntactic sugar for:
(map (fn [x] (* 2 x)) '(1 2 3))(2 4 6)
All Clojure collections are immutable and persistent.
'(1 2 3)(1 2 3)
Which is syntactic sugar for:
(list 1 2 3)(1 2 3)
(first '(1 2 3))1
(last '(1 2 3))3
(count '(1 2 3))3
(take 2 '(1 2 3 4))(1 2)
Take Last
(take-last 2 '(1 2 3 4))(3 4)
(some #(= 3 %) '(1 2 3))true
(some) alone only returns nil, not false
(some? (some #(= 4 %) '(1 2 3)))false
(frequencies '("a" "b" "b" "c" "c" "c")){"a" 1, "b" 2, "c" 3}
(sort '(2 3 1))(1 2 3)
(remove #{"the" "a" "ate"} '("the" "monkey" "ate" "a" "banana"))("monkey" "banana")
[1 2 3][1 2 3]
Which is syntactic sugar for:
(vector 1 2 3)[1 2 3]
Collections of unique values.
#{1 2 3}#{1 3 2}
Which is syntactic sugar for:
(set [1 2 3])#{1 3 2}
Can be used to remove duplicates from a vector:
(set [1 2 3 1 2 3])#{1 3 2}
{:a 1, :b 2}{:a 1, :b 2}
Which is syntactic sugar for:
(hash-map :a 1, :b 2){:b 2, :a 1}
Comma is actually not required:
{:a 1 :b 2}{:a 1, :b 2}
(get {:a 1 :b 2} :a)1
"get" can be omitted
({:a 1 :b 2} :b)2
(get-in {:error {:code 404 :message "Wrong location"}} [:error :code])404
(if true "this is true" "this is false")this is true
(if false "this is true" "this is false")this is false
Only handles "true", and wrapped in an implicit (do) statement
(when true (println "this is true") (println "this is also true"))this is true
this is also true
(def x 10)
(cond (= x 10) "true")true
Note: for this type of conds, if the first is true, it won't continue
(def x (rand-int 50))
(cond
(> x 40) "more than 40"
(> x 30) "more than 30"
(> x 20) "more than 20"
(> x 10) "more than 10"
:else "neither")more than 30
Another example
(def x (rand-int 50))
(cond
(> x 40) "more than 40"
(> x 30) "more than 30"
(> x 20) "more than 20"
(> x 10) "more than 10"
:else "neither")neither
(let [name "Damien"]
(case name
"Damien" "my real name"
"Jane" "my neighbour's name"
"John" "my colleague's name"))my real name
(let [name "Jane"]
(case name
"Damien" "my real name"
"Jane" "my neighbour's name"
"John" "my colleague's name"))my neighbour's name
Can provide a default:
(let [name "Hugo"]
(case name
"Damien" "my real name"
"Jane" "my neighbour's name"
"John" "my colleague's name"
"Unknown name"))Unknown name
Can "match" multiple values using a list:
(let [name "Jane"]
(case name
("Damien" "Jane" "John") "an acquaintance"
"not an acquaitance"))an acquaintance
(map #(* 3 %) '(1 2 3))(3 6 9)
(reduce + '(3 3 3))9
(filter odd? (range 10))(1 3 5 7 9)
equality of the data.(pprint (meta #'+)){:added "1.2",
:ns #namespace[clojure.core],
:name +,
:file "clojure/core.clj",
:inline-arities #function[clojure.core/>1?],
:column 1,
:line 986,
:arglists ([] [x] [x y] [x y & more]),
:doc
"Returns the sum of nums. (+) returns 0. Does not auto-promote\n longs, will throw on overflow. See also: +'",
:inline #function[clojure.core/nary-inline/fn--5606]}
(def m ^:hi [1 2 3])
(meta (with-meta m {:bye true})){:bye true}
(require '[clojure.string :as str])(str/split (str/upper-case "a b c") #" ")["A" "B" "C"]
Becomes
(-> "a b c" (str/upper-case) (str/split #" "))["A" "B" "C"]
Insert as last argument
(->> (range 10) (filter odd?))(1 3 5 7 9)
Write to file:
(spit "blob.txt" "toast")nil
Read from file:
(slurp "blob.txt")toast
Can be used over HTTP:
(slurp "https://dummyjson.com/quotes/1"){"id":1,"quote":"Life isn’t about getting and having, it’s about giving and being.","author":"Kevin Kruse"}
https://lwhorton.github.io/2018/10/20/clojurescript-interop-with-javascript.html
https://google.github.io/closure-library/api/
https://github.com/babashka/nbb
Babahska for ClojureScript / Node.js
https://github.com/babashka/scittle
The Small Clojure Interpreter exposed for usage in browser script tags
https://github.com/thheller/shadow-cljs
ClojureScript compilation made easy
https://github.com/clj-commons/secretary
A client-side router for ClojureScript
https://github.com/squint-cljs/cherry
Experimental ClojureScript to ES6 module compiler
https://github.com/squint-cljs/squint
ClojureScript syntax to JavaScript compiler
https://www.youtube.com/playlist?list=PLUGfdBfjve9VGzp7G1C9FYfH8Yk1Px-11
https://github.com/babashka/babashka
Native, fast starting Clojure interpreter for scripting
https://github.com/clj-kondo/clj-kondo
A linter for Clojure code that sparks joy.
The Fullest Full Stack Clojure Web Framework
https://github.com/weavejester/hiccup
Fast library for rendering HTML in Clojure
https://github.com/Tensegritics/ClojureDart
A port of Clojure that compiles to Dart (mostly for Flutter framework)
https://github.com/tonsky/datascript
Immutable database and Datalog query engine for Clojure, ClojureScript and JS
https://github.com/borkdude/quickdoc
Quick and minimal API doc generation for Clojure
Pedestal is a set of libraries that we use to build services and applications. It runs in the back end and can serve up whole HTML pages or handle API requests.
https://github.com/djblue/portal
A clojure tool to navigate through your data.
Automate Clojure projects without setting your hair on fire.
https://github.com/babashka/neil
A CLI to add common aliases and features to deps.edn-based projects.
https://github.com/vouch-opensource/krell
Simple ClojureScript React Native Tooling
https://kimh.github.io/clojure-by-example/
https://lambdaisland.com/episodes/list-comprehension-clojure-for
https://lambdaisland.com/episodes/clojure-seq-seqable
https://lambdaisland.com/episodes/javascript-libraries-clojurescript
https://lambdaisland.com/episodes/clojure-keyword-arguments
https://lambdaisland.com/episodes/clojurescript-interop