clojure.core/ns

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Type: macro Added: Clojure 1.0 Examples: 13 Runnable: 3

([name docstring? attr-map? references*])

Sets ns to the namespace named by name (unevaluated), creating it if needed. references can be zero or more of: (:refer-clojure ...) (:require ...) (:use ...) (:import ...) (:load ...) (:gen-class) with the syntax of refer-clojure/require/use/import/load/gen-class respectively, except the arguments are unevaluated and need not be quoted. (:gen-class ...), when supplied, defaults to :name corresponding to the ns name, :main true, :impl-ns same as ns, and :init-impl-ns true. All options of gen-class are supported. The :gen-class directive is ignored when not compiling. If :gen-class is not supplied, when compiled only an nsname__init.class will be generated. If :refer-clojure is not used, a default (refer 'clojure.core) is used. Use of ns is preferred to individual calls to in-ns/require/use/import:

(ns foo.bar (:refer-clojure :exclude [ancestors printf]) (:require (clojure.contrib sql combinatorics)) (:use (my.lib this that)) (:import (java.util Date Timer Random) (java.sql Connection Statement)))

Examples

by devijvers on 2010-07-14 . May have evaluation errors. ▶

;; Generate a Java class (ns org.clojuredocs.test (:gen-class)) (defn -main [] (println "Hello, World!")) ;; After compilation: sh$ java -cp classes org.clojuredocs.test Hello, World!

by belun on 2010-09-20 . May have evaluation errors. ▶

;; Let's create a namespace and then assign it as the current namespace (create-ns 'my-new-namespace) #namespace[my-new-namespace] (ns 'my-new-namespace) java.lang.ClassCastException: clojure.lang.PersistentList cannot be cast to clojure.lang.Symbol (NO_SOURCE_FILE:26) ;; oops, this is not the way to do it; if create-ns needs a symbol, ns does not (ns my-new-namespace) nil ;; it worked as the current namespace is our newly created one

by belun on 2010-09-21 . May have evaluation errors. ▶

;; Generating a class so we can call Clojure from Java (ns com.domain.tiny (:gen-class :name com.domain.tiny :methods [#^{:static true} [binomial [int int] double]])) (defn binomial "Calculate the binomial coefficient." [n k] (let [a (inc n)] (loop [b 1 c 1] (if (> b k) c (recur (inc b) (* (/ (- a b) b) c)))))) (defn -binomial "A Java-callable wrapper around the 'binomial' function." [n k] (binomial n k)) (defn -main [] (println (str "(binomial 5 3): " (binomial 5 3))) (println (str "(binomial 10042 111): " (binomial 10042 111)))) ;; Calling from Java import com.domain.tiny; public class Main { public static void main(String[] args) { System.out.println("(binomial 5 3): " + tiny.binomial(5, 3)); System.out.println("(binomial 10042, 111): " + tiny.binomial(10042, 111)); } } ;; The result was: (binomial 5 3): 10.0 (binomial 10042, 111): 4.9068389575068143E263 ;; Example was borrowed from clartaq @ Stack Overflow

by remleduff on 2010-11-05 ▶

;; Create a namespace named demo.namespace. (ns demo.namespace) ;; Clojure recommends namespaces be at least "two segments" (ie, they should ;; have at least one '.') otherwise it will create a class in the "default ;; package", which is discouraged. ;; If this declaration appears in a file named "demo/namespace.clj" present ;; in your classpath, it is known as a "lib", "demo/namespace.clj" is the lib's ;; "root resource". See http://clojure.org/libs ;; From a clean repl you can load the lib using (require 'demo.namespace) ; or (use 'demo.namespace)

by remleduff on 2010-11-05 . May have evaluation errors. ▶

;; This example will illustrate changing between namespaces at the repl ;; At the repl, the ns macro can be used to create a namespace, but it is ;; used to change the current namespace (be careful of typos) (ns demo.namespace) nil ; The prompt at the repl is now "demo.namespace" reflecting ; that the current namespace is no longer "user". ;; Add a new function to demo.namespace (defn foo [] (prn "Hello from demo.namespace")) #'demo.namespace/foo ;; From within "demo.namespace" we can use foo without qualifying it (foo) "Hello from demo.namespace" nil ;; Switch back to the "user" namespace (ns user) nil ;; We can no longer use "foo" without qualification (foo) java.lang.Exception: Unable to resolve symbol: foo in this context (NO_SOURCE_FILE:4) (demo.namespace/foo) "Hello from demo.namespace" nil ;; The public symbols of "demo.namespace" can be "referred into" the "user" ;; namespace if desired (refer 'demo.namespace) nil ;; foo is now an alias in the "user" namespace which refers to the ;; "demo.namespace/foo" symbol (foo) "Hello from demo.namespace" nil

by boxie on 2010-11-10 . May have evaluation errors. ▶

(ns rosettacode.24game (:require [clojure.string :as str]) (:use clojure.test)) (deftest test (is (= "ABC" (str/capitalize "abc")))

by scode on 2011-02-14 . May have evaluation errors. ▶

;; Multiple required namespaces with aliases (ns demo.namespace (:require [com.example.httplib :as httplib] [com.example.otherlib :as otherlib]))

by gstamp on 2012-06-26 . May have evaluation errors. ▶

;; In clojure 1.4 and higher you can use the refer function from within ;; a require which is equivalent to (:use foo only [...]) but still ;; allows you to reference the required namespace: (ns my.ns.example (:require [my.lib :refer [function1 function2]])) ;; And :refer :all is equivalent to :use : (ns my.ns.example (:require [my.lib :refer :all]))

by devn on 2013-01-20 . May have evaluation errors. ▶

(ns foo.bar (:refer-clojure :exclude [ancestors printf]) (:require [clojure.contrib sql sql.tests]) (:use [my.lib this that]) (:import [java.util Date Timer Random] (java.sql Connection Statement)))

by PetrGlad on 2016-09-06 . May have evaluation errors. ▶

; Gotchas (ns newns1 [:require clojure.string]) ; newns1=> nil ; Success ; Note use of vector instead of list - ns macro successfuly processes it ; but some tools that read this code might not recognize this dependency. ; Always write ns as per documentation. (in-ns 'newns2) ; newns2=> #object[clojure.lang.Namespace 0x29a8c1fb "newns2"] ; New namespace was successfully created (first []) ; newns2=> CompilerException java.lang.RuntimeException: ; Unable to resolve symbol: first in this context, ; compiling:(NO_SOURCE_PATH:7:1) ; Although "first" is in core library, it's name is not available here. ; To fix this do (clojure.core/refer-clojure) ; newns2=> nil (first []) ; newns2=> nil ; Success ; "ns" macro both switches to a namespace and refers default library, ; "in-ns" just switches to given namespace (ns newns3) ; newns3=> nil (first []) ; newns3=> nil

by thescalaguy on 2017-10-23 . May have evaluation errors. ▶

;; Shows how to use an attr-map ;; These are arbitrary key-value pairs (ns cljdocs.example.core "This is a doc string, FYI :D" {:author "John Doe" :last-update-date "23-10-2017"}) => nil ;; The keys in the attr-map are merged with the compiler-generated attr-map (meta *ns*) => {:doc "This is a doc string, FYI :D", :author "John Doe", :last-update-date "23-10-2017"}

by mars0i on 2019-02-09 ▶

;; If you import a Java class with an unqualified name (perhaps from local ;; source file), use the bare class name without placing it in a vector or list: (ns foo.bar (:import MyClass))

by green-coder on 2020-11-06 ▶

;; References to things in a given namespace can be locally renamed. (ns foo.bar (:require [clojure.string :refer [blank?] :rename {blank? contains-only-spaces-likes?}])) (contains-only-spaces-likes? " ") ; => true

Note by gstamp

Good description of use/require/import here:

http://blog.8thlight.com/articles/2010/12/6/clojure-libs-and-namespaces-require-use-import-and-ns

Note by finalfantasia

How to ns -- Stuart Sierra’s Opinionated Style Guide for Clojure Namespace Declarations

Make it look like this:

(ns com.example.my-application.server
  "Example application HTTP server and routing."
  (:refer-clojure :exclude [send])
  (:require
   [clojure.core.async :as async :refer [<! <!! >! >!!]]
   [com.example.my-application.base]
   [com.example.my-application.server.sse :as server.sse]
   [io.pedestal.http :as http]
   [io.pedestal.http.sse :as http.sse]
   [ring.util.response :as response])
  (:import
   (java.nio.file Files LinkOption)
   (org.apache.commons.io FileUtils)))

Note by matasaru

The post referred in the first note has moved to:

https://8thlight.com/insights/clojure-libs-and-namespaces-require-use-import-and-ns

See also

• clojure.core/use (1)
• clojure.core/require (4)
• clojure.core/refer (1)
• clojure.core/import (2)
• clojure.core/ns-publics (1)
• clojure.core/in-ns (0)
• clojure.core/remove-ns (0)
• clojure.core/ns-map (1)
• clojure.core/*ns* (0)
• clojure.core/alias (2)

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