The Publics Good

tl;dr ns-publics gives you a list of the the public vars in a Clojure namespace.

When I was writing up my quick note on mapv, I wanted to flesh it out by looking for similar functions in clojure.core. I’ve never really needed to introspect a Clojure namespace like that before, so I started with a web search. That turned up the ns-publics function, which, as it says on the tin, returns all the public vars in the given namespace. Specifically, it returns a map whose keys are symbols, and whose values are the interned vars.¹

user=> (in-ns 'foo)
#object[clojure.lang.Namespace 0x66b72664 "foo"]
foo=> (clojure.core/ns-publics 'foo)
{}
foo=> (def bar "BAR!")
#'foo/bar
foo=> (def ^:private baz "BAZ!")
#'foo/baz
foo=> (clojure.core/ns-publics 'foo)
{bar #'foo/bar}

Groovy. So for my use case (finding mapv and its relatives) all I have to do is this:

(->> (ns-publics 'clojure.core)
     keys
     (filter #(clojure.string/ends-with? % "v")))

(filterv reduce-kv mapv)

Since reduce-kv is something else entirely, it looks like mapv and filterv are the vector-producing siblings. (As reported in that earlier post. 😀)

And speaking of related functions, ns-publics has its share of kin:

• ns-interns is a map of all the vars, whether public or private. (A superset of ns-publics.)
• ns-aliases is a map of all the aliased namespaces in a namespace. That is, (require '[clojure.string :as str]) would cause ns-aliases to produce a map including {str #object[clojure.lang.Namespace 0x35c09b94 "clojure.string"]}.
• ns-refers is a map of all the function references in a namespace. That is, (require '[clojure.string :refer [ends-with?]]) would cause ns-refers would produce a map including {ends-with? #'clojure.string/ends-with?}.
• ns-imports is a map of all the Java imports in a namespace. That is, (import '[java.util Base64]) would cause ns-imports to produce a map including {Base64 java.util.Base64}.
• ns-map is a big ol’ map that’s essentially (merge (ns-interns *ns*) (ns-imports *ns) (ns-refers *ns*)). (So it doesn’t include ns-aliases.)

It’s nifty, though not surprising, that Clojure has mechanisms for getting at this information. It’s always fun to get a chance to explore another corner of the language.

Questions? Comments? Contact me!