Platform-independent math functions in Clojure(script)

Question

How to access things like sin, cos or PI in a pure Clojure way?

For example, if I want to write a pure library, I mustn’t use anything like (.PI Math) (Java) or (.‑PI js/Math) (JS).

Littlejohn

The "pure Clojure way" is to use interop with the host language when appropriate, as in this case. Are you asking (a) whether there is a host-language-neutral math library or (b) how to write code for both Clojure and ClojureScript? If the latter, have a look at github.com/lynaghk/cljx. – Boyne

Answer 1

The easiest way is to use Cljx: https://github.com/lynaghk/cljx

With it you can write something like:

(* 5 #+clj (.PI Math) #+cljs (.‑PI js/Math))

and have this code compiled properly to Clojure and ClojureScript.

As far as I know there’s no better way to write one code to be runned as Clojure/ClojureScript.

There are some plans to include platform detection in Clojure itself but I think it’s not ready yet.

Pinkiepinkish

I got some weird characters copying and pasting the js interop for Math/PI here, might be worth typing it yourself. Good answer though, thanks. – Interfile

Answer 2

Official wrapper APIs: clojure.math & cljs.math

For simple constants or common mathematical functions, the first thing I'd reach for (other than interop) would be the clojure.math and cljs.math libs, which provide cljs.math/PI, clojure.math/sin, and so on.

Cljx

Another answer suggests Cljx, which has been deprecated for a few years. See the transition guide, which is also a good overview of the new solution:

.cljc

Code targeting multiple Clojure platforms is written in .cljc files using reader conditionals (introduced in Clojure 1.7).

The excellent kixi.stats implements platform-independent Clojure math using cljc, providing us not only a useful library but also a nice example of the approach. An excerpt:

(def PI
  #?(:clj Math/PI
     :cljs js/Math.PI))

(defn sin [x]
  #?(:clj  (Math/sin x)
     :cljs (js/Math.sin x)))

(def infinity
  #?(:clj Double/POSITIVE_INFINITY
     :cljs js/Infinity))

This code is from kixi.stats.math.

Scarborough

Answer 3

Sin example:

(.sin js/Math 3) 

PI example:

(aget js/Math "PI")

Displaying in console:

(.log js/console (aget js/Math "PI"))

Hope that helps.

Headboard

How is that platform independent ? – Kellda

Hi,Please read the title (I.E. it states "Clojurescript" :) The term "platform independent" is not definitive. Generally speaking, javascript is considered "platform independent" (as in, most modern OS's support standard jsvascript). The javascript Math library is standard. Thus, I would need to ask what platforms are you concerned about that don't support javascript? More importantly, why are you using Clojurescript on a platform that doesn't include standard javascript? – Headboard

Did you even read the question? Platform in this case is the implementation of Clojure of course. You just showed how to do it on the Javascript platform (which I did in the question already, btw.). – Littlejohn

Hi, Please edit the question so that includes your definition of "platform". Please edit the title :) Folks can only answer the question you ask:) The more specific your question, the less ambiguities, the better the answers :) Good Luck :) – Headboard

IMHO it’s pretty clear from the question. yonki seems to think that, too, because his answer relates to the right thing. – Littlejohn

Thanks for leaving the answer in here, it helped me. – Ancestor