A prototype of a compiler from Clojure to Swift.

I enjoy programming in Clojure. Its value orientation, dynamism, and simplicity enable a level of power and flexibility that many other programming languages, including Swift, cannot provide. This got me thinking, 'Can I use Clojure to program iOS apps?.' There is ClojureScript, which, in combination with React Native, can be used to build iOS apps.¹ However, with React Native, you still don't have direct access to the platform's native APIs, and, as a result, you still need to use Swift sometimes. So, I decided to see if I could compile Clojure to Swift. It would also be a great way to learn more about Clojure and compilers, and to have some fun :).

At a high level, the Clojure compiler can be broken down into the following components:

reader -> analyzer -> emitter

• The reader reads Clojure text and transforms it into Clojure data structures.
• The analyzer analyzes the Clojure data and enriches it, outputting an AST.
• The emitter walks the AST and emits the target code. In the case of Clojure, the emitter emits JVM bytecode; in the case of ClojureScript, JavaScript code; and in the case of ClojureSwift, Swift code.

Fortunately, the Clojure compiler is very modular. ClojureSwift reuses the reader and tools.analyzer, which is a host-agnostic analyzer for Clojure code. On top of it, it provides tools.analyzer.swift for Swift-specific analysis, and a Swift-specific emitter.

Ultimately, the idea is that the emitter would automatically feed into the Swift compiler, which would then compile the Swift code down to native code.

As said above, this is a prototype. It's nowhere near production-ready; however, it demonstrates the ability to compile certain Clojure forms for Swift. For instance:

(def id #uuid "1369709c-2bdc-4e35-9ae1-1cde9068f672")

is compiled to:

var id = Foundation.UUID(uuidString: "1369709c-2bdc-4e35-9ae1-1cde9068f672")!

To run the tests:

clj -X:test:test/run