A Swift library to write Emacs plugins in Swift!


Emacs Swift module provides a convenient API for writing dynamic modules for Emacs in Swift. It marries a dynamic nature of Emacs Lisp with strong static typization of Swift and hides the roughness of the original C API together with harder aspects of that language such as a lack closures and manual memory management. It also translates Emacs Lisp errors and Swift exceptions into each other.

A Quick Tour

EmacsSwiftModule allows you to call functions from Emacs Lisp using Swift’s own types.

let two: Int = try env.funcall("+", with: 1, 1)
assert(two == 2)
try env.funcall("message", with: "%S %S", "Hello", 42)

And define your own Lisp functions out of Swift closures

try env.defun("foo") {
  (x: Int, y: Int) in x + y
try env.defun("bar") {
  (input: [String]) in input.joined(separator: ", ")

that can be easily used in Emacs Lisp

(foo 1 1) ;; => 2
(bar ["Hello" "World"]) ;; => "Hello, World"

It handles errors on both sides so the user can almost always simply ignore them.

try env.defun("always-throws") { (x: Int) throws in
  throw MyError(x: x)
try env.defun("calls-afdsiufs") {
  (env: Environment) in
  do {
    try env.funcall("afdsiufs", with: 42)
  } catch EmacsError.signal {
    print("Whoops! It looks like 'afdsiufs' doesn't exist!")

And on the Lisp side too

(always-throws 42) ;; => raises (swift-error "Swift exception: MyError(x: 42)")
(calls-afdsiufs) ;; => nil because we caught the error

The same happens when a type requirement expected in Swift is not met.

(foo "Hello" "World") ;; => raises (wrong-type-argument numberp "Hello")


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