Lean into JavaScript

• 01

  All the power of Lean

  LeanScript picks up where the Lean compiler leaves off, so your code is checked and optimized just as it is for a native build. Dependent types, proofs, and macros all work, and proofs are erased before any JavaScript is emitted.

• 02

  Coming soon

• 03

  Coming soon

• 04

  Coming soon

Deploy your Lean code to Cloudflare's global edge network with Cloudflare Workers.

import Js

open Std.Async
open Js.Fetch

/-- Responds to `req` with a greeting, echoing the body of a `POST` request. -/
def handle (req : Request) : Async Response := do
  let body ←
    if req.method == "POST" then
      pure s!"Hello from Lean! You sent: {← req.text}\n"
    else
      pure s!"Hello from Lean! You requested {req.url}\n"
  Response.new body { headers := #[("Content-Type", "text/plain; charset=utf-8")] }

/-- The Worker's `fetch` handler. -/
@[export default.fetch]
def fetch (req : Request) (_env _ctx : JsValue) : BaseIO JsValue :=
  JsValue.ofAsync (handle req)

LeanScript fits into your existing Lean project and JavaScript package manager.

1. 1Require LeanScript in your Lake package

   lakefile.toml

   [[require]]
   name = "leanscript"
   git = "https://github.com/maxdeviant/leanscript"
   rev = "v0.1.0"

2. 2Install the Vite plugin

   Terminal

   pnpm add -D @leanscript/vite-plugin@0.1.0 vite

3. 3Add the plugin to your Vite config

   vite.config.js

   import { defineConfig } from "vite";
   import leanscript from "@leanscript/vite-plugin";
   
   export default defineConfig({
     plugins: [leanscript()],
   });

4. 4Load a Lean file on your page

   index.html

   <!doctype html>
   <html lang="en">
     <head>
       <meta charset="utf-8" />
       <title>My app</title>
     </head>
     <body>
       <div id="app"></div>
       <script type="module" src="./Main.lean"></script>
     </body>
   </html>

5. 5Write some Lean

   Main.lean

   import Js
   
   open Js.Dom
   
   def main : IO Unit := do
     let some app ← (← document).getElementById "app" | return
     app.setTextContent "Hello from Lean!"

Check out the leanscript-template-web repository for a full example.