⚠️ Under Heavy Development: This library is in active development and the API is not yet stable. Breaking changes may occur between releases. Not recommended for production use at this time.

Tapak is a web framework for OCaml 5, built on EIO (effect-based I/O).

📖 Read the full documentation

The OCaml ecosystem has several excellent web frameworks, each with different design philosophies:

• • Dream is stable but still evolving, it hasn't reached v1.0 yet.
• • Tiny_httpd looks stable, but I haven't used it personally.

With OCaml 5's effect handlers and EIO (effect-based I/O), we now have a foundation for writing concurrent code that is both ergonomic (direct style, no monads) and performant (no heap allocations for context switching).

Tapak explores what a modern, practical web framework looks like when built on this foundation.

This is an experiment in pushing the boundaries of typed functional web development while keeping pragmatism and real-world usage in mind.

Since Tapak is still in development and the API is being designed, it's not yet published to Opam. You can still install it using one of the following methods:

Pin the repository directly from GitHub:

# Pin from the main branch
opam pin add tapak https://github.com/syaiful6/tapak.git

# Or pin from a specific branch
opam pin add tapak https://github.com/syaiful6/tapak.git#branch-name

# Install dependencies and build
opam install tapak --deps-only

Add Tapak as a flake input in your flake.nix:

{
  inputs = {
    tapak.url = "github:syaiful6/tapak";
    # Or specify a branch:
    # tapak.url = "github:syaiful6/tapak/main";
  };

  outputs = { self, tapak, ... }: {
    # Use tapak in your development environment or package build
    # you know how to do this, you use nix btw.
  };
}

Here's a simple example demonstrating type-safe routing, middleware composition, and EIO integration:

open Tapak

let home_handler _req =
  Response.of_html ~status:`OK
    "<h1>Welcome to Tapak!</h1>"

let user_handler user_id _req =
  (* user_id is automatically parsed as int64 *)
  let html = Printf.sprintf "<h1>User %Ld</h1>" user_id in
  Response.of_html ~status:`OK html

let api_handler id name _req =
  (* Both id (int64) and name (string) are type-safe *)
  let json =
    Printf.sprintf {|{"user_id": %Ld, "name": "%s"}|} id name
  in
  Response.of_string ~status:`OK json

let app env =
  let open Middleware in
  let open Router in
  App.(
    routes
      [ get (s "") |> into home_handler
      ; get (s "users" / int64) |> into user_handler
      ; get (s "api" / s "users" / int64 / str) |> into api_handler
      ]
      ()
    <++> [ use (module Request_logger)
             (Request_logger.args
               ~now:(fun () -> Eio.Time.now (Eio.Stdenv.clock env))
               ())
         ])

let () =
  Eio_main.run @@ fun env ->
  let port = 3000 in
  let address = `Tcp (Eio.Net.Ipaddr.V4.any, port) in
  let config = Piaf.Server.Config.create address in
  Printf.printf "Server running on http://localhost:%d\n" port;
  ignore (Server.run_with ~config ~env (app env))

For more examples, see the examples/ directory.