jphedley/example-servant-elm

Example for a web app with a servant backend and an elm frontend

Haskell Servant and Elm Example

This example project illustrates how to set up a project that:

• Uses haskell and servant as a backend exposing a JSON api (and serving some files).
• Uses elm to write the frontend.
• Uses servant-elm to generate client functions in elm for the JSON api. This means that mismatches regarding the JSON api will be detected statically.
• Allows a very fast development cycle: You can type-check the server and client code in a very short amount of time.

Makefile

There's a Makefile included with the following targets:

• setup -- Set up everything: install ghc and dependencies. (Needs stack, elm and elm-test.)
• build -- Build the server and the client.
• server-start -- Start the server here: http://localhost:3000/. Requests sent to this server will trigger a recompilation of the client code (not the server code).
• server-start-reserve -- Start reserve to serve the app on http://localhost:12000/. In this setting, both changes to the client and server code will be automatically triggered by http requests. This is the ideal mode for running the app during compilation, however it has some caveats:
  • reserve crashes from time to time. Don't know why.
  • Currently the server has an in-memory fake database. Since reserve restarts the server for every request, nothing is persistant. (We should switch to a real database for this example.)
• sensei-start -- Starts sensei. Needed for fast-test.
• fast-test -- Recompiles the client and server code. And runs the test-suite. Meant to be run often after making changes to the code during development.

Caveats

• This project uses https://travis-ci.org/soenkehahn/wai-make-assets, which is experimental. E.g. there's no support for serving the assets in a production setting.