Mig - library to write composable and lightweight servers

The Mig is a library to build lightweight composable servers. The main strength is ability to build servers from parts and flexible and type-safe DSL which features only small amount of functions. The name mig (pronounced as meeg) is a russian word for "instant moment".

Hello world server example

With the library mig-server installed we can define a simple server with two routes:

{-# Language OverloadedStrings #-}

import Mig.Json.IO

-- | Starts server on port 8085.
main :: IO ()
main = runServer 8085 (withSwagger def server)

-- | The server definition
server :: Server IO
server = 
  "api/v1" /. 
    [ "hello" /. hello
    , "bye" /. bye
    ]

-- | The handler definition as a function
hello :: Get (Resp Text)
hello = pure $ ok "Hello World"

-- | The handler definition as a function with a query parameter to ask for the user name
bye :: Query "user" Text -> Get (Resp Text)
bye (Query name) = pure $ ok ("Goodbye " <> name)

We can test the server with curl or with swagger-ui if it's run localy on the url http://localhost:8085/swagger-ui. For more examples see the directory.

Comparison to Scotty and Servant

I like scotty for being very simple and servant for being composable, type-safe and how functions are used as handlers which provides decoupling of Web-handlers from application logic. But sometimes scotty feels too imperative and lacks servant's composability. And servant with type-level magic and huge errors can feel to complicated. So I wanted to create something in the middle. Something composable and simple at the same time.

Structure of the repo

An overview of the mig repo:

• mig - core library. It defines DSL and low-level represenatation for API and server as a function

• mig-wai - conversion of mig servers to WAI applications

• mig-extra - extra utils for core library

• mig-swagger-ui - swagger servers for mig servers. Offers nice in the browser UI to test HTTP REST applications

• mig-server - mig servers based on warp with batteries included

• mig-rio - binding to rio library. It comtains instance of the HasServer class for RIO type.

• examples - several examples of servers and clients. Examples can be run with commands in the Makefile of their subdirectory.

• docs - tutorial for the library and reference of the main functions. It is build with mdbook and deployed on github pages.

See Makefile for main commands to work with repo in dev mode.

Tutorial and other links

• Quick start guide: tutorial
• Summary of the main functions: refs
• How to contribute: guide
• Examples: examples directory