A tasty Haskell front-end framework

Miso Slack Hackage Haskell Hackage LICENSE appveyor Miso Hydra IRC #haskell-miso

Miso is a small "isomorphic" Haskell front-end framework for quickly building highly interactive single-page web applications. It features a virtual-dom, diffing / patching algorithm, attribute and property normalization, event delegation, event batching, SVG, Server-sent events, Websockets, type-safe servant-style routing and an extensible Subscription-based subsystem. Inspired by Elm, Redux and Bobril. Miso is pure by default, but side effects (like XHR) can be introduced into the system via the Effect data type. Miso makes heavy use of the GHCJS FFI and therefore has minimal dependencies.

Table of Contents

Quick start

To get started quickly building applications, we recommend using the stack or nix package managers. Obtaining GHCJS is required as a prerequisite. stack and nix make this process easy, if you're using cabal we assume you have obtained GHCJS by other means.

All source code depicted below for the quick start app is available here.


In the miso repository there is a folder named stack with "known to work" configurations for GHCJS. One stack file exists for both the 7.10.3 and 8.0.1 versions of GHCJS. In general, we recommend developing with the 7.10.3 version since it currently supports GHCJSi (a REPL that connects to the browser by way of a nodejs web server using socket.io) and building with the 8.0.1 version (if possible). For more information on using stack with GHCJS, please consult the GHCJS section of the stack docs.

To begin, create the following directory layout

➜  mkdir app && touch app/{Main.hs,app.cabal,stack.yaml} && tree app
|-- Main.hs
|-- app.cabal
`-- stack.yaml

Add a stack.yaml file that uses a recent version of miso.

➜  cat app/stack.yaml
resolver: lts-6.20
compiler: ghcjs-
compiler-check: match-exact

 - '.'
 - miso-

         url: http://ghcjs.tolysz.org/lts-6.20-9006020.tar.gz
         sha1: a6cea90cd8121eee3afb201183c6e9bd6bacd94a

Add a cabal file

➜  cat app/*.cabal
name:                app
synopsis:            First miso app
category:            Web
build-type:          Simple
cabal-version:       >=1.10

executable app
  main-is:             Main.hs
  build-depends:       base, miso
  default-language:    Haskell2010

Add the source from Sample Application to app/Main.hs

Run stack setup. This might take a long time, since it will have to build GHCJS.

stack setup

Run stack build to get the static assets

stack build

See the result

open $(stack path --local-install-root)/bin/app.jsexe/index.html

Using GHCJSi

stack ghci

If that warns with socket.io not found, browser session not available, you'll need to install socket.io

npm install socket.io

and update your NODE_PATH

export NODE_PATH=$(pwd)/node_modules

Now you should be connected, and the app viewable in GHCJSi (open http://localhost:6400).

➜  stack ghci
app- initial-build-steps (exe)
Configuring GHCi with the following packages: app
GHCJSi, version http://www.github.com/ghcjs/ghcjs/  :? for help
[1 of 1] Compiling Main             ( /Users/david/Desktop/miso/sample-app/Main.hs, interpreted )
socket.io found, browser session available at http://localhost:6400
Ok, modules loaded: Main.
*Main> main
browser connected, code runs in browser from now on


Nix is a more powerful option for building web applications with miso since it encompasses development workflow, configuration management, and deployment. The source code for haskell-miso.org is an example of this.

If unfamiliar with nix, we recommend @Gabriel439's "Nix and Haskell in production" guide.

To get started, we will use the cabal2nix tool to convert our Cabal file into a nix derivation (named app.nix). We'll then write a file named default.nix, which is used for building our project (via nix-build) and development (via nix-shell).

To begin, make the following directory layout:

➜  mkdir app && touch app/{Main.hs,app.cabal,default.nix,app.nix} && tree app
|-- Main.hs
|-- app.cabal
|-- default.nix
`-- app.nix

Add a cabal file

➜  cat app/*.cabal
name:                app
synopsis:            First miso app
category:            Web
build-type:          Simple
cabal-version:       >=1.10

executable app
  main-is:             Main.hs
  build-depends:       base, miso
  default-language:    Haskell2010

Use cabal2nix to generate a file named app.nix that looks like below.

➜  cabal2nix . --compiler ghcjs > app.nix
➜  cat app.nix
{ mkDerivation, base, miso, stdenv }:
mkDerivation {
  pname = "app";
  version = "";
  src = ./.;
  isLibrary = false;
  isExecutable = true;
  executableHaskellDepends = [ base miso ];
  description = "First miso app";
  license = stdenv.lib.licenses.unfree;

Write a default.nix (which calls app.nix), this fetches a recent version of miso.

{ pkgs ? import <nixpkgs> {} }:
  result = import (pkgs.fetchFromGitHub {
    owner = "dmjio";
    repo = "miso";
    sha256 = "13wfxxplnqajqnykyxdy7477kdfxshpv800b2shr1iib8m01lygn";
    rev = "91b7194c6e0baab3d367073449a8ada7ba8dc346";
  }) {};
in pkgs.haskell.packages.ghcjs.callPackage ./app.nix {
  miso = result.miso-ghcjs;

Build the project


Open the result

open ./result/bin/app.jsexe/index.html

For development with nix, it's important to have cabal present for building. This command will make it available in your PATH.

nix-env -iA cabal-install -f '<nixpkgs>'

To be put into a shell w/ GHCJS and all the dependencies for this project present, use nix-shell.

nix-shell -A env

To open GHCJSi (NODE_PATH should already be set properly)

$ cabal configure --ghcjs
$ cabal repl
Package has never been configured. Configuring with default flags. If this
fails, please run configure manually.
Resolving dependencies...
Configuring app-
Preprocessing executable 'app' for app-
GHCJSi, version 0.2.0-7.10.3: http://www.github.com/ghcjs/ghcjs/  :? for help
[1 of 1] Compiling Main             ( Main.hs, interpreted )
Ok, modules loaded: Main.
browser connected, code runs in browser from now on


The latest stable version of miso will be available on Hackage. To build with cabal, we assume ghcjs is in your PATH and ghcjs-base is present in your ghcjs-pkg list.

cabal sandbox init
cabal install --ghcjs
cabal build
open dist/build/app/app.jsexe/index.html

GHCJSi Caveats

If you run main in GHCJSi, interrupt it and then run it again, you will end up with two copies of your app displayed above each other. As a workaround, you can use clearBody >> main which will completely clear the document body before rendering your application.


For constructing client and server applications, we recommend using one cabal file with two executable sections, where the buildable attribute set is contingent on the compiler. An example of this layout is here. For more info on how to use stack with a client/server setup, see this link. For more information on how to use nix with a client/server setup, see the nix scripts for https://haskell-miso.org.












Canvas 2D



File Reader




Sample application

-- | Haskell language pragma
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards #-}

-- | Haskell module declaration
module Main where

-- | Miso framework import
import Miso
import Miso.String

-- | Type synonym for an application model
type Model = Int

-- | Sum type for application events
data Action
  = AddOne
  | SubtractOne
  | NoOp
  | SayHelloWorld
  deriving (Show, Eq)

-- | Entry point for a miso application
main :: IO ()
main = startApp App {..}
    initialAction = SayHelloWorld -- initial action to be executed on application load
    model  = 0                    -- initial model
    update = updateModel          -- update function
    view   = viewModel            -- view function
    events = defaultEvents        -- default delegated events
    mountPoint = Nothing          -- mount point for miso on DOM, defaults to body
    subs   = []                   -- empty subscription list

-- | Updates model, optionally introduces side effects
updateModel :: Action -> Model -> Effect Action Model
updateModel AddOne m = noEff (m + 1)
updateModel SubtractOne m = noEff (m - 1)
updateModel NoOp m = noEff m
updateModel SayHelloWorld m = m <# do
  putStrLn "Hello World" >> pure NoOp

-- | Constructs a virtual DOM from a model
viewModel :: Model -> View Action
viewModel x = div_ [] [
   button_ [ onClick AddOne ] [ text "+" ]
 , text (ms (show x))
 , button_ [ onClick SubtractOne ] [ text "-" ]

Building examples

The easiest way to build the examples is with the nix package manager

git clone https://github.com/dmjio/miso && cd miso && nix-build

This will build all examples and documentation into a folder named result

➜  miso git:(master) ✗ tree result -d
|-- doc
|   |-- x86_64-osx-ghc-8.0.2
|   |   `-- miso-
|   |       `-- html
|   |           `-- src
|   `-- x86_64-osx-ghcjs-0.2.0-ghc7_10_3
|       `-- miso-
|           `-- html
|               `-- src
|-- examples
|   |-- mario.jsexe
|   |   `-- imgs
|   |       |-- jump
|   |       |-- stand
|   |       `-- walk
|   |-- router.jsexe
|   |-- simple.jsexe
|   |-- tests.jsexe
|   |-- todo-mvc.jsexe
|   `-- websocket.jsexe

To see examples, we recommend hosting them with a webserver

cd result/examples/todo-mvc.jsexe && python -m SimpleHTTPServer
Serving HTTP on port 8000 ...




Feel free to dive in! Open an issue or submit PRs.

See CONTRIBUTING for more info.


BSD3 © David Johnson

comments powered byDisqus