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PureScript loader for webpack

  • Supports hot-reloading and rebuilding of single source files
  • Dead code elimination using the bundle option
  • Colorized build output using purescript-psa and the psc: "psa" option


Install with npm.

// For PureScript 0.9 and newer
npm install purs-loader --save-dev
// For PureScript 0.8
npm install purs-loader@purescript-0.8 --save-dev


const webpackConfig = {
  // ... 
  loaders: [
    // ... 
      test: /\.purs$/,
      loader: 'purs-loader',
      exclude: /node_modules/,
      query: {
        psc: 'psa',
        src: ['bower_components/purescript-*/src/**/*.purs', 'src/**/*.purs']
    // ... 
  // ... 

Refer to the purescript-webpack-example for a more detailed example.


Default options:

const loaderConfig = {
  psc: 'psc',
  pscArgs: {},
  pscBundle: 'psc-bundle',
  pscBundleArgs: {},
  pscIde: false, // instant rebuilds using psc-ide-server (experimental) 
  pscIdeArgs: {}, // for example, to use different psc-ide-server port: {port: 4088} 
  pscIdeServerArgs: {}, // for example, to change the port { port: 4088 } 
  pscIdeColors: false, // defaults to true if psc === 'psa' 
  pscPackage: false,
  bundleOutput: 'output/bundle.js',
  bundleNamespace: 'PS',
  bundle: false,
  warnings: true,
  watch: false, // indicates if webpack is in watch mode 
  output: 'output',
  src: [
    path.join('src', '**', '*.purs'),
    // if pscPackage = false 
    path.join('bower_components', 'purescript-*', 'src', '**', '*.purs')
    // if pscPackage = true 
    // source paths reported by `psc-package sources` 

psc-ide support (experimental)

Experimental support for instant rebuilds using psc-ide-server can be enabled via the pscIde: true option. You can use an already running psc-ide-server instance by specifying the port in pscIdeArgs, if there is no server running this loader will start one for you.

psc-package support (experimental)

Set pscPackage query parameter to true to enable psc-package support. The psc-package-supplied source paths will be appended to src parameter.


Slower webpack startup after enabling psc-ide support?

By default, the psc-ide-server will be passed the globs from query.src, this is helpful for other tools using psc-ide-server (for example IDE plugins), however it might result in a slower initial webpack startup time (rebuilds are not affected). To override the default behaviour, add: pscIdeServerArgs: { "_": ['your/*globs/here'] } to the loader config

Errors not being displayed in watch mode?

When the watch option is set to true, psc errors are appended to webpack's compilation instance errors array and not passed back as an error to the loader's callback. This may result in the error not being reported by webpack. To display errors, the following plugin may be added to the webpack config.

const webpackConfig = {
  // ... 
  plugins: [
      this.plugin('done', function(stats){
  // ... 

Error spawn ENOENT

This is caused when the loader tries to spawn a binary that does not exists (file or directory not found). If you call webpack like webpack or webpack --watch, then ensure that all required binaries that the loader depends on are available in your $PATH.

If you run webpack through an npm script (e.g., npm run or npm start) on NixOS, then it will first attempt to find binaries in node_packages/.bin. If you have the compiler installed through npm and it finds it there, this will cause ENOENTon Nix, because the binary needs to be patched first, but npm will install the binary that is linked with /lib64/ - a file that will not exist at that path in NixOS. The solution is to simply use the compiler from haskellPackages.purescript and make sure that it's available in $PATH. For more information about how to make it work on Nix, see Purescript Webpack Example