Work in progress integration of PureScript (see https://www.purescript.org) into Yesod.

Goals:

• environment for easy PureScript development (with dev flag):
  • auto refresh: sources compiled on demand or when file changes, with cache,
  • convenient display of error messages.
• a way of embedding compiled PureScript into final app binary using TemplateHaskell.

1. Clone repo: git clone https://github.com/mpietrzak/yesod-purescript.git
2. Add source to cabal sandbox: cd yout_project_dir && cabal sandbox add-source path_to_yesod_purescript_clone.

See https://github.com/mpietrzak/yesod-purescript-sample/.

The easiest way is to look at second commit in sample's repo: https://github.com/mpietrzak/yesod-purescript-sample/commit/6e026b63deac97ac55c710e8fcf1f4e550a07bb3

To use yesod-purescript, you have to:

1. add yesod-purescript dependency to your project's cabal file,
2. add a field in app's data type for PureScriptSite and add instance of YesodPurescript typeclass for your app's data type,
3. add subsite route to PureScriptSite,
4. put your purs files in configured subdirectories of your project; by default those directories are:
   • purs - your code,
   • bower_components - dependencies (since most likely you'll use bower to get those).
5. Reference your code in HTML pages.

See https://github.com/mpietrzak/yesod-purescript-sample/.

Rather verbose step by step instructions follow.

Add yesod-purescript to build-depends in .cabal file.

Assuming you have basic project generated by running yesod init.

Go to Foundation.hs.

First add Yesod.PureScrtipt import to this file.

Notice fields in your App data like:

appLogger :: Logger

Add similar line for PureScript at the end:

appPureScript :: PureScriptSite.

Then add instance of YesodPureScript: instance YesodPureScript App. You can add this after all other instances (order does not really matter).

Go to Application.hs:

• add import of Yesod.PureScript,
• find makeFoundation function,
  • add appPureScript <- createYesodPureScriptSite def close to top of this function.

Add this line to config/routes after auth route definition:

/purs PureScriptR PureScriptSite appPureScript

This attaches Yesod PureScript Subsite at /purs. Opening url http://localhost:3000/purs/Foo.js will try to find and compile module Foo.

There's also status page at http://localhost:3000/purs which lists loaded modules and module loading errors (if any).

Put Hello.purs in purs subdirectory:

module Hello (main)
where

import Control.Monad.Eff

foreign import log
"""function log(s) {
    return function() {
        return window.console.log(s);
    };
}""" :: forall eff. String -> Eff eff {}

main = log "hello"

Create empty bower_components dir in your project dir.

Start dev server and open http://localhost:3000/purs/Hello.js.

Open Handler/Home.hs. Add import: import Yesod.PureScript (getPureScriptRoute). Change getHomeR to reference your Hello.js script using addScript:

getHomeR :: Handler Html
getHomeR = do
    (formWidget, formEnctype) <- generateFormPost sampleForm
    let submission = Nothing :: Maybe (FileInfo, Text)
        handlerName = "getHomeR" :: Text
    defaultLayout $ do
        aDomId <- newIdent
        setTitle "Welcome To Yesod!"
        addScript $ PureScriptR $ getPureScriptRoute ["Hello"]
        $(widgetFile "homepage")