94 lines
2.6 KiB
Markdown
94 lines
2.6 KiB
Markdown
# servant-js
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This library lets you derive automatically (JQuery based) Javascript functions that let you query each endpoint of a *servant* webservice.
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## Example
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Read more about the following example [here](https://github.com/haskell-servant/servant/tree/master/servant-jquery/tree/master/examples#examples).
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``` haskell
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{-# LANGUAGE DataKinds #-}
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{-# LANGUAGE TypeOperators #-}
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{-# LANGUAGE DeriveGeneric #-}
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{-# LANGUAGE GeneralizedNewtypeDeriving #-}
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import Control.Concurrent.STM
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import Control.Monad.IO.Class
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import Data.Aeson
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import Data.Proxy
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import GHC.Generics
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import Network.Wai.Handler.Warp (run)
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import Servant
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import Servant.JQuery
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import System.FilePath
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-- * A simple Counter data type
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newtype Counter = Counter { value :: Int }
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deriving (Generic, Show, Num)
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instance ToJSON Counter
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-- * Shared counter operations
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-- Creating a counter that starts from 0
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newCounter :: IO (TVar Counter)
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newCounter = newTVarIO 0
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-- Increasing the counter by 1
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counterPlusOne :: MonadIO m => TVar Counter -> m Counter
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counterPlusOne counter = liftIO . atomically $ do
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oldValue <- readTVar counter
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let newValue = oldValue + 1
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writeTVar counter newValue
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return newValue
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currentValue :: MonadIO m => TVar Counter -> m Counter
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currentValue counter = liftIO $ readTVarIO counter
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-- * Our API type
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type TestApi = "counter" :> Post Counter -- endpoint for increasing the counter
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:<|> "counter" :> Get Counter -- endpoint to get the current value
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:<|> Raw -- used for serving static files
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testApi :: Proxy TestApi
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testApi = Proxy
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-- * Server-side handler
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-- where our static files reside
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www :: FilePath
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www = "examples/www"
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-- defining handlers
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server :: TVar Counter -> Server TestApi
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server counter = counterPlusOne counter -- (+1) on the TVar
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:<|> currentValue counter -- read the TVar
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:<|> serveDirectory www -- serve static files
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runServer :: TVar Counter -- ^ shared variable for the counter
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-> Int -- ^ port the server should listen on
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-> IO ()
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runServer var port = run port (serve testApi $ server var)
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-- * Generating the JQuery code
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incCounterJS :<|> currentValueJS :<|> _ = jquery testApi
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writeJS :: FilePath -> [AjaxReq] -> IO ()
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writeJS fp functions = writeFile fp $
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concatMap generateJS functions
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main :: IO ()
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main = do
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-- write the JS code to www/api.js at startup
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writeJS (www </> "api.js")
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[ incCounterJS, currentValueJS ]
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-- setup a shared counter
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cnt <- newCounter
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-- listen to requests on port 8080
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runServer cnt 8080
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```
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