A simple servant sample of Capture

simple_servant_samplel_capture.hs

{-# LANGUAGE DataKinds                  #-}
{-# LANGUAGE DeriveGeneric              #-}
{-# LANGUAGE FlexibleInstances          #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses      #-}
{-# LANGUAGE OverloadedStrings          #-}
{-# LANGUAGE ScopedTypeVariables        #-}
{-# LANGUAGE TypeOperators              #-}

import Control.Monad.IO.Class             -- liftIO
import Control.Monad.Trans.Except         -- Handler
import Data.Aeson.Types                   -- JSON
import Data.Aeson.Parser                  -- JSON
import GHC.Generics
import Network.Wai.Handler.Warp
import Servant

data RetSum = RetSum { fst :: Int, snd :: Int, ret :: Int} deriving (Eq, Show, Generic)

instance ToJSON RetSum

type MyAPI =  "add" :> Capture "fst" Int :> Capture "snd" Int :> Get '[JSON] RetSum

-- add' :: Int -> Int -> ExceptT ServantErr IO RetSum  -- Handler == ExceptT ServantError IO
add' :: Int -> Int -> Handler RetSum
add' f s =  do
         liftIO $ (putStrLn $ logAdd f s )
         return $ RetSum f s (f+s)

logAdd :: Int -> Int -> String
logAdd f s = (show f) ++ "+" ++ (show s) ++ "=" ++ (show (f + s))

myServer :: Server MyAPI
myServer = add'

myProxy :: Proxy MyAPI
myProxy = Proxy

myApp :: Application
myApp = serve myProxy myServer

main :: IO ()
main = run 8081 myApp