Real Haskell Program Samples

CommandLine.hs

#!/usr/bin/env stack
-- stack --resolver lts-12.12 script

import Options.Applicative.Simple
import Data.Semigroup ((<>))

data Sample =
  Sample
    { sampleEnable :: Bool
    , sampleUrl :: String
    } deriving (Show)

main = do
  (opts, ()) <-
    simpleOptions
      "1.0"
      "Demo opts program"
      "This program demonstrates commandline options."
      (Sample
        <$> flag False True (long "enable-the-thing" <> short 'e' <> help "Enable it!")
        <*> strArgument (metavar "URLHERE" <> help "The URL"))
      empty
  print opts

Json.hs

#!/usr/bin/env stack
-- stack --resolver lts-12.12 script

{-# LANGUAGE OverloadedStrings #-}

import Data.Aeson

main = do
  print (decode "{\"age\":50,\"name\":\"Sofia\"}" :: Maybe Value)
  print (encode out)

out :: [(Int, String)]
out = [(1,"Hello"),(2,"World!")]

WebClient.hs

#!/usr/bin/env stack
-- stack --resolver lts-12.12 script

{-# LANGUAGE OverloadedStrings #-}

import Network.HTTP.Simple
import qualified Data.ByteString.Char8 as B8

main :: IO ()
main = do
  response <- httpBS "http://example.com"
  B8.putStrLn (getResponseBody response)

WebServer.hs

#!/usr/bin/env stack
-- stack --resolver lts-12.12 script

{-# LANGUAGE OverloadedStrings #-}

import Network.Wai
import Network.HTTP.Types
import Network.Wai.Handler.Warp (run)

app :: Application
app _ respond = do
    putStrLn "I've done some IO here"
    respond 
      (responseLBS
        status200
        [("Content-Type", "text/plain")]
        "Hello, Web!")

main :: IO ()
main = do
    putStrLn "http://localhost:8080/"
    run 8080 app