Haskell code snipets

The source code below was auto-fetched from: https://gitweb.softwarefools.com/?p=miguel/haskell.git;a=blob;f=snip/snip.hs

import Control.Monad.Writer 
import Control.Monad.State

import Data.Tuple.Extra (dupe,first,second)
import System.Environment (getArgs)
import Control.Parallel.Strategies (parMap,rseq,rdeepseq)

main = do
        mainMonTra
        mainParMap

-- monad transformers in action
mainMonTra = print $ 
       runState (
               runWriterT  (
                   get >>= \a -> 
                   tell ["foo"] >> 
                   put (a*a) >> 
                   tell ["bar"] >> 
                   tell [show a]
                   )
               ) 5

-- parallel Map arguments: sparks maps
mainParMap = do 
          (sparks:max:_) <- fmap (map read) getArgs
          let ranges = uncurry zip . second tail . dupe $ [0,(max`div`sparks)..max]
          let sums   = parMap rdeepseq (\(a,b)->sum [a+1..b]) ranges
          print $ show (sum sums::Integer)

Shebang

You can also use haskell in conjunction with a shebang line as illustrated below:

The source code below was auto-fetched from: https://gitweb.softwarefools.com/?p=miguel/haskell.git;a=blob;f=snip/shebang.hs

#!/usr/bin/env stack
-- stack --resolver lts-12.5 script
{-# LANGUAGE OverloadedStrings #-}
import qualified Data.ByteString.Lazy.Char8 as L8
import           Network.HTTP.Simple

-- https://haskell-lang.org/tutorial/stack-script

main :: IO ()
main = do
    response <- httpLBS "http://httpbin.org/get"

    putStrLn $ "The status code was: " ++
               show (getResponseStatusCode response)
    print $ getResponseHeader "Content-Type" response
    L8.putStrLn $ getResponseBody response