RWSMonads.hs

module RWSMonads where

import Control.Monad.Reader (Reader, runReader, ask)
import Control.Monad.State  (State, runState, evalState, get, put) -- also gets/modify
import Control.Monad.Writer (Writer, runWriter, tell)

getSetCount :: Reader String Int
getSetCount = do
  endpoint <- ask
  return $ length endpoint

doStuffWithLogging :: String -> Writer String ()
doStuffWithLogging endpoint = do
  tell $ "hello " ++ endpoint ++ "\n"
  tell "asdhasdfhgasfg\n"
  return ()

-- String -- just an argument to a fn (no part of State stuff)
-- Int    -- state that you can access with get/put
-- Bool   -- what function returns
doStuffWithState :: String -> State Int Bool
doStuffWithState arg = do
  s <- get
  put (s + length arg)
  return True

main :: IO ()
main = do
  let r      = runReader getSetCount "http://api.factual.com/sets"
  let (r, w) = runWriter (doStuffWithLogging "http://api.factual.com/sets")

  let (r, s) = runState  (doStuffWithState "someArg") 12345 -- return result and state
  let  r     = evalState (doStuffWithState "someArg") 12345 -- return result only
  
  return ()