Rackla Types (in my mind, at least)

Rackla.hs

module Main where

import Control.Applicative

-- value with type a is only for demo purposes, it would be supplied
-- asyncronously in Rackla (or with messages, I don't know how it works
-- exactly).
data PID a = PID a deriving (Show)

instance Functor PID where
  fmap f (PID p) = PID (f p)

data Rackla a = Rackla [PID a] deriving (Show)

instance Functor Rackla where
  fmap f (Rackla pids) = Rackla (map (fmap f) pids)

----------------------------------------
-- Here begins the Rackla.HTTP module,
-- which is the fun stuff.
----------------------------------------

type Response = String

-- Create some responses, which are just the request URLs in this demo.
request :: [String] -> Rackla Response
request urls = Rackla $ map (\x -> PID $ "Request for " ++ x) urls

-- Dummy implementation of some transforming function.
setSomeHeader :: Response -> Response
setSomeHeader = id

main :: IO ()
main = print (setSomeHeader <$> request ["some", "crazy", "urls"]) -- <$> is infix "fmap"

This has no asynchronicity at all for the purpose of being terse.