Dynamic / Dispatch

dispatch.hs

module Dispatch where

import Data.Dynamic
import Control.Monad.Reader.Class

-- THINGS WE WANT
-- 1. we want to avoid having to duplicate the type of the members of a 
--    type class in our test (like Fixture)
-- 2. we want to be able to record the arguments applied to a test function
-- 3. we want to be able to control the return value from a test function
-- 4. we want to be able to control #2 and #3 from inside the "it-block"

type Testy = ReaderT Dispatch IO

type Dispatch = (Typeable a) => String -> a

instance Timeful Testy where
  currentPOSIXTime = asks ($ "currentPOSIXTime")

instance Persistence Testy where
  insertDeveloper = asks ($ "insertDeveloper")
  
override :: MonadReader Dispatch m => String -> Dynamic -> m a -> m a
override name f act = local alter act
  where
    alter dict method = if method == name then fromDyn (error "woops wrong type") f else dict method


t :: Testy a -> Testy a
t = id

f :: Something -> Testy a

let f _ = t $ error "omgbbq"
override "insertDeveloper" f