Pfthb

i get the basic functionality of the reader-monad from learnyouahaskell book and i've seen some advises here to make use of it for dependency-injection.
even there are some examples here on stackoverflow, i dont know how to use it for integration-testing.

my code is:

list :: Ctx -> [String] -> IO String
list ctx args = do
 d <- eitherDecode <$> Uplink.get (token ctx) (endpointActivities ctx) :: IO (Either String Activities)
 case d of 
 Left err -> return err 
 Right result -> return $ unlines . filterByPrefix (parsePrefix args) . extractNames $ activities result

uplink.hs

get :: String -> String -> IO B.ByteString
get token endpoint = do
 req <- parseRequest endpoint
 resp <- httpLBS $ withAuth token req
 return $ getResponseBody resp

how can i mock the httpLBS - call for integration-testing with the reader-monad?

EDIT: !!!!

i almost have it now with the reader-monad. the only problem left is that i dont know how i can define that httpsLBS-function in my Ctx-data-type.

httpLBS-function-signature:

httpLBS :: MonadIO m => Request -> m (Response ByteString) 

my Ctx data-type-definition:

data Ctx =
 Ctx 
 token :: String,
 endpointActivities :: String,
 endpointTimeTrackingStart :: String,
 httpLBSFunc :: MonadIO m => Request -> m (Response ByteString)
 deriving (Show)

i always get the error: Not in scope: type variable ‘m’
how can i define that function in my Ctx-data-type with its constraints?

i promise, that i will post my solution afterwards, when this last problem is solved

In Haskell, dependency injection is just higher order programming + currying. You can write your code as the following.

-- where (? -> ?) is the type of httpLBS
get_ :: (? -> ?) -> String -> String -> IO B.ByteString
get_ httpFunc token endpoint = do
 req <- parseRequest endpoint
 resp <- httpFunc $ withAuth token req
 return $ getResponseBody resp

getProduction = get_ httpLBS

getTest = get_ httpMock