added error handling to the web request (and changed from req to wreq)

app/Requester.hs

@@ -1,18 +1,25 @@
 {-# LANGUAGE OverloadedStrings, DataKinds#-}
 module Requester(request) where
   
-import Network.HTTP.Req
--- import qualified Data.Text as T
-import Control.Monad.IO.Class(MonadIO)
-import qualified Data.ByteString as B
+import qualified Network.Wreq as N
+import Network.HTTP.Client (HttpException)
+import qualified Control.Exception as E
+import Control.Lens.Getter ((^.))
+import qualified Data.ByteString.Lazy as LBS
+import Monad
 
-url :: Url 'Https
-url = https "md.darmstadt.ccc.de" /: "mathechor-probenplanung" /: "download"
+url :: String
+url = "https://md.darmstadt.ccc.de/mathechor-probenplanung/download"
 
+eitherToFail :: (Show a, MonadFail m) => Either a b -> m b
+eitherToFail (Right a) = return a
+eitherToFail (Left b)  = fail $ show b
 
-
-requestRunner :: (MonadIO m)=> m BsResponse
-requestRunner = runReq defaultHttpConfig $ req GET url NoReqBody bsResponse mempty
-
-request :: (MonadIO m) => m B.ByteString
-request = fmap responseBody requestRunner
+request :: (MonadIO m, MonadFail m) => m LBS.ByteString
+request = do
+  -- catch might seem to be more convenient instead of catch. But the handler in catch forces
+  -- IO and not MonadIO, so we can't call fail. We use try to escape so we can escape IO first
+  -- and then handle the error (with fail in scope)
+  responseWithError <- liftIO (E.try (N.get url) :: IO (Either HttpException (N.Response LBS.ByteString)))
+  response <- eitherToFail responseWithError
+  return $ response ^. N.responseBody  

app/TableParser.hs

@@ -3,12 +3,11 @@ module TableParser(MailRecord(..), parseBString, parseTable) where
   
 import qualified Text.Parsec as P
 -- import qualified Text.Parsec.Char as P
-import qualified Text.Parsec.Text as P
+import qualified Text.Parsec.Text.Lazy as P
 import qualified Data.Text.Lazy as LT
-import qualified Data.Text as ST
-import qualified Data.Text.Encoding as ST
+import qualified Data.Text.Lazy.Encoding as LT
 import qualified Data.Time.Calendar as D
-import qualified Data.ByteString as B
+import qualified Data.ByteString.Lazy as B
 import Control.Monad(void)
 
 
@@ -70,7 +69,7 @@ parseTable = do
   P.eof
   return x
 
-textToMailRecord :: ST.Text -> Either String [MailRecord]
+textToMailRecord :: LT.Text -> Either String [MailRecord]
 textToMailRecord t = case P.parse parseTable "" t of
   Left x -> Left $ show x
   Right x -> Right x
@@ -81,7 +80,7 @@ parseBString t = do
   text <- toText t
   textToMailRecord text
 
-toText :: B.ByteString -> Either String ST.Text
-toText t = case ST.decodeUtf8' t of
+toText :: B.ByteString -> Either String LT.Text
+toText t = case LT.decodeUtf8' t of
   Left x -> Left $ show x
   Right x -> Right x