diff --git a/brat/Brat/Checker/Monad.hs b/brat/Brat/Checker/Monad.hs
index 12f15aca..1a5cd1d4 100644
--- a/brat/Brat/Checker/Monad.hs
+++ b/brat/Brat/Checker/Monad.hs
@@ -83,7 +83,8 @@ mkFork :: String -> Free sig () -> Free sig ()
 mkFork d par = thTrace ("Forking " ++ d) $ Fork d par $ pure ()
 
 mkYield :: String -> S.Set End -> Free sig ()
-mkYield desc es = thTrace ("Yielding in " ++ desc ++ "\n  " ++ show es) $ Yield (AwaitingAny es) (\_ -> trackM ("woke up " ++ desc) >> Ret ())
+mkYield desc es = thTrace ("Yielding in " ++ desc ++ "\n  " ++ show es) $
+  Yield (AwaitingAny es) (\_ -> trackM ("woke up " ++ desc) >> Ret ())
 
 -- Commands for synchronous operations
 data CheckingSig ty where
diff --git a/brat/Brat/Error.hs b/brat/Brat/Error.hs
index dbccdbb1..31a174a6 100644
--- a/brat/Brat/Error.hs
+++ b/brat/Brat/Error.hs
@@ -11,9 +11,10 @@ module Brat.Error (ParseError(..)
 
 import Brat.FC
 import Data.Bracket
-import Brat.Syntax.Port (PortName)
+import Brat.Syntax.Port (End, PortName)
 
 import Data.List (intercalate)
+import Data.Set (Set, toList)
 import System.Exit
 
 newtype ParseError = PE { pretty :: String }
@@ -109,6 +110,8 @@ data ErrorMsg
  | ThunkLeftUnders String
  | BracketErr BracketErrMsg
  | RemainingNatHopes [String]
+ | NeedToKnow (Set End)
+ | Both ErrorMsg ErrorMsg
 
 instance Show ErrorMsg where
   show (TypeErr x) = "Type error: " ++ x
@@ -194,6 +197,8 @@ instance Show ErrorMsg where
   show (ThunkLeftUnders unders) = "Expected function to return additional values of type: " ++ unders
   show (BracketErr msg) = show msg
   show (RemainingNatHopes hs) = unlines ("Expected to work out values for these holes:":(("    " ++) <$> hs))
+  show (NeedToKnow ends) = unlines $ "I wanna know what:" : ((' ':) . show <$> toList ends) ++ ["is."]
+  show (Both err1 err2) = unlines [show err1,""," AND ALSO","",show err2]
 
 data Error = Err { fc  :: Maybe FC
                  , msg :: ErrorMsg
diff --git a/brat/Control/Monad/Freer.hs b/brat/Control/Monad/Freer.hs
index ed8b7455..a7ddf59d 100644
--- a/brat/Control/Monad/Freer.hs
+++ b/brat/Control/Monad/Freer.hs
@@ -13,7 +13,7 @@ import qualified Data.Set as S
 --  * e -> Unstuck means e has been solved
 --  * e -> Awaiting es means the problem's been transferred
 --  * e not in news means no change to e
-newtype News = News (M.Map End Stuck)
+newtype News = News (M.Map End Stuck) deriving Show
 
 updateEnd :: News -> End -> Stuck
 updateEnd (News m) e = case M.lookup e m of