Try to compile with GHC 8.0.1

.travis.yml

@@ -22,8 +22,6 @@ matrix:
     - env: CABALVER=1.24 GHCVER=8.0.1
       compiler: ": #GHC 8.0.1"
       addons: {apt: {packages: [cabal-install-1.24,ghc-8.0.1], sources: [hvr-ghc]}}
-  allow_failures:
-    - env: CABALVER=1.24 GHCVER=8.0.1
 
 before_install:
  - unset CC

Haxl/Core/Monad.hs

@@ -740,6 +740,7 @@ cachedComputation req haxl = GenHaxl $ \env ref -> do
   -- continuation: just try to evaluate the memo again.  We know it is
   -- already in the cache (because we just checked), so the computation
   -- will never be used.
+  retryMemo :: (Typeable (req a)) => req a -> GenHaxl u a
   retryMemo req =
    cachedComputation req (throw (CriticalError "retryMemo"))