Support GHC 8.8

As part of the MonadFail proposal[1], the fail method was removed from
the Monad type class in GHC 8.8.  As such, one now needs a MonadFail
constraint for the relevant functions.

[1]: https://wiki.haskell.org/MonadFail_Proposal

1 files changed, 1 insertions, 1 deletions

diff --git a/Val.hs b/Val.hs
index f024b9d..5c52c82 100644
--- a/Val.hs
+++ b/Val.hs
@@ -42,7 +42,7 @@ instance FromJSON Val where
 b64 :: B.ByteString -> T.Text
 b64 = T.decodeUtf8 . B64.encode
 
-unb64 :: Monad m => T.Text -> m B.ByteString
+unb64 :: MonadFail m => T.Text -> m B.ByteString
 unb64 t = either
 	(\_ -> fail "bad base64 data")
 	return