Add MonadFail instance

In order to build on GHC 8.8.3 (via Stackage snapshot lts-15.8) there
needed to be a MonadFail instance for the Parser monad.

Author: istathar

src/Vimus/Command/Parser.hs

@@ -40,10 +40,12 @@ instance Applicative Parser where
   (<*>) = ap
 
 instance Monad Parser where
-  fail      = parserFail . ParseError
   return a  = Parser $ \input -> Right (a, input)
   p1 >>= p2 = Parser $ \input -> runParser p1 input >>= uncurry (runParser . p2)
 
+instance MonadFail Parser where
+  fail      = parserFail . ParseError
+
 instance Alternative Parser where
   empty = parserFail Empty
   p1 <|> p2 = Parser $ \input -> case runParser p1 input of

stack.yaml

@@ -1 +1 @@
-resolver: lts-13.12
+resolver: lts-15.8