Merge branch 'ea/fix-monad-fail' into 'master'

vmmonad: added Monad.Fail compliance for Monad Mnd solving #5

See merge request !2

src/VMMonad.hs

@@ -24,6 +24,7 @@ import Memory (Memory)
 import Annotation (Ann)
 import Opt (OptVal)
 import Control.Monad (ap, liftM)
+import qualified Control.Monad.Fail as Fail
 import qualified Cpu (initialize, rfetch, rstore, rpush, rpop)
 import qualified Code (initialize, cload, cfind, cstore, cfetch)
 import qualified Level (initialize, lfetch, lstore)
@@ -61,6 +62,11 @@ instance Monad Mnd where
             do x <- c r
                case f x of (Mnd c') -> c' r
 
+    fail = Fail.fail
+
+instance Fail.MonadFail Mnd where
+    fail = error "fail: invalid pattern matching"
+
 run :: Mnd a -> IO a
 run (Mnd c) =
     do m <- Memory.initialize 65536 16384