diff options
Diffstat (limited to 'testsuite/tests/typecheck/should_compile/T3955.hs')
-rw-r--r-- | testsuite/tests/typecheck/should_compile/T3955.hs | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/testsuite/tests/typecheck/should_compile/T3955.hs b/testsuite/tests/typecheck/should_compile/T3955.hs new file mode 100644 index 0000000000..921753b80a --- /dev/null +++ b/testsuite/tests/typecheck/should_compile/T3955.hs @@ -0,0 +1,24 @@ +{-# LANGUAGE GeneralizedNewtypeDeriving #-} +{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-} + +-- Test for Trac #3955 + +module T3955 where + +class (Monad m) => MonadReader r m +newtype Reader r a = Reader { runReader :: r -> a } + +instance Monad (Reader r) where + (>>=) = error "urk" + return = error "urk" + +instance MonadReader r (Reader r) + +newtype T a x = T (Reader a x) + deriving (Monad, MonadReader a) + +{- +[1 of 1] Compiling Main ( bug.hs, interpreted ) +mkUsageInfo: internal name? a{tv amy} +Ok, modules loaded: Main. +-} |