diff options
Diffstat (limited to 'testsuite/tests/typecheck/should_run/tcrun030.hs')
-rw-r--r-- | testsuite/tests/typecheck/should_run/tcrun030.hs | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/testsuite/tests/typecheck/should_run/tcrun030.hs b/testsuite/tests/typecheck/should_run/tcrun030.hs new file mode 100644 index 0000000000..fe28a33091 --- /dev/null +++ b/testsuite/tests/typecheck/should_run/tcrun030.hs @@ -0,0 +1,20 @@ +{-# LANGUAGE UndecidableInstances #-} + +-- Test recursive dictionaries + +module Main where + +data D r = ZeroD | SuccD (r (D r)); + +instance (Eq (r (D r))) => Eq (D r) where + ZeroD == ZeroD = True + (SuccD a) == (SuccD b) = a == b + _ == _ = False; + +equalDC :: D [] -> D [] -> Bool; +equalDC = (==); + +foo :: D [] +foo = SuccD [SuccD [ZeroD], ZeroD] + +main = print (foo == foo) |