diff options
Diffstat (limited to 'testsuite/tests/ghc-regress/typecheck/should_fail/SCLoop.hs')
-rw-r--r-- | testsuite/tests/ghc-regress/typecheck/should_fail/SCLoop.hs | 55 |
1 files changed, 0 insertions, 55 deletions
diff --git a/testsuite/tests/ghc-regress/typecheck/should_fail/SCLoop.hs b/testsuite/tests/ghc-regress/typecheck/should_fail/SCLoop.hs deleted file mode 100644 index f3f6a20bc4..0000000000 --- a/testsuite/tests/ghc-regress/typecheck/should_fail/SCLoop.hs +++ /dev/null @@ -1,55 +0,0 @@ -{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-}
-
--- This is a superclass loop test
--- It should fail with a type error, but
--- it's all too easy to succeed with a bogus recursive dictionary
-
-module SCLoop where
-
-class SC a where
- f :: a -> ()
-
-class SC a => A a b where
- op :: a -> b -> ()
- op x _ = f x
-
-instance A a b => A a [b]
--- dfun1 :: \d::(A a b) -> DA (sc d)
-
-instance SC a => A a (Maybe b)
--- dfun2 :: \d::SC a -> DA d
-
-foo = op () ([Just True])
-
-{- Here is the explanation:
-~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-[Wanted] d1 : (A () [Maybe Bool])
-~~~> d1 := dfun1 d2
-[Wanted] d2 : (A () (Maybe Bool))
-~~~> d2 := dfun2 d3
-[Wanted] d3 : SC ()
-[Derived] d4 : SC () d4 := sc d1
-~~~>
- d3 := sc d1
- isGoodRecEv will check:
- d3 == sc d1
- == sc (dfun1 d2)
- == sc (dfun1 (dfun2 d3) ==> PASSES! (gravity = 1)
- This is BAD BAD BAD, because we get a loop
-
- If we had inlined the definitions:
- d3 == sc d1
- == sc (DA (sc d2))
- == sc (DA (sc (DA d3))) ==> DOES NOT! (gravity = 0)
-
-We should get "No instance for SC ()"
--}
-
-
-
-
-
-
-
-
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