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authorDavid Terei <davidterei@gmail.com>2011-07-20 11:09:03 -0700
committerDavid Terei <davidterei@gmail.com>2011-07-20 11:26:35 -0700
commit16514f272fb42af6e9c7674a9bd6c9dce369231f (patch)
treee4f332b45fe65e2a7a2451be5674f887b42bf199 /testsuite/tests/indexed-types/should_fail/T4272.hs
parentebd422aed41048476aa61dd4c520d43becd78682 (diff)
downloadhaskell-16514f272fb42af6e9c7674a9bd6c9dce369231f.tar.gz
Move tests from tests/ghc-regress/* to just tests/*
Diffstat (limited to 'testsuite/tests/indexed-types/should_fail/T4272.hs')
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1 files changed, 22 insertions, 0 deletions
diff --git a/testsuite/tests/indexed-types/should_fail/T4272.hs b/testsuite/tests/indexed-types/should_fail/T4272.hs
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+ {-# LANGUAGE TypeFamilies, ScopedTypeVariables, FlexibleContexts #-}
+module T4272 where
+
+class Family f where
+ terms :: f a -> a
+
+class Family (TermFamily a) => TermLike a where
+ type TermFamily a :: * -> *
+
+laws :: forall a b. TermLike a => TermFamily a a -> b
+laws t = prune t (terms (undefined :: TermFamily a a))
+
+prune :: TermLike a => TermFamily a a -> TermFamily a a -> b
+prune = undefined
+
+-- terms :: Family f => f a -> a
+-- Instantiate with f = TermFamily a
+-- terms :: Family (TermFamily a) => TermFamily a a -> a
+-- (terms (undefined::TermFamily a a) :: Family (TermFamily a) => a
+-- So the call to prune forces the equality
+-- TermFamily a a ~ a
+-- which triggers an occurs check \ No newline at end of file