[commit: testsuite] master: Test Trac #7332 (7a7b121)

Repository : ssh://darcs.haskell.org//srv/darcs/testsuite

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/7a7b121393f8bd81008535497bc88d27175e829f

>---------------------------------------------------------------

commit 7a7b121393f8bd81008535497bc88d27175e829f
Author: Simon Peyton Jones <[email protected]>
Date:   Mon Oct 15 11:07:48 2012 +0100

    Test Trac #7332

>---------------------------------------------------------------

 tests/indexed-types/should_compile/T7332.hs |   49 +++++++++++++++++++++++++++
 tests/indexed-types/should_compile/all.T    |    1 +
 2 files changed, 50 insertions(+), 0 deletions(-)

diff --git a/tests/indexed-types/should_compile/T7332.hs b/tests/indexed-types/should_compile/T7332.hs
new file mode 100644
index 0000000..0649741
--- /dev/null
+++ b/tests/indexed-types/should_compile/T7332.hs
@@ -0,0 +1,49 @@
+{-# LANGUAGE NoMonomorphismRestriction #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE FlexibleInstances, FlexibleContexts #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE MagicHash #-}
+
+module Oleg where
+
+import GHC.Exts hiding( build )
+import Data.Monoid
+
+newtype DC d = DC d
+    deriving (Show, Monoid)
+
+instance IsString (DC String) where
+    fromString = DC
+
+
+class Monoid acc => Build acc r where
+    type BuildR r :: *		-- Result type
+    build :: (acc -> BuildR r) -> acc -> r
+
+instance Monoid dc => Build dc (DC dx) where
+    type BuildR (DC dx) = DC dx
+    build tr acc = tr acc
+
+instance (Build dc r, a ~ dc) => Build dc (a->r) where
+    type BuildR (a->r) = BuildR r
+    build tr acc s = build tr (acc `mappend` s)
+
+
+-- The type is inferred
+tspan :: (Monoid d, Build (DC d) r, BuildR r ~ DC d) => r
+tspan = build (id :: DC d -> DC d) mempty
+
+foo = tspan "aa"
+
+{-  Need (Monoid d, Build (DC d) (a -> t), BuildR (a -> t) ~ DC d, IsString a)
+
+BuildR (a -> t) = BuildR t
+Build (DC d) (a -> t) ===>  (Build (DC d) t, a ~ DC d)
+
+ -}
+
+foo1 = tspan (tspan "aa")
+
+bar = tspan "aa" :: DC String
diff --git a/tests/indexed-types/should_compile/all.T b/tests/indexed-types/should_compile/all.T
index 067415d..bdb3bff 100644
--- a/tests/indexed-types/should_compile/all.T
+++ b/tests/indexed-types/should_compile/all.T
@@ -200,5 +200,6 @@ test('T7156', normal, compile, [''])
 test('T5591a', normal, compile, [''])
 test('T5591b', normal, compile, [''])
 test('T7280', normal, compile, [''])
+test('T7332', normal, compile, [''])