[commit: testsuite] master: Test irreducible-evidence self-interactive (723804d)

[Max Bolingbroke]

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

On branch  : master

http://hackage.haskell.org/trac/ghc/changeset/723804de2a49e5013807fb8c2a04569d086ebfd0

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

commit 723804de2a49e5013807fb8c2a04569d086ebfd0
Author: Max Bolingbroke <batterseapower at hotmail.com>
Date:   Sat Sep 10 14:31:58 2011 +0100

    Test irreducible-evidence self-interactive

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

 tests/typecheck/should_compile/all.T    |    1 +
 tests/typecheck/should_compile/tc257.hs |   23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/tests/typecheck/should_compile/all.T b/tests/typecheck/should_compile/all.T
index 0cc90f0..e185708 100644
--- a/tests/typecheck/should_compile/all.T
+++ b/tests/typecheck/should_compile/all.T
@@ -348,6 +348,7 @@ test('tc253', normal, compile, [''])
 test('tc254', normal, compile, [''])
 test('tc255', normal, compile, [''])
 test('tc256', normal, compile, [''])
+test('tc257', normal, compile, [''])
 
 test('GivenOverlapping', normal, compile, [''])
 test('SilentParametersOverlapping', normal, compile, [''])
diff --git a/tests/typecheck/should_compile/tc257.hs b/tests/typecheck/should_compile/tc257.hs
new file mode 100644
index 0000000..b1db39f
--- /dev/null
+++ b/tests/typecheck/should_compile/tc257.hs
@@ -0,0 +1,23 @@
+{-# LANGUAGE KindSignatures, ConstraintKinds, MultiParamTypeClasses, FlexibleInstances, UndecidableInstances #-}
+module Ctx where
+
+data Proxy (ctxt :: * -> Constraint) = Proxy
+
+-- At one time, this one worked:
+nonmeth :: ctxt Int => Proxy ctxt -> a
+nonmeth prox = nonmeth prox
+
+
+class Foo (ctxt :: * -> Constraint) a where
+    meth :: ctxt a => Proxy ctxt -> a
+
+instance ctxt Int => Foo ctxt Int where
+    -- But this one didn't:
+    meth prox = meth prox
+
+-- The error was:
+-- Could not deduce (ctxt Int) arising from a use of `meth'
+-- from the context (ctxt Int)
+
+-- The problem was that irreducible evidence did not interact with
+-- evidence of equal type.
\ No newline at end of file