Implement -XStaticValues

Summary:
As proposed in [1], this extension introduces a new syntactic form
`static e`, where `e :: a` can be any closed expression. The static form
produces a value of type `StaticPtr a`, which works as a reference that
programs can "dereference" to get the value of `e` back. References are
like `Ptr`s, except that they are stable across invocations of a
program.

The relevant wiki pages are [2, 3], which describe the motivation/ideas
and implementation plan respectively.

[1] Jeff Epstein, Andrew P. Black, and Simon Peyton-Jones. Towards
Haskell in the cloud. SIGPLAN Not., 46(12):118–129, September 2011. ISSN
0362-1340.
[2] https://ghc.haskell.org/trac/ghc/wiki/StaticPointers
[3] https://ghc.haskell.org/trac/ghc/wiki/StaticPointers/ImplementationPlan

Authored-by: Facundo Domínguez <facundo.dominguez@tweag.io>
Authored-by: Mathieu Boespflug <m@tweag.io>
Authored-by: Alexander Vershilov <alexander.vershilov@tweag.io>

Test Plan: `./validate`

Reviewers: hvr, simonmar, simonpj, austin

Reviewed By: simonpj, austin

Subscribers: qnikst, bgamari, mboes, carter, thomie, goldfire

Differential Revision: https://phabricator.haskell.org/D550

GHC Trac Issues: #7015

7 files changed, 64 insertions, 0 deletions

diff --git a/testsuite/tests/typecheck/should_fail/TcStaticPointersFail01.hs b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail01.hs
new file mode 100644
index 0000000000..7221b7369b
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail01.hs
@@ -0,0 +1,11 @@
+{-# LANGUAGE StaticPointers   #-}
+
+module StaticPointersFail01 where
+
+import GHC.StaticPtr
+
+f0 :: StaticPtr Int
+f0 = static g
+
+g :: Int -> Int
+g = id
diff --git a/testsuite/tests/typecheck/should_fail/TcStaticPointersFail01.stderr b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail01.stderr
new file mode 100644
index 0000000000..e41ec7443d
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail01.stderr
@@ -0,0 +1,6 @@
+
+TcStaticPointersFail01.hs:8:13:
+    Couldn't match expected type ‘Int’ with actual type ‘Int -> Int’
+    Probable cause: ‘g’ is applied to too few arguments
+    In the body of a static form: g
+    In the expression: static g
diff --git a/testsuite/tests/typecheck/should_fail/TcStaticPointersFail02.hs b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail02.hs
new file mode 100644
index 0000000000..3b4d0ff661
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail02.hs
@@ -0,0 +1,12 @@
+{-# LANGUAGE StaticPointers     #-}
+{-# LANGUAGE ImpredicativeTypes #-}
+
+module StaticPointersFail02 where
+
+import GHC.StaticPtr
+
+f1 :: StaticPtr ((forall a . a -> a) -> b)
+f1 = static (undefined :: (forall a . a -> a) -> b)
+
+f2 :: StaticPtr (Monad m => a -> m a)
+f2 = static return
diff --git a/testsuite/tests/typecheck/should_fail/TcStaticPointersFail02.stderr b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail02.stderr
new file mode 100644
index 0000000000..f11ec28f18
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail02.stderr
@@ -0,0 +1,14 @@
+
+TcStaticPointersFail02.hs:9:6:
+    No instance for (Data.Typeable.Internal.Typeable b)
+      arising from a static form
+    In the expression: static (undefined :: (forall a. a -> a) -> b)
+    In an equation for ‘f1’:
+       f1 = static (undefined :: (forall a. a -> a) -> b)
+
+TcStaticPointersFail02.hs:12:6:
+    No instance for (Data.Typeable.Internal.Typeable Monad)
+      (maybe you haven't applied enough arguments to a function?)
+      arising from a static form
+    In the expression: static return
+    In an equation for ‘f2’: f2 = static return
diff --git a/testsuite/tests/typecheck/should_fail/TcStaticPointersFail03.hs b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail03.hs
new file mode 100644
index 0000000000..58e06ee1d8
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail03.hs
@@ -0,0 +1,9 @@
+{-# LANGUAGE StaticPointers     #-}
+
+module StaticPointersFail03 where
+
+import GHC.StaticPtr
+import Data.Typeable
+
+f1 :: (Typeable a, Typeable m, Monad m) => a -> m a
+f1 = deRefStaticPtr (static return)
diff --git a/testsuite/tests/typecheck/should_fail/TcStaticPointersFail03.stderr b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail03.stderr
new file mode 100644
index 0000000000..03a01df842
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/TcStaticPointersFail03.stderr
@@ -0,0 +1,6 @@
+
+TcStaticPointersFail03.hs:9:29:
+    No instance for (Monad m) arising from a use of ‘return’
+    In the body of a static form: return
+    In the first argument of ‘deRefStaticPtr’, namely ‘(static return)’
+    In the expression: deRefStaticPtr (static return)
diff --git a/testsuite/tests/typecheck/should_fail/all.T b/testsuite/tests/typecheck/should_fail/all.T
index d3c8941c65..1546b3ae8c 100644
--- a/testsuite/tests/typecheck/should_fail/all.T
+++ b/testsuite/tests/typecheck/should_fail/all.T
@@ -328,6 +328,12 @@ test('ContextStack2', normal, compile_fail, ['-ftype-function-depth=10'])
 test('T8570', extra_clean(['T85570a.o', 'T8570a.hi','T85570b.o', 'T8570b.hi']),
      multimod_compile_fail, ['T8570', '-v0'])
 test('T8603', normal, compile_fail, [''])
+test('TcStaticPointersFail01',
+     when(compiler_lt('ghc', '7.9'), skip), compile_fail, [''])
+test('TcStaticPointersFail02',
+     when(compiler_lt('ghc', '7.9'), skip), compile_fail, [''])
+test('TcStaticPointersFail03',
+     when(compiler_lt('ghc', '7.9'), skip), compile_fail, [''])
 test('T8806', normal, compile_fail, [''])
 test('T8912', normal, compile_fail, [''])
 test('T9033', normal, compile_fail, [''])