Overloaded Quotation Brackets (#246)

This patch implements overloaded quotation brackets which generalise the
desugaring of all quotation forms in terms of a new minimal interface.

The main change is that a quotation, for example, [e| 5 |], will now
have type `Quote m => m Exp` rather than `Q Exp`. The `Quote` typeclass
contains a single method for generating new names which is used when
desugaring binding structures.

The return type of functions from the `Lift` type class, `lift` and `liftTyped` have
been restricted to `forall m . Quote m => m Exp` rather than returning a
result in a Q monad.

More details about the feature can be read in the GHC proposal.

https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0246-overloaded-bracket.rst

10 files changed, 26 insertions, 11 deletions

diff --git a/testsuite/tests/quotes/T6062.hs b/testsuite/tests/quotes/T6062.hs
index 342850e853..efce7b2752 100644
--- a/testsuite/tests/quotes/T6062.hs
+++ b/testsuite/tests/quotes/T6062.hs
@@ -1,2 +1,3 @@
+{-# LANGUAGE NoMonomorphismRestriction #-}
 module T6062 where
 x = [| False True |]
diff --git a/testsuite/tests/quotes/T8455.hs b/testsuite/tests/quotes/T8455.hs
index 69d1271b40..c55c5272f9 100644
--- a/testsuite/tests/quotes/T8455.hs
+++ b/testsuite/tests/quotes/T8455.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE DataKinds #-}
+{-# LANGUAGE NoMonomorphismRestriction #-}
 
 module T8455 where
 
diff --git a/testsuite/tests/quotes/T8759a.hs b/testsuite/tests/quotes/T8759a.hs
index 37b65d6fcc..c56a363e7a 100644
--- a/testsuite/tests/quotes/T8759a.hs
+++ b/testsuite/tests/quotes/T8759a.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE PatternSynonyms #-}
+{-# LANGUAGE NoMonomorphismRestriction #-}
 
 module T8759a where
 
diff --git a/testsuite/tests/quotes/T9824.hs b/testsuite/tests/quotes/T9824.hs
index 9a2d6fdfef..d8e2098c07 100644
--- a/testsuite/tests/quotes/T9824.hs
+++ b/testsuite/tests/quotes/T9824.hs
@@ -1,4 +1,5 @@
 {-# OPTIONS_GHC -fwarn-unused-matches #-}
+{-# LANGUAGE NoMonomorphismRestriction #-}
 
 module T9824 where
 
diff --git a/testsuite/tests/quotes/TH_bracket1.hs b/testsuite/tests/quotes/TH_bracket1.hs
index 7dee21ba01..bc0126a91d 100644
--- a/testsuite/tests/quotes/TH_bracket1.hs
+++ b/testsuite/tests/quotes/TH_bracket1.hs
@@ -1,6 +1,6 @@
 -- Check that declarations in a bracket shadow the top-level
 -- declarations, rather than clashing with them.
-
+{-# LANGUAGE NoMonomorphismRestriction #-}
 module TH_bracket1 where
 
 foo = 1
diff --git a/testsuite/tests/quotes/TH_bracket2.hs b/testsuite/tests/quotes/TH_bracket2.hs
index 2b06b9eecb..e903b673db 100644
--- a/testsuite/tests/quotes/TH_bracket2.hs
+++ b/testsuite/tests/quotes/TH_bracket2.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE NoMonomorphismRestriction #-}
 module TH_bracket2 where
 
 d_show = [d| data A = A
diff --git a/testsuite/tests/quotes/TH_bracket3.hs b/testsuite/tests/quotes/TH_bracket3.hs
index c746d61cd3..281b8cb081 100644
--- a/testsuite/tests/quotes/TH_bracket3.hs
+++ b/testsuite/tests/quotes/TH_bracket3.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE NoMonomorphismRestriction #-}
 
 module TH_bracket3 where
 
diff --git a/testsuite/tests/quotes/TH_localname.stderr b/testsuite/tests/quotes/TH_localname.stderr
index d872a622b3..6d0ccc91ec 100644
--- a/testsuite/tests/quotes/TH_localname.stderr
+++ b/testsuite/tests/quotes/TH_localname.stderr
@@ -1,21 +1,23 @@
 
 TH_localname.hs:3:11: error:
-    • Ambiguous type variable ‘t0’ arising from a use of ‘Language.Haskell.TH.Syntax.lift’
-      prevents the constraint ‘(Language.Haskell.TH.Syntax.Lift
-                                  t0)’ from being solved.
+    • Ambiguous type variable ‘m0’ arising from a quotation bracket
+      prevents the constraint ‘(Language.Haskell.TH.Syntax.Quote
+                                  m0)’ from being solved.
       Relevant bindings include
-        y :: t0 (bound at TH_localname.hs:3:6)
-        x :: t0 -> Language.Haskell.TH.Lib.Internal.ExpQ
+        x :: t0 -> m0 Language.Haskell.TH.Syntax.Exp
           (bound at TH_localname.hs:3:1)
-      Probable fix: use a type annotation to specify what ‘t0’ should be.
-      These potential instances exist:
-        29 instances involving out-of-scope types
+      Probable fix: use a type annotation to specify what ‘m0’ should be.
+      These potential instance exist:
+        one instance involving out-of-scope types
         (use -fprint-potential-instances to see them all)
-    • In the expression: Language.Haskell.TH.Syntax.lift y
-      In the expression:
+    • In the expression:
         [| y |]
         pending(rn) [<y, Language.Haskell.TH.Syntax.lift y>]
       In the expression:
         \ y
           -> [| y |]
              pending(rn) [<y, Language.Haskell.TH.Syntax.lift y>]
+      In an equation for ‘x’:
+          x = \ y
+                -> [| y |]
+                   pending(rn) [<y, Language.Haskell.TH.Syntax.lift y>]
diff --git a/testsuite/tests/quotes/TH_typed_csp.hs b/testsuite/tests/quotes/TH_typed_csp.hs
new file mode 100644
index 0000000000..4660fffd7f
--- /dev/null
+++ b/testsuite/tests/quotes/TH_typed_csp.hs
@@ -0,0 +1,6 @@
+-- Check that CSP works for typed quotations.. there was no test for this
+-- before apart from the deriving tests.
+{-# LANGUAGE NoMonomorphismRestriction #-}
+module TH_typed_csp where
+
+bar = (\x -> [|| x ||]) ()
diff --git a/testsuite/tests/quotes/all.T b/testsuite/tests/quotes/all.T
index feefc41433..a10da1046f 100644
--- a/testsuite/tests/quotes/all.T
+++ b/testsuite/tests/quotes/all.T
@@ -29,3 +29,4 @@ test('TH_repE1', normal, compile, [''])
 test('TH_repE3', normal, compile, [''])
 test('TH_abstractFamily', normal, compile_fail, [''])
 test('TH_localname', normal, compile_fail, [''])
+test('TH_typed_csp', normal, compile, [''])