Refactor the typechecker to use ExpTypes.

The idea here is described in [wiki:Typechecker]. Briefly,
this refactor keeps solid track of "synthesis" mode vs
"checking" in GHC's bidirectional type-checking algorithm.
When in synthesis mode, the expected type is just an IORef
to write to.

In addition, this patch does a significant reworking of
RebindableSyntax, allowing much more freedom in the types
of the rebindable operators. For example, we can now have
`negate :: Int -> Bool` and
`(>>=) :: m a -> (forall x. a x -> m b) -> m b`. The magic
is in tcSyntaxOp.

This addresses tickets #11397, #11452, and #11458.

Tests:
  typecheck/should_compile/{RebindHR,RebindNegate,T11397,T11458}
  th/T11452

4 files changed, 19 insertions, 13 deletions

diff --git a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail03.hs b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail03.hs
index d1981846df..25d859d2a8 100644
--- a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail03.hs
+++ b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail03.hs
@@ -1,3 +1,3 @@
 {-# LANGUAGE OverloadedLists #-}
 
-main = print (length ['a',"b"])
+main = print (length (['a',"b"] :: [Char]))
diff --git a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail03.stderr b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail03.stderr
index 9c2e41640e..4d55087e18 100644
--- a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail03.stderr
+++ b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail03.stderr
@@ -1,6 +1,9 @@
 
-overloadedlistsfail03.hs:3:27:
-    Couldn't match expected type ‘Char’ with actual type ‘[Char]’
-    In the expression: "b"
-    In the first argument of ‘length’, namely ‘['a', "b"]’
-    In the first argument of ‘print’, namely ‘(length ['a', "b"])’
+overloadedlistsfail03.hs:3:28: error:
+    • Couldn't match type ‘[Char]’ with ‘Char’
+      Expected type: GHC.Exts.Item [Char]
+        Actual type: [Char]
+    • In the expression: "b"
+      In the first argument of ‘length’, namely ‘(['a', "b"] :: [Char])’
+      In the first argument of ‘print’, namely
+        ‘(length (['a', "b"] :: [Char]))’
diff --git a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail05.hs b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail05.hs
index 3601c6e2f1..7059b4b5aa 100644
--- a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail05.hs
+++ b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail05.hs
@@ -1,3 +1,3 @@
 {-# LANGUAGE OverloadedLists #-}
 
-main = print (length ['a'..(10 :: Int)])
+main = print (length (['a'..(10 :: Int)] :: [Int]))
diff --git a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail05.stderr b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail05.stderr
index c576b5868c..edd0c7fcef 100644
--- a/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail05.stderr
+++ b/testsuite/tests/overloadedlists/should_fail/overloadedlistsfail05.stderr
@@ -1,7 +1,10 @@
 
-overloadedlistsfail05.hs:3:29:
-    Couldn't match expected type ‘Char’ with actual type ‘Int’
-    In the expression: (10 :: Int)
-    In the first argument of ‘length’, namely ‘['a' .. (10 :: Int)]’
-    In the first argument of ‘print’, namely
-      ‘(length ['a' .. (10 :: Int)])’
+overloadedlistsfail05.hs:3:24: error:
+    • Couldn't match type ‘Char’ with ‘Int’
+      Expected type: GHC.Exts.Item [Int]
+        Actual type: Char
+    • In the expression: 'a'
+      In the first argument of ‘length’, namely
+        ‘(['a' .. (10 :: Int)] :: [Int])’
+      In the first argument of ‘print’, namely
+        ‘(length (['a' .. (10 :: Int)] :: [Int]))’