Some tidying up of type pretty-printing

Triggered by the changes in #13677, I ended up doing a bit of
refactoring in type pretty-printing.

* We were using TyOpPrec and FunPrec rather inconsitently, so
  I made it consisent.

* That exposed the fact that we were a bit undecided about whether
  to print
     a + b -> c + d   vs   (a+b) -> (c+d)
  and similarly
     a ~ [b] => blah  vs   (a ~ [b]) => blah

  I decided to make TyOpPrec and FunPrec compare equal
  (in BasicTypes), so (->) is treated as equal precedence with
  other type operators, so you get the unambiguous forms above,
  even though they have more parens.

  We could readily reverse this decision.
  See Note [Type operator precedence] in BasicTypes

* I fixed a bug in pretty-printing of HsType where some
  parens were omitted by mistake.

7 files changed, 19 insertions, 18 deletions

diff --git a/testsuite/tests/haddock/haddock_examples/haddock.Test.stderr b/testsuite/tests/haddock/haddock_examples/haddock.Test.stderr
index 8f06390348..49618904a2 100644
--- a/testsuite/tests/haddock/haddock_examples/haddock.Test.stderr
+++ b/testsuite/tests/haddock/haddock_examples/haddock.Test.stderr
@@ -151,26 +151,26 @@ data Ex a
     Ex4 (forall a. a -> a)
 <document comment>
 k ::
-  T () ()  This argument has type 'T'
-  -> (T2 Int Int)  This argument has type 'T2 Int Int'
-     -> (T3 Bool Bool
-         -> T4 Float Float)  This argument has type @T3 Bool Bool -> T4 Float Float@
-        -> T5 () ()  This argument has a very long description that should
+  (T () ()  This argument has type 'T')
+  -> ((T2 Int Int)  This argument has type 'T2 Int Int')
+     -> ((T3 Bool Bool
+          -> T4 Float Float)  This argument has type @T3 Bool Bool -> T4 Float Float@)
+        -> (T5 () ()  This argument has a very long description that should
  hopefully cause some wrapping to happen when it is finally
- rendered by Haddock in the generated HTML page.
+ rendered by Haddock in the generated HTML page.)
            -> IO ()  This is the result type
-l :: (Int, Int, Float)  takes a triple -> Int  returns an 'Int'
+l :: ((Int, Int, Float)  takes a triple) -> Int  returns an 'Int'
 <document comment>
 m ::
-  R -> N1 ()  one of the arguments -> IO Int  and the return value
+  R -> (N1 ()  one of the arguments) -> IO Int  and the return value
 <document comment>
 newn ::
-  R  one of the arguments, an 'R'
-  -> N1 ()  one of the arguments -> IO Int
+  (R  one of the arguments, an 'R')
+  -> (N1 ()  one of the arguments) -> IO Int
 newn = undefined
 <document comment>
 foreign import ccall unsafe "header.h" o
-  :: Float  The input float -> IO Float  The output float
+  :: (Float  The input float) -> IO Float  The output float
 <document comment>
 newp :: Int
 newp = undefined
diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA023.stderr b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA023.stderr
index 63c2b2f74b..c0233de0d5 100644
--- a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA023.stderr
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA023.stderr
@@ -1,7 +1,7 @@
 
 ==================== Parser ====================
 module ShouldCompile where
-test :: (Eq a) => [a]  doc1 -> [a]  doc2  -> [a]  doc3
+test :: (Eq a) => ([a]  doc1) -> ([a]  doc2 ) -> [a]  doc3
 test xs ys = xs
 
 
diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA024.stderr b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA024.stderr
index b3caa71b9e..f1db2374b1 100644
--- a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA024.stderr
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA024.stderr
@@ -1,7 +1,7 @@
 
 ==================== Parser ====================
 module ShouldCompile where
-test2 :: a  doc1  -> b  doc2  -> a  doc 3 
+test2 :: (a  doc1 ) -> (b  doc2 ) -> a  doc 3 
 test2 x y = x
 
 
diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA025.stderr b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA025.stderr
index 472ec1a1eb..4b208f858a 100644
--- a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA025.stderr
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA025.stderr
@@ -1,7 +1,7 @@
 
 ==================== Parser ====================
 module ShouldCompile where
-test2 :: a  doc1  -> a
+test2 :: (a  doc1 ) -> a
 test2 x = x
 
 
diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA026.stderr b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA026.stderr
index 769da3f0d3..fcf9e0c2d6 100644
--- a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA026.stderr
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA026.stderr
@@ -1,7 +1,8 @@
 
 ==================== Parser ====================
 module ShouldCompile where
-test :: (Eq a) => [a]  doc1 -> forall b. [b]  doc2  -> [a]  doc3
+test ::
+  (Eq a) => ([a]  doc1) -> forall b. ([b]  doc2 ) -> [a]  doc3
 test xs ys = xs
 
 
diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA027.stderr b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA027.stderr
index e7707c5ec0..cd8884080f 100644
--- a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA027.stderr
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA027.stderr
@@ -2,9 +2,9 @@
 ==================== Parser ====================
 module ShouldCompile where
 test ::
-  [a]  doc1
+  ([a]  doc1)
   -> forall b.
-     (Ord b) => [b]  doc2  -> forall c. (Num c) => [c]  doc3 -> [a]
+     (Ord b) => ([b]  doc2 ) -> forall c. (Num c) => ([c]  doc3) -> [a]
 test xs ys zs = xs
 
 
diff --git a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA028.stderr b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA028.stderr
index 47d2468ea5..9e1edc661b 100644
--- a/testsuite/tests/haddock/should_compile_flag_haddock/haddockA028.stderr
+++ b/testsuite/tests/haddock/should_compile_flag_haddock/haddockA028.stderr
@@ -2,7 +2,7 @@
 ==================== Parser ====================
 module ShouldCompile where
 data a <--> b = Mk a b
-test :: [a]  doc1  -> a <--> b -> [a]  blabla
+test :: ([a]  doc1 ) -> a <--> b -> [a]  blabla
 test xs ys = xs