Print singleton consraints without parens

The main change is in TypeRep.pprTheta, so we print
       Eq a
for a singleton, but
      (Eq a, Show a)
for multiple constraints.

There are lots of trivial knock-on changes to error messages

1 files changed, 14 insertions, 14 deletions

diff --git a/testsuite/tests/typecheck/should_fail/T9109.stderr b/testsuite/tests/typecheck/should_fail/T9109.stderr
index 3f5236b778..1c7e6e5c09 100644
--- a/testsuite/tests/typecheck/should_fail/T9109.stderr
+++ b/testsuite/tests/typecheck/should_fail/T9109.stderr
@@ -1,14 +1,14 @@
-

-T9109.hs:8:13:

-    Couldn't match expected type ‘t’ with actual type ‘Bool’

-      ‘t’ is untouchable

-        inside the constraints (t1 ~ Bool)

-        bound by a pattern with constructor: GBool :: G Bool,

-                 in an equation for ‘foo’

-        at T9109.hs:8:5-9

-      ‘t’ is a rigid type variable bound by

-          the inferred type of foo :: G t1 -> t at T9109.hs:8:1

-    Possible fix: add a type signature for ‘foo’

-    Relevant bindings include foo :: G t1 -> t (bound at T9109.hs:8:1)

-    In the expression: True

-    In an equation for ‘foo’: foo GBool = True

+
+T9109.hs:8:13:
+    Couldn't match expected type ‘t’ with actual type ‘Bool’
+      ‘t’ is untouchable
+        inside the constraints: t1 ~ Bool
+        bound by a pattern with constructor: GBool :: G Bool,
+                 in an equation for ‘foo’
+        at T9109.hs:8:5-9
+      ‘t’ is a rigid type variable bound by
+          the inferred type of foo :: G t1 -> t at T9109.hs:8:1
+    Possible fix: add a type signature for ‘foo’
+    Relevant bindings include foo :: G t1 -> t (bound at T9109.hs:8:1)
+    In the expression: True
+    In an equation for ‘foo’: foo GBool = True