Refactor handling of parens in types (#874)

* Fix type parenthesization in Hoogle backend

Ported the logic in the HTML and LaTeX backends for adding in parens
into something top-level in 'GhcUtil'. Calling that from the Hoogle
backend fixes #873.

* Remove parenthesizing logic from LaTeX and XHTML backends

Now, the only times that parenthesis in types are added in any backend
is through the explicit 'HsParTy' constructor. Precedence is also
represented as its own datatype.

* List out cases explicitly vs. catch-all

* Fix printing of parens for QuantifiedConstraints

The priority of printing 'forall' types was just one too high.

Fixes #877.

* Accept HTML output for quantified contexts test

1 files changed, 26 insertions, 0 deletions

diff --git a/hoogle-test/ref/Bug873/test.txt b/hoogle-test/ref/Bug873/test.txt
new file mode 100644
index 00000000..19100212
--- /dev/null
+++ b/hoogle-test/ref/Bug873/test.txt
@@ -0,0 +1,26 @@
+-- Hoogle documentation, generated by Haddock
+-- See Hoogle, http://www.haskell.org/hoogle/
+
+@package test
+@version 0.0.0
+
+module Bug873
+
+-- | Application operator. This operator is redundant, since ordinary
+--   application <tt>(f x)</tt> means the same as <tt>(f <a>$</a> x)</tt>.
+--   However, <a>$</a> has low, right-associative binding precedence, so it
+--   sometimes allows parentheses to be omitted; for example:
+--   
+--   <pre>
+--   f $ g $ h x  =  f (g (h x))
+--   </pre>
+--   
+--   It is also useful in higher-order situations, such as <tt><a>map</a>
+--   (<a>$</a> 0) xs</tt>, or <tt><a>zipWith</a> (<a>$</a>) fs xs</tt>.
+--   
+--   Note that <tt>($)</tt> is levity-polymorphic in its result type, so
+--   that foo $ True where foo :: Bool -&gt; Int# is well-typed
+($) :: () => (a -> b) -> a -> b
+infixr 0 $
+($$) :: (a -> b) -> a -> b
+infixr 0 $$