Support value/type namespaces on identifier links

Identifier links can be prefixed with a 'v' or 't' to indicate the value or
type namespace of the desired identifier. For example:

-- | Some link to a value: v'Data.Functor.Identity'
--
-- Some link to a type: t'Data.Functor.Identity'

The default is still the type (with a warning about the ambiguity)

1 files changed, 10 insertions, 0 deletions

diff --git a/doc/markup.rst b/doc/markup.rst
index 9fb0209a..48a6f4ad 100644
--- a/doc/markup.rst
+++ b/doc/markup.rst
@@ -913,6 +913,16 @@ If ``M.T`` is not otherwise in scope, then Haddock will simply emit a
 link pointing to the entity ``T`` exported from module ``M`` (without
 checking to see whether either ``M`` or ``M.T`` exist).
 
+Since values and types live in different namespaces in Haskell, it is
+possible for a reference such as ``'X'`` to be ambiguous. In such a case,
+Haddock defaults to pointing to the type. The ambiguity can be overcome by explicitly specifying a namespace, by way of a ``v`` (for value) or ``t``
+(for type) immediately before the link: ::
+
+    -- | An implicit reference to  'X', the type constructor
+    --   An explicit reference to v'X', the data constructor
+    --   An explicit reference to t'X', the type constructor
+    data X = X
+
 To make life easier for documentation writers, a quoted identifier is
 only interpreted as such if the quotes surround a lexically valid
 Haskell identifier. This means, for example, that it normally isn't