Link to the definitions to themselves

Currently, the definitions already have an anchor tag that allows URLs
with fragment identifiers to locate them, but it is rather inconvenient
to obtain such a URL (so-called "permalink") as it would require finding
the a link to the corresponding item in the Synopsis or elsewhere.  This
commit adds hyperlinks to the definitions themselves, allowing users to
obtain links to them easily.

To preserve the original aesthetics of the definitions, we alter the
color of the link so as to be identical to what it was, except it now
has a hover effect indicating that it is clickable.

Additionally, the anchor now uses the 'id' attribute instead of the
(obsolete) 'name' attribute.

Closes #407

haddock-api/resources/html/Ocean.std-theme/ocean.css

@@ -41,6 +41,9 @@ a[href]:link { color: rgb(196,69,29); }
 a[href]:visited { color: rgb(171,105,84); }
 a[href]:hover { text-decoration:underline; }
 
+a[href].def:link, a[href].def:visited { color: black; }
+a[href].def:hover { color: rgb(78, 98, 114); }
+
 /* @end */
 
 /* @group Fonts & Sizes */

haddock-api/src/Haddock/Backends/Xhtml/Names.hs

@@ -110,16 +110,21 @@ ppName notation name = wrapInfix notation (getOccName name) $ toHtml (getOccStri
 
 
 ppBinder :: Bool -> OccName -> Html
--- The Bool indicates whether we are generating the summary, in which case
--- the binder will be a link to the full definition.
-ppBinder True n = linkedAnchor (nameAnchorId n) << ppBinder' Prefix n
-ppBinder False n = namedAnchor (nameAnchorId n) ! [theclass "def"]
-                        << ppBinder' Prefix n
+ppBinder = ppBinderWith Prefix
 
 ppBinderInfix :: Bool -> OccName -> Html
-ppBinderInfix True n = linkedAnchor (nameAnchorId n) << ppBinder' Infix n
-ppBinderInfix False n = namedAnchor (nameAnchorId n) ! [theclass "def"]
-                             << ppBinder' Infix n
+ppBinderInfix = ppBinderWith Infix
+
+ppBinderWith :: Notation -> Bool -> OccName -> Html
+-- 'isRef' indicates whether this is merely a reference from another part of
+-- the documentation or is the actual definition; in the latter case, we also
+-- set the 'id' and 'class' attributes.
+ppBinderWith notation isRef n =
+  linkedAnchor name ! attributes << ppBinder' notation n
+  where
+    name = nameAnchorId n
+    attributes | isRef     = []
+               | otherwise = [identifier name, theclass "def"]
 
 ppBinder' :: Notation -> OccName -> Html
 ppBinder' notation n = wrapInfix notation n $ ppOccName n