properly highlight magic hashes in type signatures

Author: raichoo

syntax/haskell.vim

@@ -25,7 +25,7 @@ syn match haskellRecordField contained containedin=haskellBlock
   \ haskellSeparator,
   \ haskellParens
 syn match haskellTypeSig
-  \ "^\s*\(where\s\+\|let\s\+\|default\s\+\)\?[_a-z][a-zA-Z0-9_']*\(,\s*[_a-z][a-zA-Z0-9_']*\)*\_s\+::\s"
+  \ "^\s*\(where\s\+\|let\s\+\|default\s\+\)\?[_a-z][a-zA-Z0-9_']*#\?\(,\s*[_a-z][a-zA-Z0-9_']*#\?\)*\_s\+::\s"
   \ contains=
   \ haskellWhere,
   \ haskellLet,