comment in front of haddock messes up parsing

This seems to be a problem with the grammar itself, as the code: ``` -- Comment -- | Test what f :: Int ``` Has the concrete syntax tree of: ``` (haskell (comment) declarations: (declarations (signature name: (variable) :: type: (name)))) ``` Here you can see there is no 'docstring' element popping up. The code: ``` -- | Test what f :: Int ``` Has concrete syntax tree of: ``` (haskell (haddock) declarations: (declarations (signature name: (variable) :: type: (name)))) ``` which is correct as it has (haddock). I will make a issue of this in haskell grammar