-- | Concatenate a list of 'Doc's, putting breakable spaces
-- between them.
(<+>) :: Doc -> Doc -> Doc
(<+>) x y = if isEmpty x
               then y
               else if isEmpty y
                    then x
                    else x <> space <> y
(<+>) :: Doc -> Doc -> Doc
(<+>) x y = if isEmpty x
               then y
               else if isEmpty y
                    then x
                    else x <> space <> y
(<+>) x y = if isEmpty x
               then y
               else if isEmpty y
                    then x
                    else x <> space <> y