Hi, I'm working on adding type signatures to pattern synonyms. The syntax I'm after would look something like, e.g.: pattern (Eq b) => P Int (Bool, b) (f [a]) :: (Show a) => Maybe [a] My problem is with parsing the two contexts. I wrote the parser in the following way, which I felt natural (actions omitted for brevity) pattern_synonym_sig :: { LSig RdrName } : 'pattern' patsyn_context patsyn_stuff '::' patsyn_context type patsyn_stuff :: { Located (Located RdrName, HsPatSynDetails (LHsType RdrName)) } : constr_stuff patsyn_context :: { LHsContext RdrName } : {- empty -} | forall context '=>' However, this doesn't work, no matter if those contexts are present or not. If I remove both contexts from the rules, i.e. if I replace pattern_synonym_sig with : 'pattern' patsyn_stuff '::' type then parsing succeeds when there are no contexts on either side. I've also tried : 'pattern' patsyn_stuff '::' ctype with the intention of recovering the required context from the ctype (and I could do similar tricks to get the provided context from the patsyn_stuff by using a modified version of constr_stuff); however, even that doesn't work as I expected it, i.e. with this latter version, this: pattern Single a :: (Eq a) => [a] fails with a parse error on "::". Can someone help me out here please? Thanks, Gergo