What do you mean by "doesn't work"? Crashes? Fails to build with some error? Builds but doesn't parse what you expect? In the latter case, what happened to the shift/reduce and reduce/reduce errors reported by Happy? Esp the latter. If you are getting more you need to track them down. For exmape if I see pattern P ... and I've gotten to the P. Have I seen an empty forall, and this is the beginning of context, or have I seen an empty patsyn_context, and this is the beginning of constr_stuff. I think this'll be a reduce/reduce error. I think it may be helped by patsyn_contxt :: forall | forall context '=>' c.f the defn of 'constr'. IN haste Simoin | -----Original Message----- | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Dr. | ERDI Gergo | Sent: 24 June 2014 13:12 | To: GHC Devs | Subject: Help needed: parsing pattern synonym contexts | | 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 | _______________________________________________ | ghc-devs mailing list | ghc-devs@haskell.org | http://www.haskell.org/mailman/listinfo/ghc-devs