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
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