On Tue, 24 Jun 2014, Simon Peyton Jones wrote:
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.
I think I've figured out what might be causing the problem.
First, a couple figures. With these rules:
pattern_synonym_decl
: 'pattern' con vars0 patsyn_token pat
| 'pattern' varid conop varid patsyn_token pat
pattern_synonym_sig
: 'pattern' patsyn_stuff '::' ctype
patsyn_stuff
: constr_stuff
I'm getting 112 new reduce/reduce conflicts.
If I add the context like you recommended:
pattern_synonym_sig
: 'pattern' patsyn_context patsyn_stuff '::' ctype
patsyn_context :: { LHsContext RdrName }
: forall
| forall context '=>'
then I get 54 new shift/reduce conflicts and no (new) reduce/reduce
conflicts.
My feeling is the problem is that patterns don't need any special
parentheses around type annotations, which means the following is a legal
pattern synonym definition:
pattern Single x = [x] :: [Int]
and I think that the difference (the '=' or '<-') is too 'deep' between
this and something like
pattern Single a :: [a]
Unfortunately, I still have no idea how to solve this problem...
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