| Quick question - is it possible to put type class contexts on
| existentially quantified variables in GADTs defined using record syntax?
Audrey Tang implemented the ability to use record syntax for GADTs. Looks as
if she didn't finish. I see the code below in Parser.y.pp. Note the
commented-out code. It looks as if her *intention* was to allow
forall a. Eq a => D { x,y :: a } :: T a
but she didn't do that for some reason. My guess: she got reduce/reduce errors
and never came back to it
In short, I think the only obstacle here is parsing. Would someone like to
have a go? And/or file a feature request?
Simon
-- We allow the following forms:
-- C :: Eq a => a -> T a
-- C :: forall a. Eq a => !a -> T a
-- D { x,y :: a } :: T a
-- forall a. Eq a => D { x,y :: a } :: T a
gadt_constr :: { LConDecl RdrName }
: con '::' sigtype
{ LL (mkGadtDecl $1 $3) }
-- Syntax: Maybe merge the record stuff with the single-case above?
-- (to kill the mostly harmless reduce/reduce error)
-- XXX revisit audreyt
| constr_stuff_record '::' sigtype
{ let (con,details) = unLoc $1 in
LL (ConDecl con Implicit [] (noLoc []) details (ResTyGADT $3)
Nothing) }
{-
| forall context '=>' constr_stuff_record '::' sigtype
{ let (con,details) = unLoc $4 in
LL (ConDecl con Implicit (unLoc $1) $2 details (ResTyGADT $6)
Nothing ) }
| forall constr_stuff_record '::' sigtype
{ let (con,details) = unLoc $2 in
LL (ConDecl con Implicit (unLoc $1) (noLoc []) details
(ResTyGADT $4) Nothing) }
-}
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