Commit d9b0be3c authored by Simon Peyton Jones's avatar Simon Peyton Jones

Comments in rejigConRes

parent 2d68aa65
......@@ -1323,11 +1323,13 @@ rejigConRes tmpl_tvs res_ty dc_tvs ResTyH98
= (tmpl_tvs, dc_tvs, [], res_ty)
-- In H98 syntax the dc_tvs are the existential ones
-- data T a b c = forall d e. MkT ...
-- The {a,b,c} are tc_tvs, and {d,e} are dc_tvs
-- The universals {a,b,c} are tc_tvs, and the existentials {d,e} are dc_tvs
rejigConRes tmpl_tvs res_tmpl dc_tvs (ResTyGADT _ res_ty)
-- E.g. data T [a] b c where
-- MkT :: forall x y z. T [(x,y)] z z
-- The {a,b,c} are the tmpl_tvs, and the {x,y,z} are the dc_tvs
-- (NB: unlike the H98 case, the dc_tvs are not all existential)
-- Then we generate
-- Univ tyvars Eq-spec
-- a a~(x,y)
......@@ -1340,7 +1342,10 @@ rejigConRes tmpl_tvs res_tmpl dc_tvs (ResTyGADT _ res_ty)
Just subst = tcMatchTy (mkVarSet tmpl_tvs) res_tmpl res_ty
-- This 'Just' pattern is sure to match, because if not
-- checkValidDataCon will complain first.
-- See Note [Checking GADT return types]
-- But care: this only works if the result of rejigConRes
-- is not demanded until checkValidDataCon has
-- first succeeded
-- See Note [Checking GADT return types]
-- /Lazily/ figure out the univ_tvs etc
-- Each univ_tv is either a dc_tv or a tmpl_tv
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