diff options
Diffstat (limited to 'compiler/types/TyCon.hs')
| -rw-r--r-- | compiler/types/TyCon.hs | 26 |
1 files changed, 20 insertions, 6 deletions
diff --git a/compiler/types/TyCon.hs b/compiler/types/TyCon.hs index cdfcf181a5..54a57cfc45 100644 --- a/compiler/types/TyCon.hs +++ b/compiler/types/TyCon.hs @@ -358,13 +358,27 @@ Note [Unboxed tuple RuntimeRep vars] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The contents of an unboxed tuple may have any representation. Accordingly, the kind of the unboxed tuple constructor is runtime-representation -polymorphic. For example, +polymorphic. + +Type constructor (2 kind arguments) + (#,#) :: forall (q :: RuntimeRep) (r :: RuntimeRep). + TYPE q -> TYPE r -> TYPE (TupleRep [q, r]) +Data constructor (4 type arguments) + (#,#) :: forall (q :: RuntimeRep) (r :: RuntimeRep) + (a :: TYPE q) (b :: TYPE r). a -> b -> (# a, b #) + +These extra tyvars (q and r) cause some delicate processing around tuples, +where we need to manually insert RuntimeRep arguments. +The same situation happens with unboxed sums: each alternative +has its own RuntimeRep. +For boxed tuples, there is no levity polymorphism, and therefore +we add RuntimeReps only for the unboxed version. + +Type constructor (no kind arguments) + (,) :: Type -> Type -> Type +Data constructor (2 type arguments) + (,) :: forall a b. a -> b -> (a, b) - (#,#) :: forall (q :: RuntimeRep) (r :: RuntimeRep). TYPE q -> TYPE r -> # - -These extra tyvars (v and w) cause some delicate processing around tuples, -where we used to be able to assume that the tycon arity and the -datacon arity were the same. Note [Injective type families] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |