Commit bee517d2 authored by simonpj@microsoft.com's avatar simonpj@microsoft.com

Tighten up what it means to be an "enumeration data constructor"

See Note [Enumeration types] in TyCon, and comments in Trac #4528
parent 35a77384
......@@ -112,10 +112,14 @@ mkDataTyConRhs :: [DataCon] -> AlgTyConRhs
mkDataTyConRhs cons
= DataTyCon {
data_cons = cons,
is_enum = not (null cons) &&
all isNullarySrcDataCon cons
is_enum = not (null cons) && all is_enum_con cons
-- See Note [Enumeration types] in TyCon
}
where
is_enum_con con
| (_tvs, theta, arg_tys, _res) <- dataConSig con
= null theta && null arg_tys
mkNewTyConRhs :: Name -> TyCon -> DataCon -> TcRnIf m n AlgTyConRhs
-- ^ Monadic because it makes a Name for the coercion TyCon
......
......@@ -582,7 +582,7 @@ data CoTyConDesc
Note [Enumeration types]
~~~~~~~~~~~~~~~~~~~~~~~~
We define datatypes with no constructors to not be
We define datatypes with no constructors to *not* be
enumerations; this fixes trac #2578, Otherwise we
end up generating an empty table for
<mod>_<type>_closure_tbl
......@@ -590,6 +590,16 @@ which is used by tagToEnum# to map Int# to constructors
in an enumeration. The empty table apparently upset
the linker.
Moreover, all the data constructor must be enumerations, meaning
they have type (forall abc. T a b c). GADTs are not enumerations.
For example consider
data T a where
T1 :: T Int
T2 :: T Bool
T3 :: T a
What would [T1 ..] be? [T1,T3] :: T Int? Easiest thing is to exclude them.
See Trac #4528.
Note [Newtype coercions]
~~~~~~~~~~~~~~~~~~~~~~~~
The NewTyCon field nt_co is a a TyCon (a coercion constructor in fact)
......
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