Commit 13adf25f authored by simonpj@microsoft.com's avatar simonpj@microsoft.com

Comment on what an "enumeration" type is

parent afe45347
......@@ -112,15 +112,9 @@ mkDataTyConRhs :: [DataCon] -> AlgTyConRhs
mkDataTyConRhs cons
= DataTyCon {
data_cons = cons,
is_enum = -- 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
-- which is used by tagToEnum# to map Int# to constructors
-- in an enumeration. The empty table apparently upset
-- the linker.
not (null cons) &&
is_enum = not (null cons) &&
all isNullarySrcDataCon cons
-- See Note [Enumeration types] in TyCon
}
mkNewTyConRhs :: Name -> TyCon -> DataCon -> TcRnIf m n AlgTyConRhs
......
......@@ -440,7 +440,7 @@ data AlgTyConRhs
-- (see the tag assignment in DataCon.mkDataCon)
is_enum :: Bool -- ^ Cached value: is this an enumeration type?
-- (See 'isEnumerationTyCon')
-- See Note [Enumeration types]
}
-- | Information about those 'TyCon's derived from a @newtype@ declaration
......@@ -580,6 +580,16 @@ data CoTyConDesc
| CoUnsafe
\end{code}
Note [Enumeration types]
~~~~~~~~~~~~~~~~~~~~~~~~
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
which is used by tagToEnum# to map Int# to constructors
in an enumeration. The empty table apparently upset
the linker.
Note [Newtype coercions]
~~~~~~~~~~~~~~~~~~~~~~~~
The NewTyCon field nt_co is a a TyCon (a coercion constructor in fact)
......@@ -983,6 +993,7 @@ isGadtSyntaxTyCon _ = False
-- | Is this an algebraic 'TyCon' which is just an enumeration of values?
isEnumerationTyCon :: TyCon -> Bool
-- See Note [Enumeration types] in TyCon
isEnumerationTyCon (AlgTyCon {algTcRhs = DataTyCon { is_enum = res }}) = res
isEnumerationTyCon (TupleTyCon {tyConArity = arity}) = arity == 0
isEnumerationTyCon _ = False
......
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