newTyConInstRhs :: TyCon -> [Type] -> Type
-- ^ Unwrap one 'layer' of newtype on a type constructor and its
-- arguments, using an eta-reduced version of the @newtype@ if possible.
-- This requires tys to have at least @newTyConInstArity tycon@ elements.
newTyConInstRhs tycon tys
    = ASSERT2( tvs `leLength` tys, ppr tycon $$ ppr tys $$ ppr tvs )
      applyTysX tvs rhs tys
  where
    (tvs, rhs) = newTyConEtadRhs tycon

{-
---------------------------------------------------------------------
                                SynTy
                                ~~~~~

Notes on type synonyms
~~~~~~~~~~~~~~~~~~~~~~
The various "split" functions (splitFunTy, splitRhoTy, splitForAllTy) try
to return type synonyms wherever possible. Thus

        type Foo a = a -> a

we want
        splitFunTys (a -> Foo a) = ([a], Foo a)
not                                ([a], a -> a)

The reason is that we then get better (shorter) type signatures in
interfaces.  Notably this plays a role in tcTySigs in TcBinds.lhs.


                Representation types
                ~~~~~~~~~~~~~~~~~~~~

Note [Nullary unboxed tuple]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We represent the nullary unboxed tuple as the unary (but void) type
Void#.  The reason for this is that the ReprArity is never
less than the Arity (as it would otherwise be for a function type like
(# #) -> Int).

As a result, ReprArity is always strictly positive if Arity is. This
is important because it allows us to distinguish at runtime between a
thunk and a function takes a nullary unboxed tuple as an argument!
-}
newTyConInstRhs :: TyCon -> [Type] -> Type
newTyConInstRhs tycon tys
    = ASSERT2( tvs `leLength` tys, ppr tycon $$ ppr tys $$ ppr tvs )
      applyTysX tvs rhs tys
  where
    (tvs, rhs) = newTyConEtadRhs tycon

{-
---------------------------------------------------------------------
                                SynTy
                                ~~~~~

Notes on type synonyms
~~~~~~~~~~~~~~~~~~~~~~
The various "split" functions (splitFunTy, splitRhoTy, splitForAllTy) try
to return type synonyms wherever possible. Thus

        type Foo a = a -> a

we want
        splitFunTys (a -> Foo a) = ([a], Foo a)
not                                ([a], a -> a)

The reason is that we then get better (shorter) type signatures in
interfaces.  Notably this plays a role in tcTySigs in TcBinds.lhs.


                Representation types
                ~~~~~~~~~~~~~~~~~~~~

Note [Nullary unboxed tuple]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We represent the nullary unboxed tuple as the unary (but void) type
Void#.  The reason for this is that the ReprArity is never
less than the Arity (as it would otherwise be for a function type like
(# #) -> Int).

As a result, ReprArity is always strictly positive if Arity is. This
is important because it allows us to distinguish at runtime between a
thunk and a function takes a nullary unboxed tuple as an argument!
-}
newTyConInstRhs tycon tys
    = ASSERT2( tvs `leLength` tys, ppr tycon $$ ppr tys $$ ppr tvs )
      applyTysX tvs rhs tys
  where
    (tvs, rhs) = newTyConEtadRhs tycon

{-
---------------------------------------------------------------------
                                SynTy
                                ~~~~~

Notes on type synonyms
~~~~~~~~~~~~~~~~~~~~~~
The various "split" functions (splitFunTy, splitRhoTy, splitForAllTy) try
to return type synonyms wherever possible. Thus

        type Foo a = a -> a

we want
        splitFunTys (a -> Foo a) = ([a], Foo a)
not                                ([a], a -> a)

The reason is that we then get better (shorter) type signatures in
interfaces.  Notably this plays a role in tcTySigs in TcBinds.lhs.


                Representation types
                ~~~~~~~~~~~~~~~~~~~~

Note [Nullary unboxed tuple]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We represent the nullary unboxed tuple as the unary (but void) type
Void#.  The reason for this is that the ReprArity is never
less than the Arity (as it would otherwise be for a function type like
(# #) -> Int).

As a result, ReprArity is always strictly positive if Arity is. This
is important because it allows us to distinguish at runtime between a
thunk and a function takes a nullary unboxed tuple as an argument!
-}