Hi all, Suppose I have a datatype: data Foo a = Foo { int :: a Int, char :: a Char } where I start off with (Foo Nothing Nothing) :: Foo Maybe, gradually accumulate values until I have (Foo (Just 5) (Just 'c')), and then I want to remove the Maybe type so I can lose all the now-redundant Just constructors. Well, suppose in actual fact I prefer the name "CanBe" to Maybe. Then for the first part I want type CanBe a = Maybe a foo :: Foo CanBe foo = ... but of course this fails because CanBe is a non-fully-applied type synonym in "foo :: Foo CanBe", and I can fix this by eta-reducing thus: type CanBe = Maybe foo :: Foo CanBe foo = ... Now for the second part I want type Id a = a foo' :: Foo Id foo' = ... but again Id is not fully applied. However, this time I cannot eta-reduce it! "type Id =" is a parse error, as is "type Id". I'd really like to be able to define an eta-reduced Id; I see two possibilities: * Allow "type Id =" (I prefer this to "type Id" as I think we are more likely to want to use the latter syntax for something else later on). * Implementations should eta-reduce all type synonyms as much as possible, e.g. type T a b c d = X a b Int c d is equivalent to type T a b = X a b Int and type Id a = a is equivalent to a type that cannot be expressed directly. Any opinions? Thanks Ian