Close - it compiles now! I made a minor change, going to Typeable1 instead of Typeable:
instance (Typeable1 f, Typeable1 g) => Typeable1 (f :+: g) where
typeOf1 l@(Inl x) = mkTyConApp (mkTyCon "Planning.Wouter.:+:")
[typeOf1 x, typeOf1 y]
where (Inr y) = undefined `asTypeOf` l
typeOf1 r@(Inr y) = mkTyConApp (mkTyCon "Planning.Wouter.:+:")
[typeOf1 x, typeOf1 y]
where (Inl x) = undefined `asTypeOf` r
Except this gives me a runtime error:
*WouterTest> getName testNamed
"*** Exception: Prelude.undefined
The only thing I can think of is to have a class that gives default
values to type - ick!
-Ron Alford
On Thu, Jul 10, 2008 at 4:16 PM, Antoine Latter <[EMAIL PROTECTED]> wrote:
> On Thu, Jul 10, 2008 at 2:15 PM, Ron Alford <[EMAIL PROTECTED]> wrote:
>> I'm making progress, but how would I make the following a Typeable instance:
>> data (f :+: g) e = Inl (f e) | Inr (g e) deriving Eq
>>
>> Here is what I'm using for Expr:
>> data Expr f = In (f (Expr f))
>> instance Typeable1 f => Typeable (Expr f) where
>> typeOf (In x) = mkTyConApp (mkTyCon "Data.Trie.General.ListGT") [typeOf1
>> x]
>>
>> I don't think I can use this for ':+:', because the typeOf instance
>> only has access to a member of one type at a time.
>> This may be similar to a definition of Typeable2 for Either, but I
>> can't find an example to follow for that.
>>
>
> Maybe something like:
>
> instance (Typeable1 f, Typeable1 g) => Typeable (f :+: g) where
> typeOf in@(InL f) = (some function of 'f' and 'g')
> where InR g = undefined `asTypeOf` in
>
> typeOf in@(InR g) = (some function of 'f' and 'g')
> where InL f = undefined `asTypeOf` in
>
> would work?
>
> -Antoine
>
WouterTest.hs
Description: Binary data
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