Binary instance for Static Pointers - haskell

Question

I have the following data type
data Foo a b = A (StaticPtr (a -> b)) deriving (Generic, Typeable)
I want to generate the Binary instance for this type so I can use this function on a remote node.
However, using automatic Binary instantiation doesn't work here:
instance (Binary a, Binary b) => Binary (Foo a b)
This results in
• Could not deduce (Binary (StaticPtr (a -> b)))
arising from a use of ‘binary-0.8.5.1:Data.Binary.Class.$dmput’
from the context: (Binary a, Binary b)
bound by the instance declaration
at /Users/abhiroop/Haskell/snape/app/Spec.hs:23:10-49
• In the expression:
binary-0.8.5.1:Data.Binary.Class.$dmput #Foo a b
In an equation for ‘binary-0.8.5.1:Data.Binary.Class.put’:
binary-0.8.5.1:Data.Binary.Class.put
= binary-0.8.5.1:Data.Binary.Class.$dmput #Foo a b
In the instance declaration for ‘Binary (Foo a b)’
• Could not deduce (Binary (StaticPtr (a -> b)))
arising from a use of ‘binary-0.8.5.1:Data.Binary.Class.$dmget’
from the context: (Binary a, Binary b)
bound by the instance declaration
at /Users/abhiroop/Haskell/snape/app/Spec.hs:23:10-49
• In the expression:
binary-0.8.5.1:Data.Binary.Class.$dmget #Foo a b
In an equation for ‘binary-0.8.5.1:Data.Binary.Class.get’:
binary-0.8.5.1:Data.Binary.Class.get
= binary-0.8.5.1:Data.Binary.Class.$dmget #Foo a b
In the instance declaration for ‘Binary (Foo a b)’
How do I auto generate the Binary instance here?

Answer 1

You can serialize a StaticPtr as a Fingerprint via staticKey and deserialize it via unsafeLookupStaticPtr below it.
You can't define a Binary instance for StaticPtr (even if you wrap it in a newtype to avoid orphans) because the lookup cannot be done purely. But you can still define and use the serializer and deserializer as regular, nonoverloaded functions.

Answer 2

Li-yao Xia's answer is correct. But I had to change my data types, in general, to pass them remotely. I am writing my changes here so it might be useful if someone wants to send a function remotely, there isn't many resources on this online.
So instead of having
data Foo a b = A (StaticPtr (a -> b))
I have changed my data types to look like this:
data Foo a b = A (a -> b)
or to simplify
data Foo f = A f
Here f is the function I want to send remotely.
So taking a simple example of a function like (+ 1) and imagine I want to map this over a list [1,2,3] which is present remotely. My code becomes like this:
main :: IO [Int]
main = do
let list = [1,2,3]
a = static (A (+ 1)) :: StaticPtr (Foo (Int -> Int))
t = staticKey a
-- assuming you sent t to the remote node
-- code on the remote node
x <- unsafeLookupStaticPtr t
case x of
Just sptr -> case deRefStaticPtr sptr of
A f -> return $ map f list
_ -> error "Task undefined"
Nothing -> error "Wrong function serialized"