On 16 March 2011 11:31, Andrew Coppin
The well-known ST monad uses an ingenious hack to make it impossible for distinct ST computations to interact with each other.
Is there a way to do something similar so that I can create "cursors" that reference a (mutable) container, and then write a function that takes two cursor arguments which are statically guaranteed to refer to the same container?
You could define a function: withContainer ∷ (∀ s. Container s → α) → α which creates a container, parameterizes it with an 's' that is only scoped over the continuation and applies the continuation to the created container. If you then define a function to create a cursor from it like: cursor ∷ Container s → Cursor s it is statically guaranteed that two Cursors parameterized with the same 's' refer to the same container: foo ∷ Cursor s → Cursor s → ... because the only way to create a Container s is through withContainer. Regards, Bas