Pointers to ADTs in Haskell

I would like to implement term graphs in Haskell, so that I can implement a term rewriting engine that uses sharing. Something like

data TG f v = Var v | Op f [TG f v] | P (Ptr (TG f v))

And I would want something like the following to make sense:

let
    t' = Op 'f' [Var 'x', Var 'y']
    t = getPointer t'
in
    Op 'g' [P t,P t]

Then during rewriting, I only have to rewrite t once.

However, I noticed two things: (1) the module is called Foreign.Storable, so should it only be used for FFI stuff and (2) there are no instances of Foreign.Storable for any types like lists; why is this?

Pointers to ADTs in Haskell

1 Answers