I’m building out sparse matrix stuff for stan math and would like to make a branch with a `sparse_matrix`

type in stan3. Is that reasonably feasable?

Looking over some of the code it looks like I would have to

- Add
`sparse_matrix`

to stuff in`lexer.mll`

,`parser.mly`

and a bunch of other places? - Add (???) to
`Statement_gen.ml`

- ???
- Sparse Matrix!

I started reading over how ocaml works and the ast/Mir/Stan_math functions.

Can I start hacking away or should I first make the proposal spec?