Recursive data types

Currently, `deftype` doesn't seem to support recursive data types:

(deftype SExpr (Number [Int]) (List [(Array SExpr)]))

This makes sense, because in general recursive data types could make the C struct "infinitely large"; at least, without putting the recursive values on the heap explicitly.

However, since I don't think one can currently put a value on the heap explicitly in Carp (barring manual use of `malloc`/`free`), and since anyway it seems this fails in the parser already, I don't think it's possible to define an s-expression type like the above in Carp.

Is such a feature planned? Am I misunderstanding something?

The issue names no files or tests; begin by reproducing the `deftype` example and tracing where recursive data types are rejected by the parser. Determine whether recursive values can be represented without infinitely sized C structs, then define the feature's accepted syntax and behavior before implementation.

Written by the indexing model from the issue text.