Future plans:
* Default-constructing (no arguments, zero-initialization) primitive types & struct types
* Introduce type checking & inference as a separate pre-execution/compilation AST pass + add type information into expression nodes
* Pointers: pointer types, address-of operator (&), dereferencing, scope-based lifetime tracking in interpreter
* Function overloading: separate functions from values (again) in interpreter, allow casting to specific function type to take function value
* C FFI: `foreign func sin(x : f32) -> f32`
* Const propagation: annotate expression AST nodes that are computable in compile-time
* Generic parameters: can be either values or `t : type`, but always compile-time
* Generic structs: `struct <t : type, n : u64> array:`, require explicitly specifying parameters when instantiated (used as a type or creating a value)
* Generic functions: `func <t : type, n : u64> max(a : t[n]):`, require explicitly specifying parameters when called or converted to function pointer
* Generic parameter inference for functions & structs
* Extension functions: operator overloading, destructors, iterators & for loop, move assignment (replaces built-in copy)
* Metaprogramming: assigning types to variables (of type `type`), functions can take `type` as regular arguments and return `type`, all type computations are compile-time only

Backlog:
* Mutually recursive functions
* Default-constructing primitive types
* Empty array expression
* Calling functions as methods