Constructors
------------

    func new(arena a) -> ref var Thing
        lifetime return == a                # <-- an "==" relation needs to be added
    {
        ref var Thing obj = alloc{.x=123, .y=true}  # <-- an "alloc" keyword needs to be added
        obj.init_stuff()
        return obj
    }


The "alloc" keyword
-------------------

Allocation in the "default" arena (of the "this" parameter,
or in non-methods, of the first parameter):

    ref var Thing t = alloc                     #<-- unintialized allocation
    ref var Thing t = alloc {.x=123, .y=true}   #<-- initialized struct alloc
    ref var [4]int = alloc [1,2,3,4]            #<-- initialized array alloc

Allocation in an explicit arena:

    ref var Thing t = alloc ar
    ref var Thing t = alloc ar {.x=123, .y=true}
    ref var [4]int = alloc ar [1,2,3,4]

Parsing:

* No newline is allowed before the ( { [