todo.org


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#+title: TODOs
#+author: Aryadev Chavali
#+date: 2023-11-02

* TODO Write a label/jump system :ASM:
Essentially a user should be able to write arbitrary labels (maybe
through ~label x~ or ~x:~ syntax) which can be referred to by ~jump~.

It'll purely be on the assembler side as a processing step, where the
emitted bytecode purely refers to absolute addresses; the VM should
just be dealing with absolute addresses here.
* TODO Allow relative addresses in jumps :ASM:
As requested, a special syntax for relative address jumps.  Sometimes
it's a bit nicer than a label.
* TODO Calling and returning control flow :VM: :ASM:
When writing library code we won't know the addresses of where
callers are jumping from.  However, most library functions want to
return control flow back to where the user had called them: we want
the code to act almost like an inline function.

There are two ways I can think of achieving this:
+ Some extra syntax around labels (something like ~@inline <label>:~)
  which tells the assembly processor to inline the label when a "jump"
  to that label is given
  + This requires no changes to the VM, which keeps it simple, but a
    major change to the assembler to be able to inline code.  However,
    the work on writing a label system and relative addresses should
    provide some insight into how this could be possible.
+ A /call stack/ and two new syntactic constructs ~call~ and ~ret~
  which work like so:
  + When ~call <label>~ is encountered, the next program address is
    pushed onto the call stack and control flow is set to the label
  + During execution of the ~<label>~, when a ~ret~ is encountered,
    pop an address off the call stack and set control flow to that
    address
  + This simulates the notion of "calling" and "returning from" a
    function in classical languages, but requires more machinery on
    the VM side.