# MOM , Minimal Object Machine

This layer sits between the language layer (vool) and the risc machine layer.
It is meant to make the transition (between vool and risc) easier to understand.

Previous efforts were doing the transition without an intermediate layer. But while
this was possible, it was more difficult than need be, and so we go to the old saying
that everything in computing can be fixed by another layer :-)

## Recap

A little recap of why the transition was too steep will naturally reveal the design of MOM.

### Structure

Vool has a tree structure. Risc is a linked list, so essentially flat.

### Memory model

Vool has no memory, it has objects and they just are. Risc on the other hand has only registers
and memory. Data can only move to/from/between registers, ie not from memory to memory.
While Risc knows about objects, it deals in machine words.

### Execution model

Vool's implicit execution model would be interpretation, ie tree traversal. Vool has high level
control structures, including send, and no goto, it is a language after all.

Risc is close to a cpu, it has a current instruction (pc), registers (8) and a register based
instruction set. Risc has word comparisons and a jump. Call is not used as the stack is not
used (stacks are messy, not oo)

## Design

The *essential* step from vool to risc, is the one from a language to a machine. From statements
that hang in the air, to an instruction set.
So to put a layer in the middle of those two, MOM will be:

### Tree based

So almost 1-1 from vool (leave that transformation for next step, which is part of the
simplification. Flattening needs state to be carried around and so we can do without that)

### Use object memory

object to object transfer

no registers

### Instruction based

So a machine rather than a language. No control structures, but compare and jump instructions.

No send or call, just objects and jump.

Machine capabilities (instructions) for basic operations. Use of macros for higher level.

## Outlook

The next transformation from mom to the Risc layer will naturally include the transformation of:
- tree to list
- mom instructions to risc instructions (which is 1 to n so relatively simple)
- memory to memory transfer, to memory register memory transfers.