Crate baby_emulator

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§Manchester Small-Scale Experimental Machine “Baby” Emulator Library Released API docs MIT licensed

This library provides a collections of types and methods for emulating & assembling code for the Machester Baby, the first program stored computer.


The Manchester “Baby” was the first computer to store both its program code and data in a common randomly-accessible memory, it is for this reason the Baby is considered the first machine to run “true” software, providing a familiar (abeit, primitive) programming environment to anyone familiar with assembly, this library can be included in a variety of software and platforms allowing emulation functionality of this historic machine.

This library provides an interface for emulating the Baby as a bytecode interpreter (baby_emulator::core), and also a library for assembling asm using both modern and original asm notations into a format that can be ran by the emulator (baby_emulator::assmebler).

Please log any questions or issues to the GitHub repo.


Command line:

cargo add baby-emulator 


baby-emulator = "0.2.0" 


This shows a few short examples of what this library is capable of, designed to be a starting point allowing further experimentation by the “user”. See baby_emulator::core and baby_emulator::assembler for further examples and info.

§Bytecode Interpreter Emulation

The core of this library is baby_emulator::core::BabyModel, this struct has fields representing all of the Baby’s internal registers and 32 word memory, you can initialise this struct with an array of [i32; 32], this array can contain the program code instructions starting at position 0.

This example runs an example program that adds 5 to 5 and stores the result in the accumulator. Running here is done with the BabyModel::run_loop method, this method will simply execute sucessive instructions until either an error is thrown (like a stop instruction), or the number os iterations exceeds the specified limmit.

use baby_emulator::core::BabyModel;
use baby_emulator::core::errors::BabyErrors;
use baby_emulator::core::errors::BabyError;
let model = BabyModel::new_example_program();
match model.run_loop(100) {
    (model, BabyErrors::Stop(_)) => println!("{}", model.core_dump()),
    (_, err) => println!("{}", err.get_descriptor())

You can also single set through an emulation, executing a single instruction at a time using the execute method and seeing the direct result.

use baby_emulator::core::BabyModel;
use baby_emulator::core::errors::BabyError;
let model = BabyModel::new_example_program();
match model.execute() {
    Ok(m) => println!("{}", m.core_dump()),
    Err(e) => println!("Error {}", e.get_descriptor())


Here is an example of assembling a Baby asm string using modern notation, then running the resultant program, see the baby_emulator::assembler docs for more information:

use baby_emulator::assembler::{assemble, linker::LinkerData}; 
use baby_emulator::core::{BabyModel, instructions::BabyInstruction};
const ASM: &str = 
ldn $start_value  ; Loads 10 into the accumulator 
:loop_start_value ; The memory address the loop should return to 
sub $subtract_val ; Subtract 1 from the accumulator 
cmp               ; Skip the next jump instruction if the accumulator is negative 
jmp $loop_start   ; Jump to the start of the loop 
stp               ; Program stops when the accumulator is negative 
:loop_start       ; Pointer to the memory address the loop should return to 
abs $loop_start_value
:subtract_val     ; Value to be subtracted
abs 0d1
:start_value ; Value to start in the accumulator 
abs 0d-10
fn main() {
    let instructions = match assemble(&String::from(ASM), false) {
        Ok(LinkerData(v, _)) => v,
        Err(e) => { println!("{}", e.describe(true)); return; }
    let main_store = BabyInstruction::to_numbers(instructions);
    let mut model = BabyModel::new_with_program(main_store);
    loop {
        model = match model.execute() {
            Ok(m) => m,
            Err(_) => break
    println!("{}", model.core_dump());


  • Contains types and functionality for assembling Baby asm.
  • Contains the core models and emulation functionality.