fomoscript

Toy scripting language, built with Rust

0 dependencies*
1 file
no_std with alloc

Only a few days old. Not production ready. The goal is to use it in Fomos as a shell.

* except log, doesn't count ;)

Examples

Simple script

{
    let x = 0
    while x<5 {
        x = x+1
    }
    x
}

returns 5

Support of higher order functions

{
    let x = 0
    let f = (e) => {e+1}
    let g = (f,e) => f(e)
    g(f,x)
}

returns 1

Use in Rust

Step 1: have some code

let code: Vec<char> = r#"
{
    let x = 0
    while x<5 {
        x = x+1
    }
    x
}"#
    .chars()
    .collect();

Step 2: parse it

let ast = parse_ast(&code).expect("parse ok");

Step 3: run it

let mut ctx = Ctx::new(ast);
let result = eval(&0, &mut ctx);

The result will have this type.

Go see the tests for more examples.

By default, there is no side effect possible from the script during eval (except inside ctx)

You can insert native rust closure with (or without) side effects into the script, and use it from there. Example with the print function:

let code: Vec<char> = r#"
{
    my_print(1+1)
}
"#
.chars()
.collect();
let ast = parse_ast(&code).unwrap();
let mut ctx = Ctx::new(ast);

let print_closure = Rc::new(|a: N, _, _, _| {
    println!("{}", a.to_str());
    N::Unit
});
ctx.set_var_absolute("my_print", N::FuncNativeDef(Native(print_closure)));

let _ = eval(&0, &mut ctx);

Cruelly missing

Arrays
Months of work
Pattern matching
Javascript-like objects (we just have Number and String 😱)
Read-Eval-Print Loop
Error handling (now it just UB if something goes wrong)
Escape characters in quoted strings
Operator precedence