yes-lang

Yet anothEr Scripting Language

Simple interpreter in Rust:

• "manual" tokenization
• single-/multi-line comments
• prefix & infix operators
• Pratt parser impl
• tree-walking interpreter
• immutable scope-based bindings
• functions as a first class citizens
• lexer, parser, interpreter & REPL in <2k LoC

Goals:

• learn by doing
• easy to understand
• easy to implement
• easy to follow
• test coverage

Non-goals:

• IO
• stdlib
• safety
• collections
• performance
• type-safety
• production-readiness
• usability in general

REPL

$ cargo run
[...]
REPL: enter :q to quit.
> let hi = fn(name) { "hello " + name };
[AST]
<function>
> hi("world")
[AST]
hello world
> :q
$

Run

// examples/fib.yes

fn fib1(n, a, b) {
    if n == 0 { a+b }
    else { fib1(n-1, a+b, a) }
}

fn fib(n) {
    if n <= 0 { 0 }
    else {
        if n <= 2 { 1 }
        else {
            fib1(n-2, 1, 0)
        }
    }
}

fib(42) == 267914296 && fib(84) == 160500643816367088

$ cargo run examples/fib.yes
[...]
true