GitHub - playX18/lisp-in-types: Lisp implemented inside Rust trait system

1 min read Original article ↗

Lisp in Rust trait system.

Limitations

  • Each symbol must be manually declared via defkey!() macro
  • Numbers cannot be negative
  • Numbers are only in range of 0..8192, you can modify build.rs to generate more natural numbers but then you have to run with RUST_MIN_STACK increased.
  • No (defmacro ...)
  • No eval
  • I have not tested it extensively.

Features

  • Recursive functions
  • Global and lexical environments (via let bindings)
  • Function calls
  • apply properly working
  • call/ec

Example

Factorial:

    type DefFac = expr!(defun SymFac (SymN) (if (= SymN 0) 1 (* SymN (SymFac (- SymN 1)))));

    type Global2 = <DefFac as EvalForm<Global1, Lex0>>::GlobalOut;
    type Fac5 = EvalValue<expr!((SymFac 5)), Global2, Lex0>;
    assert_same::<Fac5, N120>();

    println!("(fac 5) => {:?}", <Fac5 as ToRtValue>::to_rt());

call/ec (delimited)

    // call/ec demo (escape continuation, explicit tag):
    // (call/ec cc (lambda (k) (+ 1 (k 5)))) => 5
    defkey!(SymCC, N10);
    defkey!(SymK, N11);
    type CallECExpr = expr!((call/ec SymCC (lambda (SymK) (+ 1 (SymK 5)))));
    type CallECResult = EvalValue<CallECExpr, Global1, Lex0>;
    assert_same::<CallECResult, N5>();
    println!(
        "(call/ec cc (lambda (k) (+ 1 (k 5)))) => {:?}",
        <CallECResult as ToRtValue>::to_rt()
    );