todesking/lisp.rs

Lisp in Rust

Lisp in Rust

Just a toy language.

• Basic syntax:
  • Primitive: 42, true
  • Global variable definition: (define x 1)
  • Application: (f x y)
  • If: (if cond then else)
  • Quote: '(1 2 3)
  • Lambda: (lambda (x y . rest) e1 e2) / (lambda rest e1 e2)
  • Modify local variable: (set-local! x 1)(simple value only) / (unsafe-set-local! x '(1 2 3))(unlimited and unsafe)
    • Due to reference-counting based memory management, unsafe operations may produce cyclic reference and memor leakage.
  • Modify global variable: (set-global! x 123)
  • Error handling: (catch-error handler expr) where handler is (lambda (error-kind payload) ...)
  • letrec: (letrec (((var1 arg11 arg12) body1) ((var2 arg21) body2)) expr)
  • Quasiquote: `(1 2 ,x ,@xs)(where x = 3, xs='(4 5 6)) = (1 2 3 4 5 6)
• Tail Call Optimization available
• Predefined functions:
  • Basic arithmetic: +, -, *, /, %, <, <=, >, >=
  • Equality: eq?
  • List operations: cons, list
  • User-controlled error: (error error-kind payload)
  • primitive functions, standard library, additional functions

Usage

cargo run --release to run REPL.

LISP.rs> (define make-counter (lambda () ((lambda (x) (lambda () (set-local! x (+ 1 x)) x)) 0)))
     => ()
LISP.rs> (define counter-1 (make-counter))
     => ()
LISP.rs> (define counter-2 (make-counter))
     => ()
LISP.rs> (counter-1)
     => 1
LISP.rs> (counter-1)
     => 2
LISP.rs> (counter-2)
     => 1
LISP.rs> (counter-1)
     => 3
LISP.rs> (counter-2)
     => 2
LISP.rs> (fib 30) ; predefined function
     => 832040
Elapsed: 4208[ms]

Predefined fib definition:

(define fib (lambda (n)
    (if (eq? n 0) 0
        (if (eq? n 1) 1
            (+ (fib (- n 1)) (fib (- n 2)))))))