evalit

A toy interpreter.

example

use evalit::{Interpreter, Evaluator};

fn main() {
    let mut env = Environment::new();

    let script = r#"
    fn fib(n) {
        if n <= 0 {
            return 0;
        }
        if n <= 2 {
            return 1;
        }

        return fib(n-1) + fib(n-2);
    }

    let sum = 0;
    for i in 0..=10 {
        sum += fib(i);
    }

    return sum;
    "#;

    let retval = Interpreter::eval_script(script, env).unwrap();

    println!("ret: {:?}", ret); 
    // should output: 
    // ret: Some(143)
}

syntax

primitive type

null

boolean

true, false

integer

$-2^{63}$ ~ $2^{63}$

float

float number, f64.

string

string quote by "

variable

variable name is a string, start with _ or letter, and can contain letter, number, _.

let a;
let a = 1;

expression

1 + 2 * 3;

operator

operator	description
+	add
-	subtract
*	multiply
/	divide
%	remainder
==	equal
!=	not equal
<	less than
<=	less than or equal
>	greater than
>=	greater than or equal
&&	and
||	or
!	not
=	assign
+=	add assign
-=	subtract assign
*=	multiply assign
/=	divide assign
%=	remainder assign
[]	index
.	member
()	call
..	range

control flow

loop statement

loop to repeat.

loop {}

while statement

while to conditional repeat.

while condition {}

for statement

for to iterate.

for i in 0..=10 {}

if statement

if to choose branch.

if condition {} else {}

break statement

break to exist loop.

continue statement

continue to finish one iterate.

return statement

return to return value.

fn item

user defined function

fn fib(n) {
    if n <= 0 {
        return 0;
    }
    if n <= 2 {
        return 1;
    }

    return fib(n-1) + fib(n-2);
}