syntax

Sounio Syntax — Anti-Rust Patterns

Sounio LOOKS like Rust but has different syntax and semantics. These are the most common mistakes.

1. NO Semicolons

Sounio statements end WITHOUT semicolons. The parser treats ; as an error.

// WRONG
let x = 5;
// CORRECT
let x = 5

2. var not let mut

Mutable bindings use var. There is no let mut.

// WRONG
let mut x = 10;
// CORRECT
var x = 10

3. &! not &mut

Exclusive (mutable) references use &!T. There is no &mut.

// WRONG
fn set(x: &mut i32) { *x = 5 }
// CORRECT
fn set(x: &!i32) with Mut { *x = 5 }

4. NO Macros

Sounio has no macro system. No ! after function names.

// WRONG
assert!(x > 0)
println!("hello")
vec![1, 2, 3]
// CORRECT
assert(x > 0)
println("hello")
[1, 2, 3]

5. NO Closure Literals

|x| x + 1 does not compile. Use named function references.

// WRONG
let f = |x| x + 1
// CORRECT
fn add_one(x: i64) -> i64 { x + 1 }
let f = add_one

6. Unary Minus Works

Unary minus works on literals, variables and arguments; no 0 - x workaround is needed.

let neg = -42
let flipped = -x

7. Bit Shifts Take a Plain Integer

The shift amount is a plain integer literal or a variable of any integer type.

let shifted = x >> 4

8. Array Index Requires Cast

Array indices must be usize.

// WRONG
let val = arr[i]
// CORRECT
let val = arr[i as usize]

9. NO Attributes

No #[test], #[derive()], or any other attributes.

10. NO .len() / .push() on Arrays

Fixed arrays are not objects. Track length manually or use stdlib IntVec.

struct IntVec { data: [i64; 4096], len: i64 }
impl IntVec {
    fn push(self: &!IntVec, val: i64) with Mut, Panic {
        self.data[self.len as usize] = val
        self.len = self.len + 1
    }
}

11. Effects Are MANDATORY

Functions with side effects MUST declare them. See .cursor/rules/effects.mdc.

12. Match Arms — NO Commas

match value {
    Pattern1 => result1
    Pattern2 => result2
    _ => default
}