Error Handling

Result

enum Result<T, E> {
    Ok(T),
    Error(E),
}

Result represents recoverable failures that callers must handle explicitly.

? Operator

? propagates an error to the caller if the value is Error.

This is equivalent to early return on Error.

Decisions

• Recoverable errors use Result<T, E>.
• Unrecoverable errors use panic.
• ? is the standard propagation operator for Result.
• ? is not defined for Option<T> in v0.1.

Panic

panic aborts execution when the program is in an invalid state.

Example:

i32 index(i32[] values, i32 i) {
    if i < 0 || i >= values.len() { panic("index out of range"); }
    return values[i];
}

Example:

Result<i32, string> parse_port(string s) {
    let p = int.parse(s)?;
    if p < 1 || p > 65535 {
        return Error("port out of range");
    }
    return Ok(p);
}

Example

Option<i32> maybe_port(string s) {
    // explicit matching; `?` is only for Result in v0.1
    match int.parse(s) {
        Ok(v) => Some(v),
        Error(_) => None,
    }
}

Canonical stdlib API contract for Result is documented in docs/standard-library/Core/Results.md.