2 unstable releases

0.2.0 Sep 3, 2023
0.1.0 Sep 1, 2023

#689 in Procedural macros

MIT license

116 lines


Python-esque for-else construct for Rust


The for-else library introduces a procedural macro, for_!, that extends the capabilities of the standard for loop in Rust. This enhancement allows for an else block to be added directly within the loop, which is executed only if the loop completes without hitting a break statement, closely mirroring Python's for-else construct.


First, add the dependency to your Cargo.toml:

cargo add for-else

Then, use the macros in your code:

use for_else::for_;

// not the best way to test primality, just for demonstration
fn is_prime(n: u32) -> bool {
    if n <= 1 {
        return false;
    for i in 2..n {
        if n % i == 0 {
            return false;

for_! { n in 2100..=2110 {
    if is_prime(n) {
        println!("Found a prime number: {}", n);
} else {
    println!("No prime numbers found in the range.");

In this example, the program searches for the first prime number in the range [2100, 2110]. If a prime is found, it prints the number. If no prime is found, the else block within the for_! macro executes, notifying the user.


For detailed information on each macro and its behavior, please refer to the documentation


Contributions are always welcome! Please open an issue or submit a pull request.




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