Simple comprehension macro in Rust

comprehension.rs

#[macro_export]
macro_rules! comprehension {
    (($expr:expr) | $id:ident <- ($range:expr) if $cond:expr) => {{
        let mut result = Vec::default();

        for $id in $range {
            if $cond {
                result.push($expr);
            }
        }

        result
    }};
    (($expr:expr) | $id:ident <- ($range:expr)) => {{
        comprehension![ ($expr) | $id <- ($range) if true ]
    }}
}

// Test

#[test]
fn it_apply_comprehension() {
    let result = comprehension![ (x+1) | x <- (1..=2) ];
    assert_eq!(vec![2,3], result);
}

Yes it's really better and much more easier to understand. In addition it corresponds to the comprehension implementation in FP.

Better, I have reversed if construction logic

#[macro_export]
macro_rules! comprehension {
    (($expr:expr) | $id:ident <- ($range:expr) if $cond:expr) => {{
        comprehension![ ($expr) | $id <- ($range.filter(|$id| $cond)) ]
    }};
    (($expr:expr) | $id:ident <- ($range:expr)) => {{
        $range.map(|$id| $expr)
    }}
}

It prevents warning about unused variable when no condition is provided.