$ cargo eval -- 1 + 1
> 1 + 1
2

$ cargo eval -d fastrand -- 'if fastrand::bool() {
    123 
} else {
    456
}'
> if fastrand::bool() {
    123 
} else {
    456
}
456

$ cargo eval -v -d fastrand -- 'if fastrand::bool() {
    123 
} else {
    456
}'
Cargo.toml
[package]
name = "temp"
version = "0.0.0"
edition = "2021"

[dependencies]
fastrand = "*"

src/main.rs
fn main() -> Result<(), ()> {
    let input = if fastrand::bool() { 123 } else { 456 };
    println!("{}", input);
    Ok(())
}

> if fastrand::bool() {
    123 
} else {
    456
}
123