Macro parameter 

macro_rules! parameter {
    ($name:expr) => { ... };
    ($name:expr, $value:expr) => { ... };
    ($name:expr, $($rest:tt)+) => { ... };
    (@parse $p:ident, [fixed = $f:tt, initial = $i:tt]; ) => { ... };
    (@parse $p:ident, [fixed = false, initial = false]; fixed : $value:expr $(, $($rest:tt)*)?) => { ... };
    (@parse $p:ident, [fixed = false, initial = false]; initial : $value:expr $(, $($rest:tt)*)?) => { ... };
    (@parse $p:ident, [fixed = true, initial = false]; initial : $value:expr $(, $($rest:tt)*)?) => { ... };
    (@parse $p:ident, [fixed = false, initial = true]; fixed : $value:expr $(, $($rest:tt)*)?) => { ... };
    (@parse $p:ident, [fixed = $f:tt, initial = $i:tt]; bounds : ($min:expr, $max:expr) $(, $($rest:tt)*)?) => { ... };
    (@parse $p:ident, [fixed = $f:tt, initial = $i:tt]; unit : $value:expr $(, $($rest:tt)*)?) => { ... };
    (@parse $p:ident, [fixed = $f:tt, initial = $i:tt]; latex : $value:expr $(, $($rest:tt)*)?) => { ... };
    (@parse $p:ident, [fixed = $f:tt, initial = $i:tt]; description : $value:expr $(, $($rest:tt)*)?) => { ... };
}

Convenience macro for creating parameters. Usage: parameter!("name") for a free parameter, or parameter!("name", 1.0) for a fixed one.