Macro modifier 

macro_rules! modifier {
    ($(<$($name:ident : $bounds:path),+>)? $modifier:ident <$dim:ident>, $trait_name:ident, $doc:expr, $builder_name: ident, $($arg:ident : $ty:ty),*) => { ... };
    ($dim:ident $(<$($name:ident : $bounds:path),+>)? $modifier:ident, $trait_name:ident, $doc:expr, $builder_name:ident, $($arg:ident : $ty:ty),*) => { ... };
}

Creates boilerplate (including a builder extension trait) for modifiers

Example:

modifier!(<F: Fn(&Schedule<Ix1>) -> f64> Magicify<Ix1>,
    MagicifyBuilder,
    r"Apply magic to the schedule",
    magicify,
    magic_amt: usize,
    magic_fn: F
);

impl<F: Fn(&Schedule<Ix1>) -> f64> Modifier<Ix1> for Magicify<F> {
    type Output<T: Generator<Ix1>> = MagicifyGenerator<T, F>;

    fn modify<T: Generator<Ix1>>(self, generator: T) -> Self::Output<T> {
        // ...
    }
}

• The parameter in angle brackets is an optional list generic parameters with bounds
• The second parameter is the name of the modifier. The macro will create a tuple-struct with that name and all the parameters.
• The third supplies documentation to the modifier and to the builder method.
• The fourth is the name of the builder trait that will be automatically implemented on all generators
• The fifth is the name of the builder method that will be able to be called on generators (for example .tm_filter()).
• The rest are arguments to be passed into the modifier’s new function, the builder method, and added as fields to the modifier.