Macro greenie::iterate_generator

macro_rules! iterate_generator {
    (for ($x: ident in $generator: expr) $b: block) => { ... };
    (for ($x: ident in $generator: expr) $b: block and $b2: block) => { ... };
    (enumerate for ($c: ident, $x: ident in $generator: expr) $b: block) => { ... };
    (enumerate for ($c: ident, $x: ident in $generator: expr) $b: block and $b2: block) => { ... };
}