/// Static iteration helper.
#[macro_export] macro_rules! iterate {
    ($expr:expr => $arg: pat => $body:expr) => {
        let mut iter = $expr;
        while let Some(($arg, next)) = iter.next() {
            $body;
            iter = next;
        }
    }
}

/// Implement the const iterator pattern.
#[macro_export] macro_rules! const_iter {
    ($(<$l:lifetime>)?|$self:ident: $Struct:ty| => $Item:ty => $expr:expr) => {
        impl$(<$l>)? Iterator for $Struct {
            type Item = $Item;
            fn next (&mut $self) -> Option<$Item> { $expr }
        }
        impl$(<$l>)? ConstIntoIter for $Struct {
            type Kind = IsIteratorKind;
            type Item = $Item;
            type IntoIter = Self;
        }
    }
}

#[macro_export] macro_rules! get_value {
    ($state:expr => $token:expr) => {
        if let Some(value) = $state.get(&$token.value) {
            value
        } else {
            panic!("no value corresponding to {:?}", &$token.value);
        }
    }
}

#[macro_export] macro_rules! get_content {
    ($state:expr => $token:expr) => {
        if let Some(content) = $state.get_content(&$token.value) {
            content
        } else {
            panic!("no content corresponding to {:?}", &$token.value);
        }
    }
}