pub fn lazy<T, F: FnOnce() -> T>(f: F) -> Node<Lazy<T, F>> {
    Node {
        calc: Lazy(Either::Right(f)),
        graph: None,
    }
}
/// Returns a node whose value is calculated once on demand and cached.
Returns a node whose value is calculated once on demand and cached.
Returns a node whose value is calculated once on demand and cached .
pub fn lazy<T, F: FnOnce() -> T>(f: F) -> Node<Lazy<T, F>> {
    Node {
        calc: Lazy(Either::Right(f)),
        graph: None,
    }
}
pub fn lazy < T , F : FnOnce ( ) -> T > ( f : F ) -> Node < Lazy < T , F > > { Node { calc : Lazy ( Either :: Right ( f ) ) , graph : None , } }
Returns a node whose value is calculated once on demand and cached.
Returns a node whose value is calculated once on demand and cached .
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