Function graph_io_gml::parse_gml

pub fn parse_gml<NodeWeightFn, EdgeWeightFn, N, E>(
    s: &str, 
    node_weight_fn: &NodeWeightFn, 
    edge_weight_fn: &EdgeWeightFn
) -> Result<Graph<N, E, Directed>, &'static str> where
    NodeWeightFn: Fn(Option<&Sexp>) -> Option<N>,
    EdgeWeightFn: Fn(Option<&Sexp>) -> Option<E>,