directed_graph library
Dart implementation of a directed graph. Provides methods to
 add/remove edges,
 check if the graph is acyclic,
 retrieve cycles,
 retrieve a list of vertices in topological order.
Classes

ConstantVertex<
T>  Object representing a constant vertex.

DirectedGraph<
T> 
Generic directed graph.
Data of type
T
is stored in vertices of type Vertex. The graph consists of a mapping_edges
of eachVertex<T>
to a list of connected verticesList<Vertex<T>>
. 
Vertex<
T> 
Generic object representing a vertex in a graph.
Holds data of type
T
.