Representing a graph from a list of edges

A graph can be defined by a list of edges, where an edge is a tuple of vertices. In the Data.Graph package, a vertex is simply Int. In this recipe, we use the buildG function to construct a graph data structure out of a list of edges.

Getting ready

We will be constructing the graph represented in the following diagram:

How to do it...

Create a new file, which we will name Main.hs, and insert the following code:

1. Import the Data.Graph package:

   import Data.Graph

2. Construct a graph using the buildG function from the imported library:

   myGraph :: Graph
   
   myGraph= buildG bounds edges  
     where  bounds = (1,4)
         edges = [ (1,3), (1,4)
                 , (2,3), (2,4) 
                 , (3,4) ]

3. Print out the graph, its edges, and its vertices:

   main = do
     print $ "The edges are " ++ (show.edges) myGraph
     print $ "The vertices are " ++ (show.vertices) myGraph

How it works...

A list of edges is fed to the buildG :: Bounds -> [Edge] -> Graph function to form a graph...