"Data.Graph.Builder" is a declarative, monadic language for building graphs, especially trees. It supports both undirected ('UGraphBuilder' and 'buildUGraph') and directed ('DiGraphBuilder', 'buildDiGraph') graphs and allows for optional polymorphic labels on both the vertices and the edges.

The types chosen are designed for easy import from the builder into some other graph library such as FGL or Graphviz.

Here's an example of building a simple, unlabeled, digraph

g = runDiGraphBuilder $ do
  [a, b, c] <- vtcs_ 3
  link_ a b
  d <- vtc_ [b, c]
  link_ d a
  graph_

• Graph unfolds
• Pointed graphs
• Graph gluing