Directed Acyclic Graphs with TreeView.jl

The TreeView.jl package now has the ability to calculate so-called Directed Acyclic Graphs (DAGs) from a block of Julia code.

This is a higher-level representation of what the code is doing, in which common subexpressions are factored out, using the recently-published CommonSubexpressions.jl package.

An example may be found at the end of this notebook.

Currently the only supported display format is still using TikzGraphs.jl, but Pull Requests are welcome to define plot recipes for the types defined by the package.