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A simple Elixir library for generating GraphViz diagrams.

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elixir-graphviz

Generate GraphViz diagrams from Elixir code.

Restrictions

This module has the following restrictions:

  • Everything has to be properly declared: GraphViz provides a lot of mechanisms for setting up and using default values, but this module doesn't provide access to any of them. This is hopefully less of an issue for a code-generated diagram.

  • Little control over order: dotis notoriously preverse when it comes to ordering nodes or clusters of the same rank. One way to (try to) force this order is to tightly control the order they appear in the file, but this module isn't very friendly in this regard. It basically emits elements in the reverse of the order in which they were added. Arguably dot should finally provide a better way to control this issue, but there seems little chance of that ever hapenning.

  • No validation: GraphViz provides a large but finite set of attributes and values, but this module just allows you to emit anything you want without any regard to whether GraphViz will accept them or not.

  • No formatting: Attributes are expected to be printable (that is, allowed inside \#{...}. There is no automatic " added around attribute values so it is the caller's responsibility to do any form of quoting needed (e.g., if a label contains spaces, the caller needs to use inspect("Foo Bar") as the label instead of simply "Foo Bar". Likewise, if a style should be "round,filled" then the caller needs to use inspect("round,filled") instead of, say, a nice [ :round, :filled ]. The only upside to this is that setting a label to a simple <...html...> "just works". That, and the fact that all attributes are printed exactly the same without any complex special confusing rules. Again, this is hopefully less of an issue for a code-generated diagram.

  • Addition only: You can add elements to the graph but you can't take them out. Mercifully it is at least possible to update elements after they have been added.

  • The node and edge records are defined in a way that caters to directed graphs. Edges therefore have source and target nodes, and nodes have separate incoming and outgoing edge lists.

  • The output isn't formatted in the prettiest or the most compact possible way. On the bright side it is very regular, so you can get away with a simplified parser if you want to post-process it.

Otherwise this is a fairly complete way to generate GraphViz diagrams.

How to use this

First, create a new graph:

graph = GraphViz.Graph[ name: "name", is_strict: true, is_directed: true, attributes: [ label: "A label", rankdir: :LR ] ]

Then, add stuff into the graph:

graph = graph
     |> GraphViz.add(GraphViz.SubGraph[ id: id_of_cluster, is_cluster: true, attributes: [ label: "Cluster" ] ])
     |> GraphViz.add(GraphViz.Node[ id: id_of_source, parent: id_of_cluster, attributes: [ label: "Source" ] ])
     |> GraphViz.add(GraphViz.Node[ id: id_of_target, attributes: [ label: "Target" ] ])
     |> GraphViz.add(GraphViz.Edge[ id: id_of_edge, source: id_of_source, target: id_of_target, attributes: [ label: "Edge" ] ])

You will need to use some sort of a unique identifier for each element (including edges!). Using references (make_ref) is OK, as is using anything else which is unique.

You can lookup existing elements by their identifier:

element = GraphViz.lookup(graph, identifier)

You can give any attribute you want, with any value you want. GraphViz will silently ignore unknown attributes. As long as you keep the identifiers unmolested, you can update an element after creating it:

graph = GraphViz.update(graph, new_version_of_some_element)

Finally, you can print the graph:

GraphViz.print(:stdio, graph)
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