Hi All,

After seeing the mermaid.js integration in livebook, I had a little idea to create a library on top of :digraph that bridges between a :digraph graph and a mermaid.js flowchart.

Highlights

Inspect

dg = DG.new()
DG.add_vertex(dg, "v1")
DG.add_vertex(dg, "v2", "label 2")
DG.add_vertex(dg, "v3")
DG.add_edge(dg, "v1", "v2")
DG.add_edge(dg, "v1", "v3", "1 to 3")

IO.inspect(dg)

Outputs mermaid.js format flowchart

graph LR
    v1-->v2[label 2]
    v1--1 to 3-->v3

which can be put into livebook mermaid block and will display as

Collectable

Easily add

• vertices [{:vertex, 1}, {:vertex, 2, "label 2"}, ...]
• or edges [{:edge, 1, 2}, {:edge, "a", "b", "label ab"}, ...]

to the graph via Enum.into/2

dg = DG.new()

~w(a b c d e) |> Enum.map(&{:vertex, &1}) |> Enum.into(dg)

~w(a b c d e)
|> Enum.chunk_every(2, 1, :discard)
|> Enum.map(fn [f, t] -> {:edge, f, t} end)
|> Enum.into(dg)

IO.inspect(dg)

outputs

graph LR
    b-->c
    c-->d
    a-->b
    d-->e

Functions

• Most functions from :digraph and :digraph_utils are mirrored under DG.
• Some functions have their parameters re-arranged so that the graph is always the first parameter.
  (namely reachable/2, reachable_neighbours/2, reaching/2 and reaching_neighbours/2)
• new/{0,1,2,3} returns %DG{} instead of an Erlang digraph
• new/2 and new/3 are shortcuts that can add vertices and edges on creation,
  which don’t exist on :digraph

Sigils

~G and ~g are provided so you can copy mermaid.js flowchart and paste into Elixir to get a %DG{}

import DG.Sigil

dg = ~G"""
graph LR
  a[some label]
  b[other label]
  1-->2
  3[three] -- three to four --> 4[four]
  a --> b
"""

caveat: :digraph is stateful (using ets), don’t use the sigil at compile time,
e.g. as a module attribute, it won’t carry over to runtime.
Only use it in runtime code, e.g. function body,
and remember to clean up properly when it’s no longer used, with delete/1.