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author | William Carroll <wpcarro@gmail.com> | 2019-10-09T11·13+0100 |
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committer | William Carroll <wpcarro@gmail.com> | 2019-12-24T15·21+0000 |
commit | 6b456c1b7a4f6899f063a6e65355af51901d9c7a (patch) | |
tree | cfc70d74818ae9fabdbbfb0cf16cce092e4c1a09 /configs/shared/.emacs.d/wpc/graph.el | |
parent | a7c72adb2ebec1e497fc040eaf3551d564d61a5b (diff) |
Massive configuration overhaul
Currently paying the price of months of non-diligent git usage. Here's what has changed. - Theming support in Gvcci and wpgtk - Dropping support for i3 - Supporting EXWM - Many Elisp modules - Collapsed redundant directories in ./configs
Diffstat (limited to 'configs/shared/.emacs.d/wpc/graph.el')
-rw-r--r-- | configs/shared/.emacs.d/wpc/graph.el | 91 |
1 files changed, 91 insertions, 0 deletions
diff --git a/configs/shared/.emacs.d/wpc/graph.el b/configs/shared/.emacs.d/wpc/graph.el new file mode 100644 index 000000000000..c68c308590f4 --- /dev/null +++ b/configs/shared/.emacs.d/wpc/graph.el @@ -0,0 +1,91 @@ +;;; graph.el --- Working with in-memory graphs -*- lexical-binding: t -*- +;; Author: William Carroll <wpcarro@gmail.com> + +;;; Commentary: +;; +;; Remember that there are optimal three ways to model a graph: +;; 1. Edge List +;; 2. Vertex Table (a.k.a. Neighbors Table) +;; 3. Adjacency Matrix +;; +;; I may call these "Edges", "Neighbors", "Adjacencies" to avoid verbose naming. +;; For now, I'm avoiding dealing with Adjacency Matrices as I don't have an +;; immediate use-case for them. This is subject to change. +;; +;; There are also hybrid representations of graphs that combine the three +;; aforementioned models. I believe Erlang's digraph module models graphs in +;; Erlang Term Storage (i.e. ETS) this way. +;; TODO: Verify this claim. +;; +;; Graphs can be weighted or unweighted. They can also be directed or +;; undirected. +;; TODO: Create a table explaining all graph variants. +;; +;; TODO: Figure out the relationship of this module and tree.el, which should in +;; principle overlap. + +;;; Code: + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; Dependencies +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +(require 'prelude) + +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; +;; Library +;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; + +;; For now, I'll support storing *either* neighbors or edges in the graph struct +;; as long as both aren't set, since that introduces consistency issues. I may +;; want to handle that use-case in the future, but not now. +(cl-defstruct graph neighbors edges) + +;; TODO: How do you find the starting point for a topo sort? +(defun graph/sort (xs) + "Return a topological sort of XS.") + +(defun graph/from-edges (xs) + "Create a graph struct from the Edge List, XS. +The user must pass in a valid Edge List since asserting on the shape of XS might + be expensive." + (make-graph :edges xs)) + +(defun graph/from-neighbors (xs) + "Create a graph struct from a Neighbors Table, XS. +The user must pass in a valid Neighbors Table since asserting on the shape of + XS might be expensive." + (make-graph :neighbors xs)) + +(defun graph/instance? (xs) + "Return t if XS is a graph struct." + (graph-p xs)) + +;; TODO: Model each of the mapping functions into an isomorphism. +(defun graph/edges->neighbors (xs) + "Map Edge List, XS, into a Neighbors Table." + (prelude/assert (graph/instance? xs))) + +(defun graph/neighbors->edges (xs) + "Map Neighbors Table, XS, into an Edge List." + (prelude/assert (graph/instance? xs))) + +;; Below are three different models of the same unweighted, directed graph. + +(defvar graph/edges + '((a . b) (a . c) (a . e) + (b . c) (b . d) + (c . e) + (d . f) + (e . d) (e . f))) + +(defvar graph/neighbors + ((a b c e) + (b c d) + (c e) + (d f) + (e d g) + (f))) + +(provide 'graph) +;;; graph.el ends here |