up

docs/diary/2023-09-17-half-edge.md

@@ -0,0 +1,67 @@
+---
+title: Half edge
+author: Xie Yuheng
+date: 2023-09-17
+---
+
+```
+     \   |   /
+  .-------------.
+  |    \ | /    |
+  |   (.....)   |
+  |      |      |
+  |   (.....)   |
+  |    / | \    |
+  `-------------`
+     /   |   \
+```
+
+> Although during an interaction between two nodes, new nodes and new
+> interactable edges might be introduced, all of the new interactable
+> edges can still be viewed as contained within the circle, during all
+> the new future interactions caused by them, removing and
+> reconnecting will not affect other parts of the graph outside the
+> circle.
+>
+> -- [Programming with interaction nets / section 8](../articles/programming-with-interaction-nets.md#8)
+
+To make implement this, we can not just give each edge an id,
+and make them an entity in the entity store.
+
+Because take the rule between `(zero)` and `(add)` as an example.
+
+```
+     value           value
+       |               |
+     (add)     =>      |
+     /   \              \
+(zero)   addend        addend
+```
+
+After the interaction, the path between `value` and `addend` has two edges.
+
+To reduce this path to one edge again,
+first we might think of deleting edges
+and introduce new edge,
+but we can not to this,
+for nodes outside of the "circle"
+might hold reference to the edges that we want to delete.
+
+One way to handle this (that I can think of),
+is to use `HalfEdge` instead of `Edge`,
+one edge consists of two `HalfEdge`s,
+each `HalfEdge` has an id.
+
+When two edges are connected,
+
+```
+A1|A2 -- B1|B2
+```
+
+we can reduce them to one edge,
+
+```
+A1|B2
+```
+
+without effecting the references to `HalfEdge`s `A1` and `B2`.

src/app/AppReplEventHandler.ts

@@ -42,7 +42,7 @@ export class AppReplEventHandler extends ReplEventHandler {
   loader = new Loader({ fetcher })
 
   greeting(): void {
-    console.log(`iNet ${app.config.packageJson.version}`)
+    console.log(`iNet Cute ${app.config.packageJson.version}`)
   }
 
   async handle(event: ReplEvent): Promise<void> {