Switch over to the new ELK driver

Interact between compiler & browser now hooks several nbew places.

3 files changed, 43 insertions, 2 deletions

diff --git a/graph/src/main/java/com/seaofnodes/graph/GraphEvent.java b/graph/src/main/java/com/seaofnodes/graph/GraphEvent.java
new file mode 100644
index 00000000..7d889b21
--- /dev/null
+++ b/graph/src/main/java/com/seaofnodes/graph/GraphEvent.java
@@ -0,0 +1,10 @@
+package com.seaofnodes.graph;
+
+/** IDs refer to nodes in this compilation; near may include nodes since deleted. */
+public record GraphEvent(Kind kind, long peep, long up, String phase,
+                         int node, int repl, int[] near) {
+    public enum Kind { BEFORE, RETURN, APPLY, PHASE }
+
+    public GraphEvent { near = near.clone(); }
+    @Override public int[] near() { return near.clone(); }
+}
diff --git a/graph/src/main/java/com/seaofnodes/graph/GraphJson.java b/graph/src/main/java/com/seaofnodes/graph/GraphJson.java
index 440be034..c27076d3 100644
--- a/graph/src/main/java/com/seaofnodes/graph/GraphJson.java
+++ b/graph/src/main/java/com/seaofnodes/graph/GraphJson.java
@@ -8,10 +8,22 @@ public class GraphJson {
         return sb.toString();
     }
 
-    public static String frame(GraphSnapshot snap, int pos) {
+    public static String frame(GraphSnapshot snap, int pos, GraphEvent evt) {
         var sb = new StringBuilder("{\"snap\":");
         snap(sb, snap);
-        sb.append(",\"pos\":").append(pos);
+        sb.append(",\"pos\":").append(pos).append(",\"evt\":{\"kind\":");
+        str(sb, evt.kind().name());
+        sb.append(",\"peep\":").append(evt.peep()).append(",\"up\":").append(evt.up())
+          .append(",\"phase\":");
+        str(sb, evt.phase());
+        sb.append(",\"node\":").append(evt.node()).append(",\"repl\":").append(evt.repl())
+          .append(",\"near\":[");
+        int[] near = evt.near();
+        for( int i = 0; i < near.length; i++ ) {
+            if( i > 0 ) sb.append(',');
+            sb.append(near[i]);
+        }
+        sb.append("]}");
         return sb.append('}').toString();
     }
 
diff --git a/graph/src/main/java/com/seaofnodes/graph/GraphObserver.java b/graph/src/main/java/com/seaofnodes/graph/GraphObserver.java
new file mode 100644
index 00000000..24879fe2
--- /dev/null
+++ b/graph/src/main/java/com/seaofnodes/graph/GraphObserver.java
@@ -0,0 +1,19 @@
+package com.seaofnodes.graph;
+
+/** Optional, compilation-owned observer. Callbacks read the IR without changing it. */
+public abstract class GraphObserver<N> {
+    public abstract void before(N node);
+
+    /**
+     * repl is null for no progress. applied means substitution and cleanup are
+     * complete; otherwise repl is being returned for the caller to attach.
+     * Calls nest when a rewrite invokes another peephole.
+     */
+    public abstract void after(N node, N repl, boolean applied);
+
+    /** A completed compiler phase. */
+    public abstract void phase(String phase);
+
+    /** A rule consulted a dependency, even if already registered or adjacent. */
+    public void dep(N node, N def) {}
+}