Add shared graph viewer to all chapters

18 files changed, 150 insertions, 295 deletions

diff --git a/chapter06/Makefile b/chapter06/Makefile
index cb362b42..8c2d5797 100644
--- a/chapter06/Makefile
+++ b/chapter06/Makefile
@@ -36,6 +36,7 @@ CLZDIR:= build/classes
 main_javas   := $(wildcard $(SRC)/$(SIMPLE)/*java $(SRC)/$(SIMPLE)/*/*java)
 test_javas   := $(wildcard $(TST)/$(SIMPLE)/*java $(TST)/$(SIMPLE)/*/*java)
 main_classes := $(patsubst $(SRC)/%java,$(CLZDIR)/main/%class,$(main_javas))
+include $(firstword $(wildcard ../graph/graph.mk graph/graph.mk))
 test_classes := $(patsubst $(TST)/%java,$(CLZDIR)/test/%class,$(test_javas))
 test_cp      := $(patsubst $(TST)/$(SIMPLE)/%.java,com.seaofnodes.simple.%,$(test_javas))
 classes = $(main_classes) $(test_classes)
@@ -53,7 +54,7 @@ endif
 default: $(default_targets)
 
 # Compile just the out-of-date files
-$(main_classes): build/classes/main/%class: $(SRC)/%java
+$(main_classes): build/classes/main/%class: $(SRC)/%java $(graph_javas)
 	@echo "compiling " $@ " because " $?
 	@[ -d $(CLZDIR)/main ] || mkdir -p $(CLZDIR)/main
 	@javac $(JAVAC_ARGS) -cp "$(CLZDIR)/main$(SEP)$(jars)" -sourcepath $(SRC) -d $(CLZDIR)/main $(main_javas)
@@ -92,4 +93,7 @@ tags:	$(main_javas) $(test_javas)
 	@rm -f TAGS
 	@$(CTAGS) -e --recurse=yes --extra=+q --fields=+fksaiS $(SRC) $(TST)
 
-include ../build-support/chapter-release.mk
+include $(firstword $(wildcard ../build-support/chapter-release.mk build-support/chapter-release.mk))
+
+.PHONY: build
+build: $(main_classes)
diff --git a/chapter06/docs/06-grammar.md b/chapter06/docs/06-grammar.md
index 4cf1cac6..9ed7b160 100644
--- a/chapter06/docs/06-grammar.md
+++ b/chapter06/docs/06-grammar.md
@@ -13,16 +13,12 @@ statement
     | blockStatment
     | expressionStatement
     | ifStatement
-    | metaStatement
     ;
 
 ifStatement
     : 'if' '(' expression ')' statement ('else' statement)?
     ;
 
-metaStatement
-    : '#showGraph' ';'
-    ;
 
 expressionStatement
     : IDENTIFIER '=' expression ';'
diff --git a/chapter06/pom.xml b/chapter06/pom.xml
index fb852b3d..fa76937e 100644
--- a/chapter06/pom.xml
+++ b/chapter06/pom.xml
@@ -11,4 +11,7 @@
     <artifactId>chapter06</artifactId>
     <packaging>jar</packaging>
     <name>Chapter 6</name>
+    <properties>
+        <simple.graph.directory>${project.basedir}/../graph</simple.graph.directory>
+    </properties>
 </project>
diff --git a/chapter06/src/main/java/com/seaofnodes/simple/GraphVisualizer.java b/chapter06/src/main/java/com/seaofnodes/simple/GraphVisualizer.java
deleted file mode 100644
index b30dd450..00000000
--- a/chapter06/src/main/java/com/seaofnodes/simple/GraphVisualizer.java
+++ /dev/null
@@ -1,230 +0,0 @@
-package com.seaofnodes.simple;
-
-import com.seaofnodes.simple.node.*;
-
-import java.util.*;
-
-/**
- * Simple visualizer that outputs GraphViz dot format.
- * The dot output must be saved to a file and run manually via dot to generate the SVG output.
- * Currently, this is done manually.
- */
-public class GraphVisualizer {
-
-    public String generateDotOutput(Parser parser) {
-
-        // Since the graph has cycles, we need to create a flat list of all the
-        // nodes in the graph.
-        Collection<Node> all = findAll(parser);
-        StringBuilder sb = new StringBuilder();
-        sb.append("digraph chapter06 {\n");
-        sb.append("/*\n");
-        sb.append(parser.src());
-        sb.append("\n*/\n");
-
-        // To keep the Scopes below the graph and pointing up into the graph we
-        // need to group the Nodes in a subgraph cluster, and the scopes into a
-        // different subgraph cluster.  THEN we can draw edges between the
-        // scopes and nodes.  If we try to cross subgraph cluster borders while
-        // still making the subgraphs DOT gets confused.
-        sb.append("\trankdir=BT;\n"); // Force Nodes before Scopes
-
-        // Preserve node input order
-        sb.append("\tordering=\"in\";\n");
-
-        // Merge multiple edges hitting the same node.  Makes common shared
-        // nodes much prettier to look at.
-        sb.append("\tconcentrate=\"true\";\n");
-
-        // Just the Nodes first, in a cluster no edges
-        nodes(sb, all);
-
-        // Now the scopes, in a cluster no edges
-        for (ScopeNode sn: parser._xScopes)
-            scopes(sb, sn);
-
-        // Walk the Node edges
-        nodeEdges(sb, all);
-
-        // Walk the Scope edges
-        for (ScopeNode sn: parser._xScopes)
-            scopeEdges(sb, sn);
-
-        sb.append("}\n");
-        return sb.toString();
-    }
-
-
-    private void nodes(StringBuilder sb, Collection<Node> all) {
-        // Just the Nodes first, in a cluster no edges
-        sb.append("\tsubgraph cluster_Nodes {\n"); // Magic "cluster_" in the subgraph name
-        for( Node n : all ) {
-            if( n instanceof ProjNode || n instanceof ScopeNode )
-                continue; // Do not emit, rolled into MultiNode or Scope cluster already
-            sb.append("\t\t").append(n.uniqueName()).append(" [ ");
-            String lab = n.glabel();
-            if( n instanceof MultiNode ) {
-                // Make a box with the MultiNode on top, and all the projections on the bottom
-                sb.append("shape=plaintext label=<\n");
-                sb.append("\t\t\t<TABLE BORDER=\"0\" CELLBORDER=\"1\" CELLSPACING=\"0\" CELLPADDING=\"4\">\n");
-                sb.append("\t\t\t<TR><TD BGCOLOR=\"yellow\">").append(lab).append("</TD></TR>\n");
-                sb.append("\t\t\t<TR>");
-                boolean doProjTable = false;
-                for( Node use : n._outputs ) {
-                    if( use instanceof ProjNode proj ) {
-                        if (!doProjTable) {
-                            doProjTable = true;
-                            sb.append("<TD>").append("\n");
-                            sb.append("\t\t\t\t<TABLE BORDER=\"0\" CELLBORDER=\"1\" CELLSPACING=\"0\">").append("\n");
-                            sb.append("\t\t\t\t<TR>");
-                        }
-                        sb.append("<TD PORT=\"p").append(proj._idx).append("\"");
-                        if( proj.isCFG() ) sb.append(" BGCOLOR=\"yellow\"");
-                        sb.append(">").append(proj.glabel()).append("</TD>");
-                    }
-                }
-                if (doProjTable) {
-                    sb.append("</TR>").append("\n");
-                    sb.append("\t\t\t\t</TABLE>").append("\n");
-                    sb.append("\t\t\t</TD>");
-                }
-                sb.append("</TR>\n");
-                sb.append("\t\t\t</TABLE>>\n\t\t");
-
-            } else {
-                // control nodes have box shape
-                // other nodes are ellipses, i.e. default shape
-                if( n.isCFG() )
-                    sb.append("shape=box style=filled fillcolor=yellow ");
-                if( n instanceof PhiNode )
-                    sb.append("style=filled fillcolor=lightyellow ");
-                sb.append("label=\"").append(lab).append("\" ");
-            }
-            sb.append("];\n");
-        }
-
-        // Force Region & Phis to line up
-        for( Node n : all ) {
-            if( n instanceof RegionNode region ) {
-                sb.append("\t\t{ rank=same; ");
-                sb.append(region).append(";")     ;
-                for( Node phi : region._outputs )
-                    if( phi instanceof PhiNode )
-                        sb.append(phi.uniqueName()).append(";");
-                sb.append("}\n");
-            }
-        }
-
-        sb.append("\t}\n");     // End Node cluster
-    }
-
-    private void scopes( StringBuilder sb, ScopeNode scopenode) {
-        sb.append("\tnode [shape=plaintext];\n");
-        int level=0;
-        for( HashMap<String,Integer> scope : scopenode._scopes ) {
-            String scopeName = makeScopeName(scopenode, level);
-            sb.append("\tsubgraph cluster_").append(scopeName).append(" {\n"); // Magic "cluster_" in the subgraph name
-            sb.append("\t\t").append(scopeName).append(" [label=<\n");
-            sb.append("\t\t\t<TABLE BORDER=\"0\" CELLBORDER=\"1\" CELLSPACING=\"0\">\n");
-            // Add the scope level
-            sb.append("\t\t\t<TR><TD BGCOLOR=\"cyan\">").append(level).append("</TD>");
-            for( String name : scope.keySet() )
-                sb.append("<TD PORT=\"").append(makePortName(scopeName, name)).append("\">").append(name).append("</TD>");
-            sb.append("</TR>\n");
-            sb.append("\t\t\t</TABLE>>];\n");
-            level++;
-        }
-        // Scope clusters nest, so the graphics shows the nested scopes, so
-        // they are not closed as they are printed; so they just keep nesting.
-        // We close them all at once here.
-        sb.append( "\t}\n".repeat( level ) ); // End all Scope clusters
-    }
-
-    private String makeScopeName(ScopeNode sn, int level) { return sn.uniqueName() + "_" + level; }
-    private String makePortName(String scopeName, String varName) { return scopeName + "_" + varName; }
-
-    // Walk the node edges
-    private void nodeEdges(StringBuilder sb, Collection<Node> all) {
-        // All them edge labels
-        sb.append("\tedge [ fontname=Helvetica, fontsize=8 ];\n");
-        for( Node n : all ) {
-            // Do not display the Constant->Start edge;
-            // ProjNodes handled by Multi;
-            // ScopeNodes are done separately
-            if( n instanceof ConstantNode || n instanceof ProjNode || n instanceof ScopeNode )
-                continue;
-            int i=0;
-            for( Node def : n._inputs ) {
-                if( n instanceof PhiNode && def instanceof RegionNode ) {
-                    // Draw a dotted use->def edge from Phi to Region.
-                    sb.append('\t').append(n.uniqueName());
-                    sb.append(" -> ");
-                    sb.append(def.uniqueName());
-                    sb.append(" [style=dotted taillabel=").append(i).append("];\n");
-                } else if( def != null ) {
-                    // Most edges land here use->def
-                    sb.append('\t').append(n.uniqueName()).append(" -> ");
-                    if( def instanceof ProjNode proj ) {
-                        String mname = proj.ctrl().uniqueName();
-                        sb.append(mname).append(":p").append(proj._idx);
-                    } else sb.append(def.uniqueName());
-                    // Number edges, so we can see how they track
-                    sb.append("[taillabel=").append(i);
-                    // control edges are colored red
-                    if( def.isCFG() )
-                        sb.append(" color=red");
-                    sb.append("];\n");
-                }
-                i++;
-            }
-        }
-    }
-
-    // Walk the scope edges
-    private void scopeEdges( StringBuilder sb, ScopeNode scopenode ) {
-        sb.append("\tedge [style=dashed color=cornflowerblue];\n");
-        int level=0;
-        for( HashMap<String,Integer> scope : scopenode._scopes ) {
-            String scopeName = makeScopeName(scopenode, level);
-            for( String name : scope.keySet() ) {
-                Node def = scopenode.in(scope.get(name));
-                if( def==null ) continue;
-                sb.append("\t")
-                  .append(scopeName).append(":")
-                  .append('"').append(makePortName(scopeName, name)).append('"') // wrap port name with quotes because $ctrl is not valid unquoted
-                  .append(" -> ");
-                if( def instanceof ProjNode proj ) {
-                    String mname = proj.ctrl().uniqueName();
-                    sb.append(mname).append(":p").append(proj._idx);
-                } else sb.append(def.uniqueName());
-                sb.append(";\n");
-            }
-            level++;
-        }
-    }
-
-    /**
-     * Finds all nodes in the graph.
-     */
-    private Collection<Node> findAll(Parser parser) {
-        final HashMap<Integer, Node> all = new HashMap<>();
-        for( Node n : Parser.START._outputs )
-            walk(all, n);
-        for( Node n : parser._scope._inputs )
-            walk(all, n);
-        return all.values();
-    }
-
-    /**
-     * Walk a subgraph and populate distinct nodes in the all list.
-     */
-    private void walk(HashMap<Integer,Node> all, Node n) {
-        if(n == null ) return;
-        if (all.get(n._nid) != null) return; // Been there, done that
-        all.put(n._nid, n);
-        for (Node c : n._inputs)
-            walk(all, c);
-        for( Node c : n._outputs )
-            walk(all, c);
-    }
-}
diff --git a/chapter06/src/main/java/com/seaofnodes/simple/Parser.java b/chapter06/src/main/java/com/seaofnodes/simple/Parser.java
index 1a15efa3..9b79c195 100644
--- a/chapter06/src/main/java/com/seaofnodes/simple/Parser.java
+++ b/chapter06/src/main/java/com/seaofnodes/simple/Parser.java
@@ -1,5 +1,7 @@
 package com.seaofnodes.simple;
 
+import com.seaofnodes.graph.GraphObserver;
+
 import com.seaofnodes.simple.node.*;
 import com.seaofnodes.simple.type.*;
 
@@ -14,6 +16,12 @@ import java.util.*;
  */
 public class Parser {
 
+    // Current compilation context; the observer belongs to the parser.
+    public static Parser PARSER;
+    public GraphObserver<Node> _obs;
+    public int pos() { return _lexer._position; }
+
+
     /**
      * A Global Static, unique to each compilation.  This is a public, so we
      * can make constants everywhere without having to thread the StartNode
@@ -62,6 +70,7 @@ public class Parser {
     public final Stack<ScopeNode> _xScopes = new Stack<>();
 
     public Parser(String source, TypeInteger arg) {
+        PARSER = this;
         Node.reset();
         _lexer = new Lexer(source);
         _scope = new ScopeNode();
@@ -85,8 +94,7 @@ public class Parser {
 
     private Node ctrl(Node n) { return _scope.ctrl(n); }
 
-    public StopNode parse() { return parse(false); }
-    public StopNode parse(boolean show) {
+    public StopNode parse() {
         _xScopes.push(_scope);
         // Enter a new scope for the initial control and arguments
         _scope.push();
@@ -97,7 +105,6 @@ public class Parser {
         _xScopes.pop();
         if (!_lexer.isEOF()) throw error("Syntax error, unexpected " + _lexer.getAnyNextToken());
         STOP.peephole();
-        if( show ) showGraph();
         return STOP;
     }
 
@@ -134,7 +141,6 @@ public class Parser {
         else if (matchx("int")) return parseDecl();
         else if (match ("{"  )) return require(parseBlock(),"}");
         else if (matchx("if" )) return parseIf();
-        else if (matchx("#showGraph")) return require(showGraph(),";");
         else if (matchx(";")) return null; // Empty statement
         else return parseExpressionStatement();
     }
@@ -203,14 +209,7 @@ public class Parser {
         return ret;
     }
 
-    /**
-     * Dumps out the node graph
-     * @return {@code null}
-     */
-    private Node showGraph() {
-        System.out.println(new GraphVisualizer().generateDotOutput(this));
-        return null;
-    }
+
 
     /**
      * Parses an expression statement
diff --git a/chapter06/src/main/java/com/seaofnodes/simple/node/AddNode.java b/chapter06/src/main/java/com/seaofnodes/simple/node/AddNode.java
index af2a41b3..1cc20608 100644
--- a/chapter06/src/main/java/com/seaofnodes/simple/node/AddNode.java
+++ b/chapter06/src/main/java/com/seaofnodes/simple/node/AddNode.java
@@ -7,8 +7,6 @@ public class AddNode extends Node {
 
     @Override public String label() { return "Add"; }
 
-    @Override public String glabel() { return "+"; }
-
     @Override
     StringBuilder _print1(StringBuilder sb) {
         in(1)._print0(sb.append("("));
diff --git a/chapter06/src/main/java/com/seaofnodes/simple/node/BoolNode.java b/chapter06/src/main/java/com/seaofnodes/simple/node/BoolNode.java
index 79c65c60..24bca613 100644
--- a/chapter06/src/main/java/com/seaofnodes/simple/node/BoolNode.java
+++ b/chapter06/src/main/java/com/seaofnodes/simple/node/BoolNode.java
@@ -15,9 +15,6 @@ abstract public class BoolNode extends Node {
     public String label() { return getClass().getSimpleName(); }
 
     @Override
-    public String glabel() { return op(); }
-
-    @Override
     StringBuilder _print1(StringBuilder sb) {
         in(1)._print0(sb.append("("));
         in(2)._print0(sb.append(op()));
diff --git a/chapter06/src/main/java/com/seaofnodes/simple/node/DivNode.java b/chapter06/src/main/java/com/seaofnodes/simple/node/DivNode.java
index 519a8c8a..1bb04be7 100644
--- a/chapter06/src/main/java/com/seaofnodes/simple/node/DivNode.java
+++ b/chapter06/src/main/java/com/seaofnodes/simple/node/DivNode.java
@@ -8,8 +8,6 @@ public class DivNode extends Node {
 
     @Override public String label() { return "Div"; }
 
-    @Override public String glabel() { return "//"; }
-
     @Override
     StringBuilder _print1(StringBuilder sb) {
         in(1)._print0(sb.append("("));
diff --git a/chapter06/src/main/java/com/seaofnodes/simple/node/MinusNode.java b/chapter06/src/main/java/com/seaofnodes/simple/node/MinusNode.java
index 0d59ef25..b83c41a5 100644
--- a/chapter06/src/main/java/com/seaofnodes/simple/node/MinusNode.java
+++ b/chapter06/src/main/java/com/seaofnodes/simple/node/MinusNode.java
@@ -8,8 +8,6 @@ public class MinusNode extends Node {
 
     @Override public String label() { return "Minus"; }
 
-    @Override public String glabel() { return "-"; }
-
     @Override
     StringBuilder _print1(StringBuilder sb) {
         in(1)._print0(sb.append("(-"));
diff --git a/chapter06/src/main/java/com/seaofnodes/simple/node/MulNode.java b/chapter06/src/main/java/com/seaofnodes/simple/node/MulNode.java
index 0380c079..20ec7d87 100644
--- a/chapter06/src/main/java/com/seaofnodes/simple/node/MulNode.java
+++ b/chapter06/src/main/java/com/seaofnodes/simple/node/MulNode.java
@@ -8,8 +8,6 @@ public class MulNode extends Node {
 
     @Override public String label() { return "Mul"; }
 
-    @Override public String glabel() { return "*"; }
-
     @Override
     StringBuilder _print1(StringBuilder sb) {
         in(1)._print0(sb.append("("));
diff --git a/chapter06/src/main/java/com/seaofnodes/simple/node/Node.java b/chapter06/src/main/java/com/seaofnodes/simple/node/Node.java
index 44e8dfd2..b533ae34 100644
--- a/chapter06/src/main/java/com/seaofnodes/simple/node/Node.java
+++ b/chapter06/src/main/java/com/seaofnodes/simple/node/Node.java
@@ -1,5 +1,7 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.simple.Parser;
+
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.type.Type;
 
@@ -76,13 +78,9 @@ public abstract class Node {
     // Easy reading label for debugger, e.g. "Add" or "Region" or "EQ"
     public abstract String label();
 
-    // Unique label for graph visualization, e.g. "Add12" or "Region30" or "EQ99"
+    // Unique label for debugging, e.g. "Add12" or "Region30" or "EQ99"
     public String uniqueName() { return label() + _nid; }
 
-    // Graphical label, e.g. "+" or "Region" or "=="
-    public String glabel() { return label(); }
-
-
     // ------------------------------------------------------------------------
 
     // Debugger Printing.
@@ -223,7 +221,7 @@ public abstract class Node {
     }
 
     // Mostly used for asserts and printing.
-    boolean isDead() { return isUnused() && nIns()==0 && _type==null; }
+    public boolean isDead() { return isUnused() && nIns()==0 && _type==null; }
 
     // Shortcuts to stop DCE mid-parse
     // Add bogus null use to keep node alive
@@ -254,12 +252,22 @@ public abstract class Node {
      * code. </li>
      * </ul>
      */
-    public final Node peephole( ) {
+    public final Node peephole() {
+        var obs = Parser.PARSER == null ? null : Parser.PARSER._obs;
+        if( obs != null ) obs.before(this);
+        Type old = _type;
+        Node n = peepholeOpt();
+        Node rez = n == null ? this : n;
+        if( obs != null ) obs.after(this, n == null && old == _type ? null : rez, false);
+        return rez;
+    }
+
+    private Node peepholeOpt() {
         // Compute initial or improved Type
         Type type = _type = compute();
 
         if (_disablePeephole)
-            return this;        // Peephole optimizations turned off
+            return null;        // Peephole optimizations turned off
 
         // Replace constant computations from non-constants with a constant node
         if (!(this instanceof ConstantNode) && type.isConstant())
@@ -273,8 +281,8 @@ public abstract class Node {
             // Recursively optimize
             return deadCodeElim(n.peephole());
 
-        return this;            // No progress
-    }
+        return null;            // No progress
+        }
 
     // m is the new Node, self is the old.
     // Return 'm', which may have zero uses but is alive nonetheless.
diff --git a/chapter06/src/main/java/com/seaofnodes/simple/node/NotNode.java b/chapter06/src/main/java/com/seaofnodes/simple/node/NotNode.java
index e3683646..83c63244 100644
--- a/chapter06/src/main/java/com/seaofnodes/simple/node/NotNode.java
+++ b/chapter06/src/main/java/com/seaofnodes/simple/node/NotNode.java
@@ -8,8 +8,6 @@ public class NotNode extends Node {
 
     @Override public String label() { return "Not"; }
 
-    @Override public String glabel() { return "!"; }
-
     @Override
     StringBuilder _print1(StringBuilder sb) {
         in(1)._print0(sb.append("(!"));
diff --git a/chapter06/src/main/java/com/seaofnodes/simple/node/PhiNode.java b/chapter06/src/main/java/com/seaofnodes/simple/node/PhiNode.java
index 15088e08..f7cf917e 100644
--- a/chapter06/src/main/java/com/seaofnodes/simple/node/PhiNode.java
+++ b/chapter06/src/main/java/com/seaofnodes/simple/node/PhiNode.java
@@ -10,8 +10,6 @@ public class PhiNode extends Node {
 
     @Override public String label() { return "Phi_"+_label; }
 
-    @Override public String glabel() { return "&phi;_"+_label; }
-
     @Override
     StringBuilder _print1(StringBuilder sb) {
         sb.append("Phi(");
diff --git a/chapter06/src/main/java/com/seaofnodes/simple/node/SubNode.java b/chapter06/src/main/java/com/seaofnodes/simple/node/SubNode.java
index 475b3790..2e170273 100644
--- a/chapter06/src/main/java/com/seaofnodes/simple/node/SubNode.java
+++ b/chapter06/src/main/java/com/seaofnodes/simple/node/SubNode.java
@@ -8,8 +8,6 @@ public class SubNode extends Node {
 
     @Override public String label() { return "Sub"; }
 
-    @Override public String glabel() { return "-"; }
-
     @Override
     StringBuilder _print1(StringBuilder sb) {
         in(1)._print0(sb.append("("));
diff --git a/chapter06/src/main/java/com/seaofnodes/simple/print/SimpleGraphAdapter.java b/chapter06/src/main/java/com/seaofnodes/simple/print/SimpleGraphAdapter.java
new file mode 100644
index 00000000..cee75f6a
--- /dev/null
+++ b/chapter06/src/main/java/com/seaofnodes/simple/print/SimpleGraphAdapter.java
@@ -0,0 +1,52 @@
+package com.seaofnodes.simple.print;
+
+import com.seaofnodes.graph.GraphAdapter;
+import com.seaofnodes.graph.GraphSnapshot;
+import com.seaofnodes.graph.GraphSnapshot.*;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.node.Node;
+import java.util.ArrayList;
+
+/** Chapter 6's view of the IR; browser, transport and layout are shared. */
+public class SimpleGraphAdapter extends GraphAdapter<Node> {
+    @Override protected boolean dead(Node n) { return n.isDead(); }
+    @Override protected int id(Node n) { return n._nid; }
+    @Override protected int nIns(Node n) { return n.nIns(); }
+    @Override protected Node in(Node n, int idx) { return n.in(idx); }
+    @Override protected int nOuts(Node n) { return n.nOuts(); }
+    @Override protected Node out(Node n, int idx) { return n.out(idx); }
+
+    private ArrayList<Edge> edges(Node n) {
+        var edges = new ArrayList<Edge>();
+        String[] names = n instanceof ScopeNode scope && n.nIns() != 0 ? scope.reverseNames() : null;
+        for( int i = 0; i < n.nIns(); i++ ) {
+            String name = names == null || i >= names.length ? null : names[i];
+            edges.add(new Edge(i, ref(n.in(i)), role(n, i), name));
+        }
+        return edges;
+    }
+
+    @Override protected GraphSnapshot.Node desc(Node n) {
+        Projection proj = n instanceof ProjNode p ? new Projection(ref(n.in(0)), p._idx) : null;
+        String label = n.label();
+        return new GraphSnapshot.Node(n._nid, label == null ? n.getClass().getSimpleName() : label,
+                                      n._type == null ? null : n._type.toString(), kind(n), edges(n), proj);
+    }
+
+    private Kind kind(Node n) {
+        if( n instanceof ScopeNode ) return Kind.SCOPE;
+        if( n instanceof StartNode ) return Kind.CTRL;
+        if( n instanceof RegionNode ) return Kind.REGION;
+        if( n instanceof PhiNode ) return Kind.PHI;
+        return n.isCFG() ? Kind.CTRL : Kind.DATA;
+    }
+
+    private Role role(Node n, int i) {
+        if( n instanceof ScopeNode || n instanceof ConstantNode ) return Role.ASSOC;
+        if( n instanceof PhiNode ) return i == 0 ? Role.ASSOC : Role.DATA;
+        if( n instanceof ProjNode ) return n.isCFG() ? Role.CTRL : Role.DATA;
+        if( n instanceof RegionNode && i == 0 ) return Role.ASSOC;
+        if( i == 0 || n instanceof RegionNode || n instanceof StopNode ) return Role.CTRL;
+        return Role.DATA;
+    }
+}
diff --git a/chapter06/src/main/java/com/seaofnodes/simple/print/SimpleGraphObserver.java b/chapter06/src/main/java/com/seaofnodes/simple/print/SimpleGraphObserver.java
new file mode 100644
index 00000000..122c7267
--- /dev/null
+++ b/chapter06/src/main/java/com/seaofnodes/simple/print/SimpleGraphObserver.java
@@ -0,0 +1,40 @@
+package com.seaofnodes.simple.print;
+
+import com.seaofnodes.graph.GraphCapture;
+import com.seaofnodes.graph.GraphViewer;
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.node.Node;
+import java.util.ArrayList;
+import java.io.IOException;
+
+/** Chapter 6's compilation context; capture and event bookkeeping are shared. */
+public class SimpleGraphObserver extends GraphCapture<Node> {
+    private Parser _parser;
+    private Node _ret;
+    private String _phase;
+    public SimpleGraphObserver() { super(new SimpleGraphAdapter()); }
+    public static void main(String[] args) throws IOException {
+        GraphViewer.run(new SimpleGraphObserver());
+    }
+    @Override protected void compile(String src) {
+        _parser = new Parser(src);
+        _parser._obs = this;
+        _phase = "Parse";
+        _ret = _parser.parse();
+        phase(_phase);
+    }
+    @Override protected String phase() { return _phase; }
+    @Override protected int pos() { return "Parse".equals(_phase) ? _parser.pos() : -1; }
+    @Override protected void detach() {
+        if( _parser != null ) _parser._obs = null;
+        _parser = null;
+        _ret = null;
+    }
+    @Override protected void roots(ArrayList<Node> roots) {
+        roots.add(Parser.START);
+        roots.add(_parser.STOP);
+        roots.add(_parser._scope);
+        roots.addAll(_parser._xScopes);
+        roots.add(_ret);
+    }
+}
diff --git a/chapter06/src/test/java/com/seaofnodes/simple/Chapter05Test.java b/chapter06/src/test/java/com/seaofnodes/simple/Chapter05Test.java
index 134a8be2..31ca56a0 100644
--- a/chapter06/src/test/java/com/seaofnodes/simple/Chapter05Test.java
+++ b/chapter06/src/test/java/com/seaofnodes/simple/Chapter05Test.java
@@ -19,7 +19,7 @@ else {
     a = arg-3;
 }
 return a;""");
-        StopNode ret = parser.parse(false);
+        StopNode ret = parser.parse();
         assertEquals("return Phi(Region17,(arg+2),(arg-3));", ret.toString());
     }
 
@@ -34,7 +34,7 @@ if (arg == 1) {
     c = 4;
 }
 return c;""", TypeInteger.BOT);
-        StopNode ret = parser.parse(false);
+        StopNode ret = parser.parse();
         assertEquals("return Phi(Region16,4,3);", ret.toString());
     }
 
@@ -62,7 +62,7 @@ if( arg==1 )
 else
     b=a+1;
 return a+b;""");
-        StopNode ret = parser.parse(false);
+        StopNode ret = parser.parse();
         assertEquals("return ((arg*2)+Phi(Region20,2,3));", ret.toString());
     }
 
@@ -77,7 +77,7 @@ if( arg==1 )
 else
     a=b+1;
 return a+b;""");
-        StopNode ret = parser.parse(false);
+        StopNode ret = parser.parse();
         assertEquals("return ((Phi(Region31,(arg*2),arg)+arg)+Phi(Region31,4,5));", ret.toString());
     }
 
@@ -127,7 +127,7 @@ if( arg==1 )
     a=arg==3;
 }
 return a;""");
-        StopNode ret = parser.parse(false);
+        StopNode ret = parser.parse();
         assertEquals("return (arg==Phi(Region16,3,2));", ret.toString());
     }
 
diff --git a/chapter06/src/test/java/com/seaofnodes/simple/Chapter06Test.java b/chapter06/src/test/java/com/seaofnodes/simple/Chapter06Test.java
index 44b49d73..cb58f2bb 100644
--- a/chapter06/src/test/java/com/seaofnodes/simple/Chapter06Test.java
+++ b/chapter06/src/test/java/com/seaofnodes/simple/Chapter06Test.java
@@ -15,7 +15,7 @@ public class Chapter06Test {
 if( true ) return 2;
 return 1;
 """);
-        StopNode stop = parser.parse(false);
+        StopNode stop = parser.parse();
         assertEquals("return 2;", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof ProjNode);
     }
@@ -29,7 +29,7 @@ if (arg)
     a = 2;
 return (arg < a) < 3;
 """);
-        StopNode stop = parser.parse(false);
+        StopNode stop = parser.parse();
         assertEquals("return ((arg<Phi(Region12,2,1))<3);", stop.toString());
     }
 
@@ -44,7 +44,7 @@ else
   a=3;
 return a;
 """);
-        StopNode stop = parser.parse(false);
+        StopNode stop = parser.parse();
         assertEquals("return 2;", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof ProjNode);
     }
@@ -64,7 +64,7 @@ if( a==2 )
 else
     b=5;
 return b;""", TypeInteger.BOT);
-        StopNode stop = parser.parse(false);
+        StopNode stop = parser.parse();
         assertEquals("return Phi(Region32,42,5);", stop.toString());
     }
 
@@ -83,7 +83,7 @@ if( arg==2 )
 else
     b=5;
 return b;""", TypeInteger.BOT);
-        StopNode stop = parser.parse(false);
+        StopNode stop = parser.parse();
         assertEquals("return Phi(Region28,2,5);", stop.toString());
     }
 
@@ -123,7 +123,7 @@ else
     a=5;
 return a;
 """, TypeInteger.constant(1));
-        StopNode stop = parser.parse(false);
+        StopNode stop = parser.parse();
         assertEquals("return 3;", stop.toString());
     }
 
@@ -143,7 +143,7 @@ else
     a=5;
 return a;
 """, TypeInteger.BOT);
-        StopNode stop = parser.parse(false);
+        StopNode stop = parser.parse();
         assertEquals("return Phi(Region36,3,Phi(Region34,4,5));", stop.toString());
     }
 
@@ -163,7 +163,7 @@ else
     a=5;
 return a;
 """, TypeInteger.constant(1));
-        StopNode stop = parser.parse(false);
+        StopNode stop = parser.parse();
         assertEquals("return 3;", stop.toString());
     }
 
@@ -183,7 +183,7 @@ else
     a=5;
 return a;
 """, TypeInteger.constant(3));
-        StopNode stop = parser.parse(false);
+        StopNode stop = parser.parse();
         assertEquals("return 4;", stop.toString());
     }
 
@@ -199,7 +199,7 @@ if( arg ) {
 }
 return a+b;
 """);
-        StopNode ret = parser.parse(false);
+        StopNode ret = parser.parse();
         assertEquals("return Phi(Region22,4,1);", ret.toString());
     }
 
@@ -216,7 +216,7 @@ if( arg ) {
 }
 return a+b;
 """, TypeInteger.constant(1));
-        StopNode ret = parser.parse(false);
+        StopNode ret = parser.parse();
         assertEquals("return 4;", ret.toString());
     }
 
@@ -232,7 +232,7 @@ if( arg ) {
 }
 return a+b;
 """, TypeInteger.constant(0));
-        StopNode ret = parser.parse(false);
+        StopNode ret = parser.parse();
         assertEquals("return 1;", ret.toString());
     }
 
@@ -250,7 +250,7 @@ if( arg ) {
 }
 return a+b+c;
 """);
-        StopNode ret = parser.parse(false);
+        StopNode ret = parser.parse();
         assertEquals("return (Phi(Region33,Phi(Region22,2,3),0)+Phi(Region33,3,1));", ret.toString());
     }
 
@@ -269,7 +269,7 @@ if( arg ) {
 }
 return a+b+c;
 """, TypeInteger.constant(1));
-        StopNode ret = parser.parse(false);
+        StopNode ret = parser.parse();
         assertEquals("return 6;", ret.toString());
     }
 
@@ -287,7 +287,7 @@ if( arg ) {
 }
 return a+b+c;
 """, TypeInteger.constant(2));
-        StopNode ret = parser.parse(false);
+        StopNode ret = parser.parse();
         assertEquals("return 5;", ret.toString());
     }