Move debug printing into shared space

Same as the graph viewer, moves a lot of code out of all Nodes

43 files changed, 228 insertions, 614 deletions

diff --git a/chapter18/src/main/java/com/seaofnodes/simple/CodeGen.java b/chapter18/src/main/java/com/seaofnodes/simple/CodeGen.java
index a9dfe476..864b3a1a 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/CodeGen.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/CodeGen.java
@@ -129,7 +129,7 @@ public class CodeGen {
 
     // Debugging helper
     @Override public String toString() {
-        return _stop.p(9999);
+        return IRPrinter.prettyPrint(this);
     }
 
     // Debugging helper
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/IRPrinter.java b/chapter18/src/main/java/com/seaofnodes/simple/IRPrinter.java
index bedc7de9..c7ca8cf4 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/IRPrinter.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/IRPrinter.java
@@ -1,301 +1,54 @@
 package com.seaofnodes.simple;
 
+import com.seaofnodes.print.IRAdapter;
 import com.seaofnodes.simple.node.*;
-import com.seaofnodes.simple.type.TypeFunPtr;
 import java.util.ArrayList;
-import java.util.BitSet;
-import java.util.HashMap;
-
-public class IRPrinter {
-
-    // Print a node on 1 line, columnar aligned, as:
-    // NNID NNAME DDEF DDEF  [[  UUSE UUSE  ]]  TYPE
-    // 1234 sssss 1234 1234 1234 1234 1234 1234 tttttt
-    public static SB printLine( Node n, SB sb ) {
-        sb.p("%4d %-7.7s ".formatted(n._nid,n.label()));
-        if( n.isDead() )
-            return sb.p("DEAD\n");
-        for( Node def : n._inputs )
-            sb.p(def==null ? "____" : "%4d".formatted(def._nid))
-                // Lazy Phi indicator
-                .p(n instanceof MemMergeNode && def instanceof MemMergeNode ? "^" : " ");
-        for( int i = n._inputs.size(); i<4; i++ )
-            sb.p("     ");
-        sb.p(" [[  ");
-        for( Node use : n._outputs )
-            sb.p(use==null ? "____ " : "%4d ".formatted(use._nid));
-        int lim = 6 - Math.max(n._inputs.size(),4);
-        for( int i = n._outputs.size(); i<lim; i++ )
-            sb.p("     ");
-        sb.p(" ]]  ");
-        if( n._type!= null ) sb.p(n._type.str());
-        return sb.p("\n");
-    }
-
-
-    public static String prettyPrint(Node node, int depth) {
-        return CodeGen.CODE._phase.ordinal() > CodeGen.Phase.Schedule.ordinal()
-            ? _prettyPrintScheduled( node, depth )
-            : _prettyPrint( node, depth );
-    }
-
-    // Another bulk pretty-printer.  Makes more effort at basic-block grouping.
-    private static String _prettyPrint( Node node, int depth ) {
-        // First, a Breadth First Search at a fixed depth.
-        BFS bfs = new BFS(node,depth);
-        // Convert just that set to a post-order
-        ArrayList<Node> rpos = new ArrayList<>();
-        BitSet visit = new BitSet();
-        for( int i=bfs._lim; i< bfs._bfs.size(); i++ )
-            postOrd( bfs._bfs.get(i), null, rpos, visit, bfs._bs);
-        // Reverse the post-order walk
-        SB sb = new SB();
-        boolean gap=false;
-        for( int i=rpos.size()-1; i>=0; i-- ) {
-            Node n = rpos.get(i);
-            if( n instanceof CFGNode || n.isMultiHead() ) {
-                if( !gap ) sb.p("\n"); // Blank before multihead
-                if( n instanceof FunNode fun ) {
-                    TypeFunPtr sig = fun.sig();
-                    sig.print(sb.p("--- ").p(sig._name==null ? "" : sig._name).p(" "),false).p("----------------------\n");
-                }
-                printLine( n, sb );         // Print head
-                while( --i >= 0 ) {
-                    Node t = rpos.get(i);
-                    if( !t.isMultiTail() ) { i++; break; }
-                    printLine( t, sb );
-                }
-                if( n instanceof ReturnNode ret ) {
-                    TypeFunPtr sig = ret.fun().sig();
-                    sig.print(sb.p("--- ").p(sig._name==null ? "" : sig._name).p(" "),false).p("----------------------\n");
-                }
-                if( !(n instanceof CallNode) ) {
-                    sb.p("\n"); // Blank after multitail
-                    gap = true;
-                }
-            } else {
-                printLine( n, sb );
-                gap = false;
-            }
-        }
-        return sb.toString();
-    }
-
-    private static void postOrd(Node n, Node prior, ArrayList<Node> rpos, BitSet visit, BitSet bfs) {
-        if( !bfs.get(n._nid) )
-            return;  // Not in the BFS visit
-        if( n instanceof FunNode && !(prior instanceof StartNode) )
-            return;                     // Only visit Fun from Start
-        if( visit.get(n._nid) ) return; // Already post-order walked
-        visit.set(n._nid);
-        // First walk the CFG, then everything
-        if( n instanceof CFGNode ) {
-            for( Node use : n._outputs )
-                // Follow CFG, not across call/function borders, and not around backedges
-                if( use instanceof CFGNode && !(n instanceof CallNode && use instanceof FunNode) &&
-                    use.nOuts() >= 1 &&  !(use._outputs.get(0) instanceof LoopNode) )
-                    postOrd(use, n, rpos,visit,bfs);
-            for( Node use : n._outputs )
-                // Follow CFG, not across call/function borders
-                if( use instanceof CFGNode && !(n instanceof CallNode && use instanceof FunNode) )
-                    postOrd(use,n,rpos,visit,bfs);
-        }
-        // Follow all outputs
-        for( Node use : n._outputs )
-            if( use != null &&
-                !(n instanceof CallNode && use instanceof FunNode) &&
-                (n instanceof FunNode || !(use instanceof ParmNode)) )
-                postOrd(use, n, rpos,visit,bfs);
-        // Post-order
-        rpos.add(n);
-    }
-
-    // Breadth-first search, broken out in a class to keep in more independent.
-    // Maintains a root-set of Nodes at the limit (or past by 1 if MultiHead).
-    public static class BFS {
-        // A breadth first search, plus MultiHeads for any MultiTails
-        public final ArrayList<Node> _bfs;
-        public final BitSet _bs; // Visited members by node id
-        public final int _depth; // Depth limit
-        public final int _lim; // From here to _bfs._len can be roots for a reverse search
-        public BFS( Node base, int d ) {
-            _depth = d;
-            _bfs = new ArrayList<>();
-            _bs = new BitSet();
-
-            add(base);                 // Prime the pump
-            int idx=0, lim=1;          // Limit is where depth counter changes
-            while( idx < _bfs.size() ) { // Ran out of nodes below depth
-                Node n = _bfs.get(idx++);
-                for( Node def : n._inputs )
-                    if( def!=null && !_bs.get(def._nid) )
-                        add(def);
-                if( idx==lim ) {    // Depth counter changes at limit
-                    if( --d < 0 )
-                        break;      // Ran out of depth
-                    lim = _bfs.size();  // New depth limit
-                }
-            }
-            // Toss things past the limit except multi-heads
-            while( idx < _bfs.size() ) {
-                Node n = _bfs.get(idx);
-                if( n.isMultiHead() ) idx++;
-                else del(idx);
-            }
-            // Root set is any node with no inputs in the visited set
-            lim = _bfs.size();
-            for( int i=_bfs.size()-1; i>=0; i-- )
-                if( !any_visited(_bfs.get(i)) )
-                    swap( i,--lim);
-            _lim = lim;
-        }
-        void swap( int x, int y ) {
-            if( x==y ) return;
-            Node tx = _bfs.get(x);
-            Node ty = _bfs.get(y);
-            _bfs.set(x,ty);
-            _bfs.set(y,tx);
-        }
-        void add(Node n) {
-            _bfs.add(n);
-            _bs.set(n._nid);
-        }
-        void del(int idx) {
-            _bs.clear(_bfs.get(idx)._nid);
-            Utils.del(_bfs, idx);
-        }
-        boolean any_visited( Node n ) {
-            for( Node def : n._inputs )
-                if( def!=null && _bs.get(def._nid) )
-                    return true;
-            return false;
-        }
-    }
-
-    // Diagnostic block ordering from raw control edges.  Do not call idepth():
-    // it fills compiler caches (and can walk lazy dominator accessors).
-    private static int _idepth(CFGNode cfg, HashMap<Integer,Integer> depths) {
-        if( cfg == null || cfg instanceof StartNode || cfg instanceof FunNode ) return cfg instanceof FunNode ? 1 : 0;
-        Integer old = depths.get(cfg._nid);
-        if( old != null ) return old;
-        depths.put(cfg._nid,0); // Break cycles in partially constructed graphs.
-        int d = 0;
-        if( cfg instanceof LoopNode ) {
-            d = _idepth((CFGNode)cfg.in(1),depths)+1;
-        } else if( cfg instanceof RegionNode || cfg instanceof StopNode ) {
-            for( Node n : cfg._inputs )
-                if( n instanceof CFGNode pred ) d = Math.max(d,_idepth(pred,depths)+1);
-        } else if( cfg.in(0) instanceof CFGNode pred ) {
-            d = _idepth(pred,depths)+1;
-        }
-        depths.put(cfg._nid,d);
-        return d;
+import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.CodeGen;
+
+/** This chapter's read-only IR facts and the familiar debugger entry points. */
+public final class IRPrinter extends IRAdapter<Node> {
+    private static final com.seaofnodes.print.IRPrinter<Node> PRINT =
+        new com.seaofnodes.print.IRPrinter<>(new IRPrinter());
+    @Override public String type(Node n) { return n._type==null ? "" : n._type.str(); }
+    @Override public String inputMark(Node n, Node def) { return n instanceof MemMergeNode && def instanceof MemMergeNode ? "^" : " "; }
+    @Override public Kind kind(Node n) {
+        if( n instanceof StartNode ) return Kind.START;
+        if( n instanceof StopNode ) return Kind.STOP;
+        if( n instanceof FunNode ) return Kind.FUN;
+        if( n instanceof LoopNode ) return Kind.LOOP;
+        if( n instanceof RegionNode ) return Kind.REGION;
+        if( n instanceof ParmNode ) return Kind.PARM;
+        if( n instanceof PhiNode ) return Kind.PHI;
+        if( n instanceof CallEndNode ) return Kind.CALL_END;
+        if( n instanceof CallNode ) return Kind.CALL;
+        if( n instanceof ReturnNode ) return Kind.RETURN;
+        if( n instanceof ConstantNode ) return Kind.CONSTANT;
+        if( n instanceof CProjNode ) return Kind.CPROJ;
+        if( n instanceof ProjNode ) return n instanceof CFGNode ? Kind.CPROJ : Kind.PROJ;
+        if( n instanceof CFGNode ) return Kind.CTRL;
+        if( n instanceof MultiNode ) return Kind.MULTI;
+        return Kind.DATA;
+    }
+    @Override public int index(Node n) {
+        if( n instanceof ProjNode p ) return p._idx;
+        if( n instanceof CProjNode p ) return p._idx;
+        return n._nid;
+    }
+    @Override public String functionName(Node n) { return n.label(); }
+    @Override public String signature(Node n) {
+        FunNode fun=(FunNode)n;
+        return fun.sig().str();
+    }
+
+    public static String prettyPrint(Node n, int depth) { return PRINT.prettyPrint(n,depth); }
+    public static SB printLine(Node n, SB sb) { return sb.p(PRINT.line(n)); }
+
+    public static String prettyPrint(CodeGen code) {
+        var units=new ArrayList<com.seaofnodes.print.IRPrinter.Unit<Node>>();
+        var funs=new ArrayList<Node>();
+        for( Node n : code._start._outputs ) if( n instanceof FunNode ) funs.add(n);
+        units.add(new com.seaofnodes.print.IRPrinter.Unit<>(null,null,null,funs));
+        return PRINT.program(code._start,code._stop,units);
     }
-
-    // Bulk pretty printer, knowing scheduling information is available
-    private static String _prettyPrintScheduled( Node node, int depth ) {
-        // Backwards DFS walk to depth.
-        HashMap<Integer,Integer> ds = new HashMap<>();
-        ArrayList<Node> ns = new ArrayList<>();
-        _walk(ds,ns,node,depth);
-        // Remove data projections, these are force-printed behind their multinode head
-        for( int i=0; i<ns.size(); i++ ) {
-            if( ns.get(i) instanceof ProjNode proj && !(proj.in(0) instanceof CFGNode) ) {
-                Utils.del(ns,i--);
-                ds.remove(proj._nid);
-            }
-        }
-        // Print by block with least diagnostic depth
-        HashMap<Integer,Integer> depths = new HashMap<>();
-        SB sb = new SB();
-        Ary<Node> bns = new Ary<>(Node.class);
-        while( !ds.isEmpty() ) {
-            CFGNode blk = null;
-            for( Node n : ns ) {
-                CFGNode cfg = n instanceof CFGNode cfg0 && cfg0.blockHead() ? cfg0 : n.cfg0();
-                if( blk==null || _idepth(cfg,depths) < _idepth(blk,depths) || (blk instanceof FunNode && !(cfg instanceof FunNode)))
-                    blk = cfg;
-            }
-            Integer d = ds.remove(blk._nid);
-            ns.remove(blk);
-
-            // Print block header
-            sb.p("%-13.13s".formatted(label(blk)+":"));
-            sb.p( "     ".repeat(4) ).p(" [[  ");
-            if( blk instanceof StartNode ) ;
-            else if( blk instanceof RegionNode || blk instanceof StopNode )
-                for( int i=(blk instanceof StopNode ? 3 : 1); i<blk.nIns(); i++ )
-                    label(sb,blk.cfg(i));
-            else
-                label(sb,blk.cfg(0));
-            sb.p(" ]]  \n");
-            printLine(blk,sb);
-
-            // Collect block contents that are in the depth limit
-            bns.clear();
-            int xd = Integer.MAX_VALUE;
-            for( Node use : blk._outputs ) {
-                Integer i = ds.get(use._nid);
-                if( i!=null && !(use instanceof CFGNode cfg && cfg.blockHead()) ) {
-                    if( bns.find(use)==-1 )
-                        bns.add(use);
-                    xd = Math.min(xd,i);
-                }
-            }
-            // Print Phis up front, if any
-            for( int i=0; i<bns.size(); i++ )
-                if( bns.get(i) instanceof PhiNode phi )
-                    printLine( phi, sb,bns,i--,ds,ns);
-
-            // Print block contents in depth order, bumping depth until whole block printed
-            for( ; !bns.isEmpty(); xd++ )
-                for( int i=0; i<bns.size(); i++ ) {
-                    Node n = bns.get(i);
-                    if( ds.get(n._nid)==xd ) {
-                        printLine( n, sb, bns, i--, ds,ns );
-                        if( n instanceof MultiNode && !(n instanceof CFGNode) ) {
-                            for( Node use : n._outputs ) {
-                                printLine(use,sb,bns,bns.indexOf(use),ds,ns);
-                            }
-                        }
-                    }
-                }
-            sb.p("\n");
-        }
-        return sb.toString();
-    }
-
-    private static void _walk( HashMap<Integer,Integer> ds, ArrayList<Node> ns, Node node, int d ) {
-        Integer nd = ds.get(node._nid);
-        if( nd!=null && d <= nd ) return; // Been there, done that
-        Integer old = ds.put(node._nid,d) ;
-        if( old == null )
-          ns.add(node);
-        if( d == 0 ) return;    // Depth cutoff
-        for( Node def : node._inputs )
-            if( def != null &&
-                !(node instanceof LoopNode loop && loop.back()==def) &&
-                // Don't walk into or out of functions
-                !(node instanceof CallEndNode && def instanceof ReturnNode) &&
-                !(node instanceof FunNode && def instanceof CallNode) &&
-                !(node instanceof ParmNode && !(def instanceof FunNode))
-            )
-                _walk(ds,ns,def,d-1);
-    }
-
-    static String label( CFGNode blk ) {
-        if( blk instanceof StartNode ) return "START";
-        return (blk instanceof LoopNode ? "LOOP" : "L")+blk._nid;
-    }
-    static void label( SB sb, CFGNode blk ) {
-        if( !blk.blockHead() ) blk = blk.cfg(0);
-        sb.p( "%-9.9s ".formatted( label( blk ) ) );
-    }
-    static void printLine( Node n, SB sb, Ary<Node> bns, int i, HashMap<Integer,Integer> ds, ArrayList<Node> ns ) {
-        printLine( n, sb );
-        if( i != -1 ) bns.del(i);
-        ds.remove(n._nid);
-        ns.remove(n);
-    }
-
 }
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/AddFNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/AddFNode.java
index 5d0a473a..fd713156 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/AddFNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/AddFNode.java
@@ -1,21 +1,16 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeFloat;
 
-import java.util.BitSet;
 
 public class AddFNode extends Node {
     public AddFNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
 
     @Override public String label() { return "AddF"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        in(1)._print0(sb.append("("), visited);
-        in(2)._print0(sb.append("+"), visited);
-        return sb.append(")");
-    }
+    @Override protected String format() { return "(%1+%2)"; }
 
     @Override
     public Type compute() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/AddNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/AddNode.java
index c3c0254d..08c4d356 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/AddNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/AddNode.java
@@ -1,20 +1,15 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.type.*;
-import java.util.BitSet;
 
 public class AddNode extends Node {
     public AddNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
 
     @Override public String label() { return "Add"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        in(1)._print0(sb.append("("), visited);
-        in(2)._print0(sb.append("+"), visited);
-        return sb.append(")");
-    }
+    @Override protected String format() { return "(%1+%2)"; }
 
 
     @Override
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/BoolNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/BoolNode.java
index 0a885a6a..aa577f61 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/BoolNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/BoolNode.java
@@ -1,10 +1,11 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.type.*;
 
-import java.util.BitSet;
 import static com.seaofnodes.simple.type.TypeInteger.*;
 
 abstract public class BoolNode extends Node {
@@ -18,11 +19,8 @@ abstract public class BoolNode extends Node {
     @Override
     public String label() { return getClass().getSimpleName(); }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        in(1)._print0(sb.append("("), visited);
-        in(2)._print0(sb.append(op()), visited);
-        return sb.append(")");
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        return p.open().n(in(1)).p(op()).n(in(2)).close();
     }
 
     @Override
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/CProjNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/CProjNode.java
index 01119310..70238f8c 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/CProjNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/CProjNode.java
@@ -1,10 +1,11 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeMem;
 import com.seaofnodes.simple.type.TypeTuple;
-import java.util.BitSet;
 
 public class CProjNode extends CFGNode implements MultiUse {
 
@@ -23,7 +24,7 @@ public class CProjNode extends CFGNode implements MultiUse {
     @Override public String label() { return _label; }
     @Override public int idx() { return _idx; }
 
-    @Override StringBuilder _print1(StringBuilder sb, BitSet visited) { return sb.append(_label); }
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) { return p.p(_label); }
 
     @Override public boolean isMultiTail() { return in(0).isMultiHead(); }
     @Override public boolean blockHead() { return true; }
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/CallEndNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/CallEndNode.java
index 54d76bbe..2da09cfc 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/CallEndNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/CallEndNode.java
@@ -1,11 +1,12 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.CodeGen;
 import com.seaofnodes.simple.IterPeeps;
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.type.*;
-import java.util.BitSet;
 
 /**
  *  CallEnd
@@ -26,13 +27,12 @@ public class CallEndNode extends CFGNode implements MultiNode {
     CallNode call() { return (CallNode)in(0); }
 
     @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        sb.append("cend( ");
-        sb.append( in(0) instanceof CallNode ? "Call, " : "----, ");
+    protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        p.p("cend( ");
+        p.p( in(0) instanceof CallNode ? "Call, " : "----, ");
         for( int i=1; i<nIns()-1; i++ )
-            in(i)._print0(sb,visited).append(",");
-        sb.setLength(sb.length()-1);
-        return sb.append(")");
+            p.n(in(i)).p(",");
+        return p.unchar(',').unchar(' ').close();
     }
 
     @Override
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/CallNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/CallNode.java
index 246398ee..442a22e5 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/CallNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/CallNode.java
@@ -1,12 +1,13 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.CodeGen;
 import com.seaofnodes.simple.IterPeeps;
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeFunPtr;
-import java.util.BitSet;
 
 /**
  *  Call
@@ -22,18 +23,17 @@ public class CallNode extends CFGNode {
     public String label() { return "Call"; }
 
     @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+    protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
         String fname = null;
         Node fptr = fptr();
         if( fptr._type instanceof TypeFunPtr tfp && tfp.isConstant() )
             fname = tfp._name;
-        if( fname==null ) fptr._print0(sb,visited);
-        else sb.append(fname);
-        sb.append("( ");
+        if( fname==null ) p.n(fptr);
+        else p.p(fname);
+        p.p("( ");
         for( int i=2; i<nIns()-1; i++ )
-            in(i)._print0(sb,visited).append(",");
-        sb.setLength(sb.length()-1);
-        return sb.append(")");
+            p.n(in(i)).p(",");
+        return p.unchar(',').unchar(' ').close();
     }
 
     Node ctrl() { return in(0); }
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/CastNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/CastNode.java
index 6438abb5..6bf8ee90 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/CastNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/CastNode.java
@@ -1,10 +1,11 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeInteger;
-import java.util.BitSet;
 
 // Upcast (join) the input to a t.  Used after guard test to lift an input.
 // Can also be used to make a type-assertion if ctrl is null.
@@ -18,14 +19,11 @@ public class CastNode extends Node {
 
     @Override public String label() { return "("+_t.str()+")"; }
 
-    @Override
-    public String uniqueName() { return "Cast_" + _nid; }
 
     @Override public boolean isConst() { return true; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        return in(1)._print0(sb.append(label()), visited);
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        return p.p(label()).n(in(1));
     }
 
     @Override
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/ConstantNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/ConstantNode.java
index 83747871..02d0289b 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/ConstantNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/ConstantNode.java
@@ -1,10 +1,11 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.SB;
 import com.seaofnodes.simple.type.Type;
 
-import java.util.BitSet;
 
 /**
  * A Constant node represents a constant value.  At present, the only constants
@@ -31,13 +32,14 @@ public class ConstantNode extends Node {
         return new ConstantNode(type);
     }
 
-    @Override public String  label() { return "#"+_con; }
-    @Override
-    public String uniqueName() { return "Con_" + _nid; }
+    @Override protected String repeatName() {
+        return _con==null || _con.toString().length()<=32 ? null : uniqueName();
+    }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        return sb.append(_con.print(new SB()));
+    @Override public String label() { return "Con"; }
+
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        return p.p(_con.print(new SB()));
     }
 
     @Override public boolean isMultiTail() { return true; }
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/CtrlNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/CtrlNode.java
index 162417bb..9268381a 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/CtrlNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/CtrlNode.java
@@ -1,13 +1,14 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.type.Type;
-import java.util.BitSet;
 
 public class CtrlNode extends CFGNode {
     public CtrlNode() { super(Parser.START); }
     @Override public String label() { return "Ctrl"; }
-    @Override StringBuilder _print1(StringBuilder sb, BitSet visited) { return sb.append("Cctrl"); }
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) { return p.p("Cctrl"); }
     @Override public boolean isConst() { return true; }
     @Override  public Type compute() { return Type.CONTROL; }
     @Override public Node idealize() { return null; }
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/DivFNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/DivFNode.java
index 6c0c2eb3..a3f4318d 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/DivFNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/DivFNode.java
@@ -1,21 +1,16 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeFloat;
 
-import java.util.BitSet;
 
 public class DivFNode extends Node {
     public DivFNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
 
     @Override public String label() { return "DivF"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        in(1)._print0(sb.append("("), visited);
-        in(2)._print0(sb.append("/"), visited);
-        return sb.append(")");
-    }
+    @Override protected String format() { return "(%1/%2)"; }
 
     @Override
     public Type compute() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/DivNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/DivNode.java
index 69b151cd..f0ee21e1 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/DivNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/DivNode.java
@@ -1,20 +1,15 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeInteger;
-import java.util.BitSet;
 
 public class DivNode extends Node {
     public DivNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
 
     @Override public String label() { return "Div"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        in(1)._print0(sb.append("("), visited);
-        in(2)._print0(sb.append("/"), visited);
-        return sb.append(")");
-    }
+    @Override protected String format() { return "(%1/%2)"; }
 
     @Override
     public Type compute() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/FRefNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/FRefNode.java
index f0c4045d..bf1c5a00 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/FRefNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/FRefNode.java
@@ -1,9 +1,10 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.Var;
 import com.seaofnodes.simple.type.Type;
-import java.util.BitSet;
 
 /**
  *  A Forward Reference.  Its any final constant, including functions.  When
@@ -17,10 +18,9 @@ public class FRefNode extends ConstantNode {
 
     @Override public String label() { return "FRef"+_n; }
 
-    @Override public String uniqueName() { return "FRef_" + _nid; }
 
-    @Override StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        return sb.append("FRef_").append(_n);
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        return p.p("FRef_").p(_n);
     }
 
     @Override public Node idealize() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/IfNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/IfNode.java
index c49ee662..a3061b63 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/IfNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/IfNode.java
@@ -1,8 +1,8 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.IterPeeps;
 import com.seaofnodes.simple.type.*;
-import java.util.BitSet;
 import java.util.HashSet;
 
 public class IfNode extends CFGNode implements MultiNode {
@@ -15,11 +15,7 @@ public class IfNode extends CFGNode implements MultiNode {
     @Override
     public String label() { return "If"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        sb.append("if( ");
-        return in(1)._print0(sb, visited).append(" )");
-    }
+    @Override protected String format() { return "if( %1 )"; }
 
     @Override public boolean isMultiHead() { return true; }
 
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/LoadNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/LoadNode.java
index 0ec7c826..0fab82c3 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/LoadNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/LoadNode.java
@@ -1,5 +1,7 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.IterPeeps;
@@ -47,7 +49,7 @@ public class LoadNode extends MemOpNode {
     // Debugger label
     @Override public String  label() { return "ld_"+mlabel(); }
     @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) { return sb.append(".").append(_name); }
+    protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) { return p.p(".").p(_name); }
 
     @Override
     public Type compute() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/LogicalNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/LogicalNode.java
index ccc1f6b5..c59bd948 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/LogicalNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/LogicalNode.java
@@ -1,9 +1,10 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeInteger;
-import java.util.BitSet;
 
 public abstract class LogicalNode extends Node {
     // Source location for late reported errors
@@ -12,11 +13,8 @@ public abstract class LogicalNode extends Node {
     public LogicalNode(Parser.Lexer loc, Node lhs, Node rhs) { super(null, lhs, rhs); _loc = loc; }
     abstract String op();
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        in(1)._print0(sb.append("("), visited);
-        in(2)._print0(sb.append(op()), visited);
-        return sb.append(")");
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        return p.open().n(in(1)).p(op()).n(in(2)).close();
     }
 
 
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java
index 07d703f6..5cb908bb 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java
@@ -1,9 +1,10 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.IterPeeps;
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeMem;
-import java.util.BitSet;
 
 /** A default slice and explicit alias overrides. A null default means partial
  *  memory: absent aliases are not covered, rather than having unknown contents.
@@ -52,14 +53,14 @@ public class MemMergeNode extends Node {
     @Override public String label() { return "MemMerge"; }
     @Override public boolean isMem() { return true; }
     @Override public Type compute() { return TypeMem.BOT; }
-    @Override StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        sb.append("MEM[");
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        p.p("MEM[");
         for( int i=1; i<nIns(); i++ )
             if( in(i)!=null ) {
-                sb.append(i==1 ? "default:" : i+":");
-                in(i)._print0(sb,visited).append(" ");
+                p.p(i==1 ? "default:" : i+":");
+                p.n(in(i)).p(" ");
             }
-        return sb.append("]");
+        return p.p("]");
     }
 
     @Override public Node idealize() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/MinusFNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/MinusFNode.java
index 129963c2..852e646d 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/MinusFNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/MinusFNode.java
@@ -1,20 +1,16 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeFloat;
 
-import java.util.BitSet;
 
 public class MinusFNode extends Node {
     public MinusFNode(Node in) { super(null, in); }
 
     @Override public String label() { return "MinusF"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        in(1)._print0(sb.append("(-"), visited);
-        return sb.append(")");
-    }
+    @Override protected String format() { return "(-%1)"; }
 
     @Override
     public Type compute() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/MinusNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/MinusNode.java
index dad245fd..20220915 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/MinusNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/MinusNode.java
@@ -1,21 +1,17 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeInteger;
 import com.seaofnodes.simple.Utils;
 
-import java.util.BitSet;
 
 public class MinusNode extends Node {
     public MinusNode(Node in) { super(null, in); }
 
     @Override public String label() { return "Minus"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        in(1)._print0(sb.append("(-"), visited);
-        return sb.append(")");
-    }
+    @Override protected String format() { return "(-%1)"; }
 
     @Override
     public Type compute() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/MulFNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/MulFNode.java
index 4b753ba7..6a57f3c5 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/MulFNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/MulFNode.java
@@ -1,21 +1,16 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeFloat;
 
-import java.util.BitSet;
 
 public class MulFNode extends Node {
     public MulFNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
 
     @Override public String label() { return "MulF"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        in(1)._print0(sb.append("("), visited);
-        in(2)._print0(sb.append("*"), visited);
-        return sb.append(")");
-    }
+    @Override protected String format() { return "(%1*%2)"; }
 
     @Override
     public Type compute() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/MulNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/MulNode.java
index 89e35cf2..51dd96cf 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/MulNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/MulNode.java
@@ -1,21 +1,16 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeInteger;
-import java.util.BitSet;
 
 public class MulNode extends Node {
     public MulNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
 
     @Override public String label() { return "Mul"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        in(1)._print0(sb.append("("), visited);
-        in(2)._print0(sb.append("*"), visited);
-        return sb.append(")");
-    }
+    @Override protected String format() { return "(%1*%2)"; }
 
     @Override
     public Type compute() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/NeverNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/NeverNode.java
index e77ed653..7e42ccf9 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/NeverNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/NeverNode.java
@@ -1,11 +1,12 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.type.TypeInteger;
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeTuple;
 
-import java.util.BitSet;
 
 // "Never true" for infinite loop exits
 public class NeverNode extends IfNode {
@@ -13,7 +14,7 @@ public class NeverNode extends IfNode {
 
     @Override public String label() { return "Never"; }
 
-    @Override StringBuilder _print1(StringBuilder sb, BitSet visited) { return sb.append("Never"); }
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) { return p.p("Never"); }
 
     @Override public Type compute() { return TypeTuple.IF_BOTH; }
 
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/NewNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/NewNode.java
index 9f413e7d..cd639d7e 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/NewNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/NewNode.java
@@ -1,7 +1,8 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.type.*;
-import java.util.BitSet;
 
 /** Allocate and initialize an object. Inputs {ctrl, $mem, size, fields...};
  *  results {ptr, $mem}.
@@ -34,10 +35,8 @@ public class NewNode extends Node implements MultiNode {
     @Override public String label() {
         return "new_"+(_ptr._obj.isAry() ? "ary_"+_ptr._obj._fields[1]._type.str() : _ptr._obj.str());
     }
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        sb.append("new ");
-        return sb.append(_ptr._obj.str());
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        return p.p("new ").p(_ptr._obj.str());
     }
 
     // Find matching alias input
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/Node.java b/chapter18/src/main/java/com/seaofnodes/simple/node/Node.java
index cdd218b5..c96255b1 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/Node.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/Node.java
@@ -1,5 +1,7 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.BaseNode;
+
 import com.seaofnodes.simple.CodeGen;
 
 import com.seaofnodes.simple.*;
@@ -13,14 +15,7 @@ import java.util.function.Function;
  * The Node class provides common functionality used by all subtypes.
  * Subtypes of Node specialize by overriding methods.
  */
-public abstract class Node implements Cloneable {
-
-    /**
-     * Each node has a unique dense Node ID within a compilation context
-     * The ID is useful for debugging, for using as an offset in a bitvector,
-     * as well as for computing equality of nodes (to be implemented later).
-     */
-    public int _nid;
+public abstract class Node extends BaseNode<Node> implements Cloneable {
 
     /**
      * Inputs to the node. These are use-def references to Nodes.
@@ -42,14 +37,12 @@ public abstract class Node implements Cloneable {
      */
     public Ary<Node> _outputs;
 
-
     /**
      * Current computed type for this Node.  This value changes as the graph
      * changes and more knowledge is gained about the program.
      */
     public Type _type;
 
-
     /**
      * A private Global Static mutable counter, for unique node id generation.
      * To make the compiler multithreaded, this field will have to move into a TLS.
@@ -59,7 +52,7 @@ public abstract class Node implements Cloneable {
     public static int UID() { return UNIQUE_ID; }
 
     protected Node(Node... inputs) {
-        _nid = UNIQUE_ID++; // allocate unique dense ID
+        super(UNIQUE_ID++); // allocate unique dense ID
         _inputs = new Ary<>(Node.class);
         Collections.addAll(_inputs,inputs);
         _outputs = new Ary<>(Node.class);
@@ -71,41 +64,6 @@ public abstract class Node implements Cloneable {
     // Easy reading label for debugger, e.g. "Add" or "Region" or "EQ"
     public abstract String label();
 
-    // Unique label for debugging, e.g. "Add12" or "Region30" or "EQ99"
-    public String uniqueName() {
-        return label() + _nid;
-    }
-
-    // ------------------------------------------------------------------------
-
-    // Debugger Printing.
-
-    // {@code toString} is what you get in the debugger.  It has to print 1
-    // line (because this is what a debugger typically displays by default) and
-    // has to be robust with broken graph/nodes.
-    @Override
-    public final String toString() {  return print(); }
-
-    // This is a *deep* print.  We print with a mutually recursive tik-tok
-    // style; the common _print0 calls the per-Node _print1, which calls back
-    // to _print0;
-    public final String print() {
-        return _print0(new StringBuilder(), new BitSet()).toString();
-    }
-
-    // This is the common print: check for repeats, check for DEAD and print
-    // "DEAD" else call the per-Node print1.
-    final StringBuilder _print0(StringBuilder sb, BitSet visited) {
-        if (visited.get(_nid) && !(this instanceof ConstantNode) )
-            return sb.append(label());
-        visited.set(_nid);
-        return isDead()
-            ? sb.append(uniqueName()).append(":DEAD")
-            : _print1(sb, visited);
-    }
-    // Every Node implements this; a partial-line recursive print
-    abstract StringBuilder _print1(StringBuilder sb, BitSet visited);
-
     public String p(int depth) { return IRPrinter.prettyPrint(this,depth); }
 
     public boolean isMultiHead() { return false; }
@@ -115,6 +73,8 @@ public abstract class Node implements Cloneable {
     // ------------------------------------------------------------------------
     // Graph Node & Edge manipulation
 
+    @Override public String typeName() { return _type==null ? null : _type.toString(); }
+
     /**
      * Gets the ith input node
      * @param i Offset of the input node
@@ -189,7 +149,6 @@ public abstract class Node implements Cloneable {
         return setDef(idx,new_def);
     }
 
-
     /**
      * Add a new def to an existing Node.  Keep the edges correct by
      * adding the corresponding <em>def->use</em> edge.
@@ -267,7 +226,6 @@ public abstract class Node implements Cloneable {
             kill();
     }
 
-
     // Replace self with nnn in the graph, making 'this' go dead
     public void subsume( Node nnn ) {
         assert nnn!=this;
@@ -449,7 +407,6 @@ public abstract class Node implements Cloneable {
      */
     public abstract Node idealize();
 
-
     // Some of the peephole rules get complex, and search further afield than
     // just the nearest neighbor.  These peepholes can fail the pattern match
     // on a node some distance away, and if that node ever changes we should
@@ -493,7 +450,6 @@ public abstract class Node implements Cloneable {
         _deps.clear();
     }
 
-
     // Global Value Numbering.  Hash over opcode and inputs; hits in this table
     // are structurally equal.
     public static final HashMap<Node,Node> GVN = new HashMap<>();
@@ -515,7 +471,6 @@ public abstract class Node implements Cloneable {
     // and can assume "this!=n" and has the same Java class.
     boolean eq( Node n ) { return true; }
 
-
     // Cached hash.  If zero, then not computed AND this Node is NOT in the GVN
     // table - and can have its edges hacked (which will change his hash
     // anyway).  If Non-Zero then this Node is IN the GVN table, or is being
@@ -531,7 +486,6 @@ public abstract class Node implements Cloneable {
         _hash=0;                // Out of table now
     }
 
-
     // Hash of opcode and inputs
     @Override public final int hashCode() {
         if( _hash != 0 ) return _hash;
@@ -551,7 +505,6 @@ public abstract class Node implements Cloneable {
     /** Is this Node Memory related */
     public boolean isMem() { return false; }
 
-
     // Semantic change to the graph (so NOT a peephole), used by the Parser.
     // If any input is a float, flip to a float-flavored opcode and widen any
     // non-float input.
@@ -572,7 +525,6 @@ public abstract class Node implements Cloneable {
     }
     Node copyF() { return null; }
 
-
     // ------------------------------------------------------------------------
     // Peephole utilities
 
@@ -599,7 +551,6 @@ public abstract class Node implements Cloneable {
         return true;
     }
 
-
     // Make a shallow copy (same class) of this Node, with given inputs and
     // empty outputs and a new Node ID.  The original inputs are ignored.
     // Does not need to be implemented in isCFG() nodes.
@@ -632,7 +583,6 @@ public abstract class Node implements Cloneable {
         ITER_CNT = ITER_NOP_CNT = 0;
     }
 
-
     // Utility to walk the entire graph applying a function; return the first
     // not-null result.
     private static final BitSet WVISIT = new BitSet();
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/NotNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/NotNode.java
index 5e631b78..57fa9301 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/NotNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/NotNode.java
@@ -1,19 +1,15 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.type.*;
-import java.util.BitSet;
 
 public class NotNode extends Node {
     public NotNode(Node in) { super(null, in); }
 
     @Override public String label() { return "Not"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        in(1)._print0(sb.append("(!"), visited);
-        return sb.append(")");
-    }
+    @Override protected String format() { return "(!%1)"; }
 
     @Override
     public TypeInteger compute() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/ParmNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/ParmNode.java
index 78609971..7f5924cc 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/ParmNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/ParmNode.java
@@ -1,8 +1,9 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.type.Type;
-import java.util.BitSet;
 
 public class ParmNode extends PhiNode {
 
@@ -19,18 +20,12 @@ public class ParmNode extends PhiNode {
     public FunNode fun() { return (FunNode)in(0); }
 
     @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+    protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
         if( "main".equals(fun().sig()._name) && _label.equals("arg") )
-            return sb.append("arg");
-        sb.append("Parm_").append(_label).append("(");
-        for( Node in : _inputs ) {
-            if (in == null) sb.append("____");
-            else in._print0(sb, visited);
-            sb.append(",");
-        }
-        sb.setLength(sb.length()-1);
-        sb.append(")");
-        return sb;
+            return p.p("arg");
+        p.p("Parm_").p(_label).open();
+        for( Node in : _inputs ) p.n(in).p(",");
+        return p.unchar(',').close();
     }
 
 
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/PhiNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/PhiNode.java
index 3fdcd6e5..9b5e1c26 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/PhiNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/PhiNode.java
@@ -1,8 +1,9 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.*;
 import com.seaofnodes.simple.type.*;
-import java.util.BitSet;
 
 public class PhiNode extends Node {
 
@@ -29,18 +30,12 @@ public class PhiNode extends Node {
     @Override public String label() { return "Phi_"+MemOpNode.mlabel(_label); }
 
     @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+    protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
         if( !(region() instanceof RegionNode r) || r.inProgress() )
-            sb.append("Z");
-        sb.append("Phi(");
-        for( Node in : _inputs ) {
-            if (in == null) sb.append("____");
-            else in._print0(sb, visited);
-            sb.append(",");
-        }
-        sb.setLength(sb.length()-1);
-        sb.append(")");
-        return sb;
+            p.p("Z");
+        p.p("Phi(");
+        for( Node in : _inputs ) p.n(in).p(",");
+        return p.unchar(',').close();
     }
 
     public CFGNode region() { return (CFGNode)in(0); }
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/ProjNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/ProjNode.java
index 81917bef..1e192676 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/ProjNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/ProjNode.java
@@ -1,10 +1,11 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeMem;
 import com.seaofnodes.simple.type.TypeTuple;
 
-import java.util.BitSet;
 
 public class ProjNode extends Node implements MultiUse {
 
@@ -24,11 +25,11 @@ public class ProjNode extends Node implements MultiUse {
     @Override public int idx() { return _idx; }
 
     @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        if( _label != null )  return sb.append(_label);
+    protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        if( _label != null )  return p.p(_label);
         if( in(0) instanceof CallEndNode cend && cend.call()!=null )
-            return cend.call()._print0(sb,visited);
-        return sb.append("LONELY PROJ");
+            return p.n(cend.call());
+        return p.p("LONELY PROJ");
     }
 
     @Override public CFGNode cfg0() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/ReadOnlyNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/ReadOnlyNode.java
index fddcaa67..fa4e0242 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/ReadOnlyNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/ReadOnlyNode.java
@@ -1,9 +1,9 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeMemPtr;
 
-import java.util.BitSet;
 
 /**
  * Cast a pointer to read-only
@@ -12,10 +12,7 @@ public class ReadOnlyNode extends Node {
     public ReadOnlyNode( Node n ) { super(null,n); }
     @Override public String label() { return "ReadOnly"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        return in(1)._print0(sb.append("(const)"),visited);
-    }
+    @Override protected String format() { return "(const)%1"; }
     @Override public Type compute() {
         Type t = in(1)._type;
         return t instanceof TypeMemPtr tmp ? tmp.makeRO() : t;
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/RegionNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/RegionNode.java
index 157d9109..945398e9 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/RegionNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/RegionNode.java
@@ -1,12 +1,13 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.IterPeeps;
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.type.Type;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.BitSet;
 import java.util.HashSet;
 
 public class RegionNode extends CFGNode {
@@ -19,9 +20,8 @@ public class RegionNode extends CFGNode {
     @Override
     public String label() { return "Region"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        return sb.append(label());
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        return p.p(label());
     }
 
     @Override public boolean isMultiHead() { return true; }
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/ReturnNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/ReturnNode.java
index 9948d973..d4b4094d 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/ReturnNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/ReturnNode.java
@@ -1,10 +1,11 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.SB;
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.type.*;
-import java.util.BitSet;
 
 /** Keeps all preceding memory effects and the return value alive: {ctrl, $mem, value, rpc}. */
 public class ReturnNode extends CFGNode {
@@ -26,10 +27,10 @@ public class ReturnNode extends CFGNode {
     public String label() { return "Return"; }
 
     @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        sb.append("return ");
-        expr()._print0(sb, visited);
-        return sb.append(";");
+    protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        p.p("return ");
+        p.n(expr());
+        return p.p(";");
     }
 
     // No one unique control follows; can be many call end sites
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/RoundF32Node.java b/chapter18/src/main/java/com/seaofnodes/simple/node/RoundF32Node.java
index 3dd7cbf0..78e7698c 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/RoundF32Node.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/RoundF32Node.java
@@ -1,19 +1,16 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeFloat;
 
-import java.util.BitSet;
 
 public class RoundF32Node extends Node {
     public RoundF32Node(Node lhs) { super(null, lhs); }
 
     @Override public String label() { return "RoundF32"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        return in(1)._print0(sb.append("((f32)"), visited).append(")");
-    }
+    @Override protected String format() { return "((f32)%1)"; }
 
     @Override
     public Type compute() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/ScopeNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
index 0b93cee6..5801cdf5 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
@@ -1,5 +1,7 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.*;
 import com.seaofnodes.simple.type.*;
 import java.util.*;
@@ -48,28 +50,26 @@ public class ScopeNode extends Node {
     @Override public String label() { return "Scope"; }
 
     @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        sb.append("Scope[ ");
+    protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        p.p("Scope[ ");
         int j=1;
         for( int i=0; i<nIns(); i++ ) {
-            if( j < _lexSize._len && i == _lexSize.at(j) ) { sb.append("| "); j++; }
+            if( j < _lexSize._len && i == _lexSize.at(j) ) { p.p("| "); j++; }
             Var v = _vars.get(i);
-            sb.append(v._type().print(new SB()));
-            sb.append(" ");
-            if( v._final ) sb.append("!");
-            sb.append(v._name);
-            sb.append("=");
+            p.p(v._type().print(new SB()));
+            p.p(" ");
+            if( v._final ) p.p("!");
+            p.p(v._name);
+            p.p("=");
             Node n = in(i);
             while( n instanceof ScopeNode loop ) {
-                sb.append("Lazy_");
+                p.p("Lazy_");
                 n = loop.in(i);
             }
-            if( n==null ) sb.append("___");
-            else n._print0(sb, visited);
-            sb.append(", ");
+            p.n(n);
+            p.p(", ");
         }
-        sb.setLength(sb.length()-2);
-        return sb.append("]");
+        return p.unchar(", ").p("]");
     }
 
 
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/StartNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/StartNode.java
index e9ab8380..8bdb60cf 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/StartNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/StartNode.java
@@ -1,7 +1,8 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.type.*;
-import java.util.BitSet;
 import java.util.HashSet;
 import static com.seaofnodes.simple.Utils.TODO;
 
@@ -14,9 +15,8 @@ public class StartNode extends LoopNode implements MultiNode {
 
     @Override public String label() { return "Start"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-      return sb.append(label());
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        return p.p(label());
     }
 
     @Override public boolean isMultiHead() { return true; }
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/StopNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/StopNode.java
index cabb7393..a15125a1 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/StopNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/StopNode.java
@@ -1,8 +1,9 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.type.Type;
-import java.util.BitSet;
 
 public class StopNode extends CFGNode {
 
@@ -20,13 +21,13 @@ public class StopNode extends CFGNode {
     }
 
     @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
+    protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
         // For the sake of many old tests, and single value prints as "return val"
-        if( ret()!=null ) return ret()._print0(sb,visited);
-        sb.append("Stop[ ");
+        if( ret()!=null ) return p.n(ret());
+        p.p("Stop[ ");
         for( Node ret : _inputs )
-            ret._print0(sb, visited).append(" ");
-        return sb.append("]");
+            p.n(ret).p(" ");
+        return p.p("]");
     }
 
     @Override public boolean blockHead() { return true; }
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/StoreNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/StoreNode.java
index 92cd2389..ba367a67 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/StoreNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/StoreNode.java
@@ -1,11 +1,12 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.IterPeeps;
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.IterPeeps;
 import com.seaofnodes.simple.type.*;
-import java.util.BitSet;
 
 /**
  * Store represents setting a value to a memory based object, in chapter 10
@@ -38,8 +39,8 @@ public class StoreNode extends MemOpNode {
     public Node val() { return in(4); }
 
     @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        return sb.append(".").append(_name).append("=").append( val()).append(";");
+    protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        return p.p(".").p(_name).p("=").p( val()).p(";");
     }
 
     @Override
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/StructNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/StructNode.java
index 076b342a..b9801f63 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/StructNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/StructNode.java
@@ -1,8 +1,9 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.SB;
 import com.seaofnodes.simple.type.*;
-import java.util.BitSet;
 
 /**
  * Build a compound object
@@ -14,16 +15,15 @@ public class StructNode extends Node {
     @Override public String label() { return _ts==null ? "STRUCT?" : _ts.str(); }
 
     @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        if( _ts==null ) return sb.append("STRUCT?");
-        sb.append(_ts._name).append(" {");
+    protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) {
+        if( _ts==null ) return p.p("STRUCT?");
+        p.p(_ts._name).p(" {");
         for( int i=0; i<nIns(); i++ ) {
-            sb.append(_ts._fields[i]._fname).append(":");
-            sb.append((in(i)==null ? Type.BOTTOM : in(i)._type).print(new SB()));
-            sb.append("; ");
+            p.p(_ts._fields[i]._fname).p(":");
+            p.p((in(i)==null ? Type.BOTTOM : in(i)._type).print(new SB()));
+            p.p("; ");
         }
-        sb.setLength(sb.length()-2);
-        return sb.append("}");
+        return p.unchar("; ").p("}");
     }
 
     @Override
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/SubFNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/SubFNode.java
index 27bbda8d..2d218a03 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/SubFNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/SubFNode.java
@@ -1,21 +1,16 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeFloat;
 
-import java.util.BitSet;
 
 public class SubFNode extends Node {
     public SubFNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
 
     @Override public String label() { return "SubF"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        in(1)._print0(sb.append("("), visited);
-        in(2)._print0(sb.append("-"), visited);
-        return sb.append(")");
-    }
+    @Override protected String format() { return "(%1-%2)"; }
 
     @Override
     public Type compute() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/SubNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/SubNode.java
index 034f2fb1..9bf6d83e 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/SubNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/SubNode.java
@@ -1,21 +1,16 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeInteger;
-import java.util.BitSet;
 
 public class SubNode extends Node {
     public SubNode(Node lhs, Node rhs) { super(null, lhs, rhs); }
 
     @Override public String label() { return "Sub"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        in(1)._print0(sb.append("("), visited);
-        in(2)._print0(sb.append("-"), visited);
-        return sb.append(")");
-    }
+    @Override protected String format() { return "(%1-%2)"; }
 
     @Override
     public Type compute() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/ToFloatNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/ToFloatNode.java
index a4aa8934..7b0122ce 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/ToFloatNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/ToFloatNode.java
@@ -1,20 +1,17 @@
 package com.seaofnodes.simple.node;
 
+
 import com.seaofnodes.simple.type.Type;
 import com.seaofnodes.simple.type.TypeFloat;
 import com.seaofnodes.simple.type.TypeInteger;
 
-import java.util.BitSet;
 
 public class ToFloatNode extends Node {
     public ToFloatNode(Node lhs) { super(null, lhs); }
 
     @Override public String label() { return "ToFloat"; }
 
-    @Override
-    StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        return in(1)._print0(sb.append("(flt)"), visited);
-    }
+    @Override protected String format() { return "(flt)%1"; }
 
     @Override
     public Type compute() {
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/node/XCtrlNode.java b/chapter18/src/main/java/com/seaofnodes/simple/node/XCtrlNode.java
index 3c6a5df3..3eae8548 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/node/XCtrlNode.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/node/XCtrlNode.java
@@ -1,13 +1,14 @@
 package com.seaofnodes.simple.node;
 
+import com.seaofnodes.print.ExprPrinter;
+
 import com.seaofnodes.simple.Parser;
 import com.seaofnodes.simple.type.Type;
-import java.util.BitSet;
 
 public class XCtrlNode extends CFGNode {
     public XCtrlNode() { super(Parser.START); }
     @Override public String label() { return "Xctrl"; }
-    @Override StringBuilder _print1(StringBuilder sb, BitSet visited) { return sb.append("Xctrl"); }
+    @Override protected ExprPrinter<Node> _print1(ExprPrinter<Node> p) { return p.p("Xctrl"); }
     @Override public boolean isConst() { return true; }
     @Override public boolean isMultiTail() { return true; }
     @Override  public Type compute() { return Type.XCONTROL; }
diff --git a/chapter18/src/main/java/com/seaofnodes/simple/print/SimpleGraphAdapter.java b/chapter18/src/main/java/com/seaofnodes/simple/print/SimpleGraphAdapter.java
index bd9fe000..3e23968a 100644
--- a/chapter18/src/main/java/com/seaofnodes/simple/print/SimpleGraphAdapter.java
+++ b/chapter18/src/main/java/com/seaofnodes/simple/print/SimpleGraphAdapter.java
@@ -1,45 +1,25 @@
 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 com.seaofnodes.simple.type.TypeMem;
-import java.util.ArrayList;
 
 /** Chapter 18'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); }
-    @Override protected int nDeps(Node n) { return n.nDeps(); }
-    @Override protected Node dep(Node n, int idx) { return n.dep(idx); }
 
-    private ArrayList<Edge> edges(Node n) {
-        var edges = new ArrayList<Edge>();
-        for( int i = 0; i < n.nIns(); i++ ) {
-            String name = n instanceof ScopeNode scope && i < scope._vars.size()
+    @Override protected String edgeName(Node n, int i) {
+        return n instanceof ScopeNode scope && i < scope._vars.size()
                 ? scope._vars.get(i)._name : null;
-            int jump = n instanceof CallEndNode && i>0 && n.in(i) instanceof ReturnNode ret
-                ? ref(ret.fun()) : 0;
-            edges.add(new Edge(i, ref(n.in(i)), role(n, i), name, jump));
-        }
-        return edges;
     }
-
-    @Override protected GraphSnapshot.Node desc(Node n) {
-        Projection proj = n instanceof ProjNode p ? new Projection(ref(n.in(0)), p._idx)
-            : n instanceof CProjNode 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, folding(n));
+    @Override protected int edgeJump(Node n, int i) {
+        return n instanceof CallEndNode && i>0 && n.in(i) instanceof ReturnNode ret
+                ? ref(ret.fun()) : 0;
     }
+    @Override protected int projectionIndex(Node n) { return n instanceof ProjNode p ? p._idx : n instanceof CProjNode p ? p._idx : -1; }
 
-    private boolean folding(Node n) {
+    @Override protected boolean folding(Node n) {
         if( n instanceof FunNode fun ) return fun.folding();
         if( n instanceof ReturnNode ret ) return ret.fun().folding();
         if( n instanceof CallEndNode cend ) return cend.folding();
@@ -49,7 +29,7 @@ public class SimpleGraphAdapter extends GraphAdapter<Node> {
         return false;
     }
 
-    private Kind kind(Node n) {
+    @Override protected Kind kind(Node n) {
         if( n instanceof StopNode ) return Kind.STOP;
         if( n instanceof ScopeNode ) return Kind.SCOPE;
         if( n instanceof FunNode ) return Kind.FUN;
@@ -60,7 +40,7 @@ public class SimpleGraphAdapter extends GraphAdapter<Node> {
         return n instanceof CFGNode ? Kind.CTRL : isMem(n) ? Kind.MEM : Kind.DATA;
     }
 
-    private Role role(Node n, int i) {
+    @Override protected Role role(Node n, int i) {
         if( n instanceof ScopeNode || n instanceof ConstantNode || n instanceof CtrlNode || n instanceof XCtrlNode ) return Role.ASSOC;
         if( n instanceof PhiNode ) return i == 0 ? Role.ASSOC : isMem(n) ? Role.MEM : Role.DATA;
         if( n instanceof ProjNode || n instanceof CProjNode )