Chapter 17a: Mutability and Read-Only Views

Co-authored-by: Jun Kawasaki <jun784@gmail.com>

23 files changed, 373 insertions, 310 deletions

diff --git a/src/test/java/com/seaofnodes/simple/BrainFuckTest.java b/src/test/java/com/seaofnodes/simple/BrainFuckTest.java
deleted file mode 100644
index 29ef8732..00000000
--- a/src/test/java/com/seaofnodes/simple/BrainFuckTest.java
+++ /dev/null
@@ -1,80 +0,0 @@
-package com.seaofnodes.simple;
-
-import com.seaofnodes.simple.evaluator.Evaluator;
-import com.seaofnodes.simple.node.StopNode;
-import org.junit.Test;
-import org.junit.Ignore;
-
-import java.nio.charset.StandardCharsets;
-
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.fail;
-
-public class BrainFuckTest {
-
-    @Test
-    public void testBrainfuck() {
-        var program = "++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.".getBytes(StandardCharsets.UTF_8);
-        var encoded = new StringBuilder("u8[] program = new u8[").append(program.length).append("];");
-        for (int i = 0; i < program.length; i++) {
-            int value = program[i] & 0xFF;
-            encoded.append("program[").append(i).append("] = ").append(value).append(";");
-        }
-
-        Parser parser = new Parser(
-                encoded + """
-int pc = 0;
-int d = 0;
-u8[] data = new u8[100];
-u8[] output = new u8[0];
-
-while (pc < program#) {
-    int command = program[pc];
-    if (command == 62) {
-        d = d + 1;
-    } else if (command == 60) {
-        d = d - 1;
-    } else if (command == 43) {
-        data[d] = data[d] + 1;
-    } else if (command == 45) {
-        data[d] = data[d] - 1;
-    } else if (command == 46) {
-        u8[] old = output;
-        output = new u8[output# + 1];
-        int i = 0;
-        while (i < old#) {
-            output[i] = old[i];
-            i = i + 1;
-        }
-        output[i] = data[d];
-    } else if (command == 44) {
-        data[d] = 42;
-    } else if (command == 91) {
-        if (data[d] == 0) {
-            int d = 1;
-            while (d > 0) {
-                pc = pc + 1;
-                command = program[pc];
-                if (command == 91) d = d + 1;
-                if (command == 93) d = d - 1;
-            }
-        }
-    } else if (command == 93) {
-        if (data[d] != 0) {
-            int d = 1;
-            while (d > 0) {
-                pc = pc - 1;
-                command = program[pc];
-                if (command == 93) d = d + 1;
-                if (command == 91) d = d - 1;
-            }
-        }
-    }
-    pc = pc + 1;
-}
-return output;
-                """);
-        StopNode stop = parser.parse().iterate();
-        assertEquals("Hello World!\n", Evaluator.evaluate(stop, 0, 10000).toString());
-    }
-}
diff --git a/src/test/java/com/seaofnodes/simple/Chapter01Test.java b/src/test/java/com/seaofnodes/simple/Chapter01Test.java
index c10dc510..f7524c17 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter01Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter01Test.java
@@ -58,7 +58,7 @@ public class Chapter01Test {
     @Test
     public void testNotBad3() {
         // this test used to fail in chapter 1
-        assertEquals("return 12;", new Parser("return --12;").parse().print());
+        assertEquals("return 12;", new Parser("return - -12;").parse().print());
     }
 
     @Test
diff --git a/src/test/java/com/seaofnodes/simple/Chapter03Test.java b/src/test/java/com/seaofnodes/simple/Chapter03Test.java
index 609dff76..f06e5dcf 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter03Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter03Test.java
@@ -59,7 +59,7 @@ public class Chapter03Test {
     @Test
     public void testBad1() {
         try {
-            new Parser("int a=1; int b=2; int c=0; { int b=3; c=a+b;").parse();
+            new Parser("int a=1; int b=2; int !c=0; { int b=3; c=a+b;").parse();
             fail();
         } catch( RuntimeException e ) {
             assertEquals("Syntax error, expected }: ",e.getMessage());
diff --git a/src/test/java/com/seaofnodes/simple/Chapter04Test.java b/src/test/java/com/seaofnodes/simple/Chapter04Test.java
index 14d31245..36727a8f 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter04Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter04Test.java
@@ -127,14 +127,14 @@ public class Chapter04Test {
 
     @Test
     public void testBug1() {
-        Parser parser = new Parser("int a=arg+1; int b=a; b=1; return a+2; ");
+        Parser parser = new Parser("int a=arg+1; int !b=a; b=1; return a+2; ");
         StopNode ret = parser.parse();
         assertEquals("return (arg+3);", ret.print());
     }
 
     @Test
     public void testBug2() {
-        Parser parser = new Parser("int a=arg+1; a=a; return a; ");
+        Parser parser = new Parser("int !a=arg+1; a=a; return a; ");
         StopNode ret = parser.parse();
         assertEquals("return (arg+1);", ret.print());
     }
diff --git a/src/test/java/com/seaofnodes/simple/Chapter05Test.java b/src/test/java/com/seaofnodes/simple/Chapter05Test.java
index cd646126..7ea75f49 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter05Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter05Test.java
@@ -17,12 +17,11 @@ if (arg == 1)
     a = arg+2;
 else {
     a = arg-3;
-
 }
-
-return a;""");
+return a;
+""");
         StopNode ret = parser.parse().iterate();
-        assertEquals("return Phi(Region21,(arg+2),(arg-3));", ret.toString());
+        assertEquals("return Phi(Region,(arg+2),(arg-3));", ret.toString());
     }
 
     @Test
@@ -37,7 +36,7 @@ if (arg == 1) {
 }
 return c;""", TypeInteger.BOT);
         StopNode ret = parser.parse().iterate();
-        assertEquals("return Phi(Region20,4,3);", ret.toString());
+        assertEquals("return Phi(Region,4,3);", ret.toString());
     }
 
     @Test
@@ -65,7 +64,7 @@ else
     b=a+1;
 return a+b;""");
         StopNode ret = parser.parse().iterate();
-        assertEquals("return ((arg*2)+Phi(Region24,2,3));", ret.toString());
+        assertEquals("return ((arg*2)+Phi(Region,2,3));", ret.toString());
     }
 
     @Test
@@ -80,7 +79,7 @@ else
     a=b+1;
 return a+b;""");
         StopNode ret = parser.parse().iterate();
-        assertEquals("return ((Phi(Region35,(arg*2),arg)+arg)+Phi(Region,4,5));", ret.toString());
+        assertEquals("return ((Phi(Region,(arg*2),arg)+arg)+Phi(Region,4,5));", ret.toString());
     }
 
     @Test
@@ -100,7 +99,7 @@ else
 return a;
 """, TypeInteger.BOT);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Region39,Phi(Region25,2,3),Phi(Region37,4,5));", stop.toString());
+        assertEquals("return Phi(Region,Phi(Region,2,3),Phi(Region,4,5));", stop.toString());
     }
 
     @Test
@@ -116,7 +115,7 @@ if( arg==0 )
 return arg+a+b;
 """, TypeInteger.BOT);
         StopNode stop = parser.parse();
-        assertEquals("return ((arg+Phi(Region18,1,0))+Phi(Region34,2,0));", stop.toString());
+        assertEquals("return ((arg+Phi(Region,1,0))+Phi(Region,2,0));", stop.toString());
     }
 
     @Test
@@ -130,7 +129,7 @@ if( arg==1 )
 }
 return a;""");
         StopNode ret = parser.parse().iterate();
-        assertEquals("return (arg==Phi(Region20,3,2));", ret.toString());
+        assertEquals("return (arg==Phi(Region,3,2));", ret.toString());
     }
 
     @Test
diff --git a/src/test/java/com/seaofnodes/simple/Chapter06Test.java b/src/test/java/com/seaofnodes/simple/Chapter06Test.java
index d2c46df5..50c0580d 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter06Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter06Test.java
@@ -65,7 +65,7 @@ else
     b=5;
 return b;""", TypeInteger.BOT);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Region40,42,5);", stop.toString());
+        assertEquals("return Phi(Region,42,5);", stop.toString());
     }
 
     @Test
@@ -84,7 +84,7 @@ else
     b=5;
 return b;""", TypeInteger.BOT);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Region33,2,5);", stop.toString());
+        assertEquals("return Phi(Region,2,5);", stop.toString());
     }
 
     @Test
@@ -144,7 +144,7 @@ else
 return a;
 """, TypeInteger.BOT);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Region44,3,Phi(Region42,4,5));", stop.toString());
+        assertEquals("return Phi(Region,3,Phi(Region,4,5));", stop.toString());
     }
 
     @Test
@@ -200,7 +200,7 @@ if( arg ) {
 return a+b;
 """);
         StopNode ret = parser.parse().iterate();
-        assertEquals("return Phi(Region29,4,1);", ret.toString());
+        assertEquals("return Phi(Region,4,1);", ret.toString());
     }
 
 
@@ -251,7 +251,7 @@ if( arg ) {
 return a+b+c;
 """);
         StopNode ret = parser.parse().iterate();
-        assertEquals("return (Phi(Region41,Phi(Region26,2,3),0)+Phi(Region,3,1));", ret.toString());
+        assertEquals("return (Phi(Region,Phi(Region,2,3),0)+Phi(Region,3,1));", ret.toString());
     }
 
 
diff --git a/src/test/java/com/seaofnodes/simple/Chapter07Test.java b/src/test/java/com/seaofnodes/simple/Chapter07Test.java
index 443b0d17..ad3622c9 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter07Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter07Test.java
@@ -10,14 +10,14 @@ public class Chapter07Test {
     @Test
     public void testExample() {
         Parser parser = new Parser(
-                """
-                while(arg < 10) {
-                    arg = arg + 1;
-                }
-                return arg;
-                """);
+"""
+while(arg < 10) {
+    arg = arg + 1;
+}
+return arg;
+""");
         StopNode stop = parser.parse();
-        assertEquals("return Phi(Loop9,arg,(Phi_arg+1));", stop.toString());
+        assertEquals("return Phi(Loop,arg,(Phi_arg+1));", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
@@ -34,7 +34,7 @@ if(arg){}else{
 return a;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Region27,1,Phi(Loop16,1,(Phi_a+1)));", stop.toString());
+        assertEquals("return Phi(Region,1,Phi(Loop,1,(Phi_a+1)));", stop.toString());
     }
 
     @Test
@@ -54,7 +54,7 @@ while(i < arg) {
 return sum;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop11,0,Phi(Loop23,Phi_sum,(Phi_sum+Phi(Loop,0,(Phi_j+1)))));", stop.toString());
+        assertEquals("return Phi(Loop,0,Phi(Loop,Phi_sum,(Phi_sum+Phi(Loop,0,(Phi_j+1)))));", stop.toString());
     }
 
     @Test
@@ -70,7 +70,7 @@ while(a < 10) {
 return b;
 """);
         StopNode stop = parser.parse();
-        assertEquals("return Phi(Loop11,2,Phi(Region30,Phi_b,4));", stop.toString());
+        assertEquals("return Phi(Loop,2,Phi(Region,Phi_b,4));", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
@@ -89,7 +89,7 @@ while(a < 10) {
 return b;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop11,2,(Phi(Region30,Phi_b,4)+1));", stop.toString());
+        assertEquals("return Phi(Loop,2,(Phi(Region,Phi_b,4)+1));", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
@@ -106,7 +106,7 @@ while(a < 10) {
 return a;
 """);
         StopNode stop = parser.parse();
-        assertEquals("return Phi(Loop10,1,(Phi_a+3));", stop.toString());
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
@@ -122,7 +122,7 @@ while(a < 10) {
 return a;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop10,1,(Phi_a+3));", stop.toString());
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
@@ -135,7 +135,7 @@ while(arg) a = 2;
 return a;
 """);
         StopNode stop = parser.parse();
-        assertEquals("return Phi(Loop10,1,2);", stop.toString());
+        assertEquals("return Phi(Loop,1,2);", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
@@ -148,7 +148,7 @@ while(arg) a = 2;
 return a;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop10,1,2);", stop.toString());
+        assertEquals("return Phi(Loop,1,2);", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
@@ -164,7 +164,7 @@ while(a < 10) {
 return a;
 """);
         StopNode stop = parser.parse();
-        assertEquals("return Phi(Loop10,1,(Phi_a+3));", stop.toString());
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
@@ -180,7 +180,7 @@ while(a < 10) {
 return a;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop10,1,(Phi_a+3));", stop.toString());
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
@@ -197,7 +197,7 @@ while(a < 10) {
 return a;
 """);
         StopNode stop = parser.parse();
-        assertEquals("return Phi(Loop11,1,(Phi_a+3));", stop.toString());
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
@@ -214,7 +214,7 @@ while(a < 10) {
 return a;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop11,1,(Phi_a+3));", stop.toString());
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
diff --git a/src/test/java/com/seaofnodes/simple/Chapter08Test.java b/src/test/java/com/seaofnodes/simple/Chapter08Test.java
index 89ce8313..bb3bd674 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter08Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter08Test.java
@@ -23,7 +23,7 @@ while(arg < 10) {
 return arg;
                 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Region38,Phi(Region27,Phi(Loop9,arg,(Phi_arg+1)),Add),Add);", stop.toString());
+        assertEquals("return Phi(Region,Phi(Region,Phi(Loop,arg,(Phi_arg+1)),Add),Add);", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof RegionNode);
         Assert.assertEquals(5L, Evaluator.evaluate(stop, 1));
         Assert.assertEquals(10L, Evaluator.evaluate(stop, 6));
@@ -46,7 +46,7 @@ while(arg < 10) {
 return a;
                 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop10,1,Phi(Region44,Phi_a,(Phi_a+1)));", stop.toString());
+        assertEquals("return Phi(Loop,1,Phi(Region,Phi_a,(Phi_a+1)));", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
@@ -65,7 +65,7 @@ while(arg < 10) {
 return arg;
                 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Region36,Phi(Loop9,arg,(Phi_arg+1)),Add);", stop.toString());
+        assertEquals("return Phi(Region,Phi(Loop,arg,(Phi_arg+1)),Add);", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof RegionNode);
     }
 
@@ -81,7 +81,7 @@ while(arg < 10) {
 return arg;
                 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Region27,Phi(Loop9,arg,(Phi_arg+1)),Add);", stop.toString());
+        assertEquals("return Phi(Region,Phi(Loop,arg,(Phi_arg+1)),Add);", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof RegionNode);
     }
 
@@ -100,7 +100,7 @@ while(arg < 10) {
 return arg;
                 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop9,arg,(Phi_arg+1));", stop.toString());
+        assertEquals("return Phi(Loop,arg,(Phi_arg+1));", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
@@ -117,7 +117,7 @@ while(arg < 10) {
 return arg;
                 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop9,arg,(Phi_arg+1));", stop.toString());
+        assertEquals("return Phi(Loop,arg,(Phi_arg+1));", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode);
     }
 
@@ -138,7 +138,7 @@ return arg;
 
     @Test
     public void testRegress2() {
-        Parser parser = new Parser("if(1) return 0;  else while(arg>--arg) arg=arg+1; return 0;");
+        Parser parser = new Parser("if(1) return 0;  else while(arg>- -arg) arg=arg+1; return 0;");
         StopNode stop = parser.parse().iterate();
         assertEquals("return 0;", stop.toString());
     }
@@ -185,7 +185,7 @@ while(arg < 10) {
 return a;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Region30,Phi(Loop10,1,(Phi_a+1)),Add);", stop.toString());
+        assertEquals("return Phi(Region,Phi(Loop,1,(Phi_a+1)),Add);", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof RegionNode);
     }
 
@@ -201,7 +201,7 @@ while(1) {
 return a;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return (Phi(Loop10,1,Add)+1);", stop.toString());
+        assertEquals("return (Phi(Loop,1,Add)+1);", stop.toString());
         assertTrue(stop.ret().ctrl() instanceof CProjNode prj && prj._idx==1 );
     }
 
diff --git a/src/test/java/com/seaofnodes/simple/Chapter09Test.java b/src/test/java/com/seaofnodes/simple/Chapter09Test.java
index 49ee75a2..c31afcd6 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter09Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter09Test.java
@@ -69,7 +69,7 @@ while (arg < 10) {
 return arg;
                 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop10,arg,(Phi_arg+2));", stop.toString());
+        assertEquals("return Phi(Loop,arg,(Phi_arg+2));", stop.toString());
         Assert.assertEquals(11L, Evaluator.evaluate(stop, 1));
     }
 
@@ -86,7 +86,7 @@ while (arg < 10) {
 return arg;
                 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop11,arg,(Phi_arg+4));", stop.toString());
+        assertEquals("return Phi(Loop,arg,(Phi_arg+4));", stop.toString());
         Assert.assertEquals(13L, Evaluator.evaluate(stop, 1));
     }
 
@@ -115,7 +115,7 @@ while (arg) {
 return arg;
                 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop17,arg,(Phi_arg+1));", stop.toString());
+        assertEquals("return 0;", stop.toString());
     }
 
     @Test
@@ -185,7 +185,7 @@ while(arg) {
 return a;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop12,0,(-(Phi_a+3)));", stop.toString());
+        assertEquals("return Phi(Loop,0,(-(Phi_a+3)));", stop.toString());
     }
 
     @Test
@@ -283,7 +283,7 @@ return v1+v0;
     public void testFuzz8() {
         Parser parser = new Parser("while(arg) arg = arg - 1;  return arg;");
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop9,arg,(Phi_arg-1));", stop.toString());
+        assertEquals("return 0;", stop.toString());
     }
 
     @Test
diff --git a/src/test/java/com/seaofnodes/simple/Chapter10Test.java b/src/test/java/com/seaofnodes/simple/Chapter10Test.java
index 0b8be64b..f634e421 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter10Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter10Test.java
@@ -25,7 +25,7 @@ public class Chapter10Test {
     // Issue #246: null-check guards start in Chapter 10; arrays arrive in Chapter 15.
     private static final String NULLABLE_POINT_SOURCE = """
         struct Point { int x; };
-        Point?[] points = new Point?[2];
+        !Point?[] !points = new !Point?[2];
         points[arg] = new Point { x = 42; };
         Point? p = points[1];
         """;
@@ -101,7 +101,7 @@ struct Foo {
     int x;
 };
 Foo? foo = null;
-Bar bar = new Bar;
+!Bar !bar = new Bar;
 bar.a = 1;
 bar.a = 2;
 return bar.a;
@@ -114,7 +114,7 @@ return bar.a;
     public void testExample() {
         Parser parser = new Parser("""
 struct Vector2D { int x; int y; };
-Vector2D v = new Vector2D;
+!Vector2D !v = new Vector2D;
 v.x = 1;
 if (arg)
     v.y = 2;
@@ -153,7 +153,7 @@ arg=0+new s0.0;
     public void testLoop() {
         Parser parser = new Parser("""
 struct Bar { int a; };
-Bar bar = new Bar;
+!Bar !bar = new Bar;
 while (arg) {
     bar.a = bar.a + 2;
     arg = arg + 1;
@@ -161,14 +161,14 @@ while (arg) {
 return bar.a;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop17,0,(Phi_a+2));", stop.toString());
+        assertEquals("return Phi(Loop,0,(Phi_a+2));", stop.toString());
     }
 
     @Test
     public void testIf() {
         Parser parser = new Parser("""
 struct Bar { int a; };
-Bar bar = new Bar;
+!Bar !bar = new Bar;
 if (arg) bar = null;
 bar.a = 1;
 return bar.a;
@@ -181,7 +181,7 @@ return bar.a;
     public void testIf2() {
         Parser parser = new Parser("""
 struct Bar { int a; };
-Bar? bar = null;
+!Bar? !bar = null;
 if (arg) bar = new Bar;
 bar.a = 1;
 return bar.a;
@@ -207,13 +207,13 @@ return bar.a;
     public void testIfOrNull() {
         Parser parser = new Parser("""
 struct Bar { int a; };
-Bar? bar = new Bar;
+!Bar? !bar = new Bar;
 if (arg) bar = null;
 if( bar ) bar.a = 1;
 return bar;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Region38,(*void)Phi(Region24,null,Bar),null);", stop.toString());
+        assertEquals("return Phi(Region,(*void)Phi(Region,null,Bar),null);", stop.toString());
     }
 
     @Test
@@ -221,7 +221,7 @@ return bar;
         Parser parser = new Parser(
 """
 struct Bar { int a; };
-Bar? bar = new Bar;
+!Bar? !bar = new Bar;
 if (arg) bar = null;
 int rez = 3;
 if( !bar ) rez=4;
@@ -229,14 +229,14 @@ else bar.a = 1;
 return rez;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Region44,4,3);", stop.toString());
+        assertEquals("return Phi(Region,4,3);", stop.toString());
     }
 
     @Test
     public void testWhileWithNullInside() {
         Parser parser = new Parser("""
 struct s0 {int v0;};
-s0? v0 = new s0;
+!s0? !v0 = new s0;
 int ret = 0;
 while(arg) {
     ret = v0.v0;
@@ -257,7 +257,7 @@ struct s0 {
     int v0;
 };
 s0? v1=new s0;
-s0? v1;
+!s0? !v1;
 v1=new s0;
 """);
         try { parser.parse(); fail(); }
@@ -273,7 +273,7 @@ struct Iter {
     int x;
     int len;
 };
-Iter i = new Iter;
+!Iter !i = new Iter;
 i.len = arg;
 int sum=0;
 while( i.x < i.len ) {
@@ -283,7 +283,7 @@ while( i.x < i.len ) {
 return sum;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop22,0,(Phi(Loop,0,(Phi_x+1))+Phi_sum));", stop.toString());
+        assertEquals("return Phi(Loop,0,(Phi(Loop,0,(Phi_x+1))+Phi_sum));", stop.toString());
     }
 
 
@@ -291,9 +291,9 @@ return sum;
     public void test1() {
         Parser parser = new Parser("""
 struct s0 {int v0;};
-s0 ret = new s0;
+!s0 !ret = new s0;
 while(arg) {
-    s0 v0 = new s0;
+    !s0 !v0 = new s0;
     v0.v0 = arg;
     arg = arg-1;
     if (arg==5) ret=v0;
@@ -302,15 +302,15 @@ while(arg) {
 return ret;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop17,s0,Phi(Region44,s0,Phi_ret));", stop.toString());
+        assertEquals("return Phi(Loop,s0,Phi(Region,s0,Phi_ret));", stop.toString());
     }
 
     @Test
     public void test2() {
         Parser parser = new Parser("""
 struct s0 {int v0;};
-s0 ret = new s0;
-s0 v0 = new s0;
+!s0 !ret = new s0;
+!s0 !v0 = new s0;
 while(arg) {
     v0.v0 = arg;
     arg = arg-1;
@@ -320,7 +320,7 @@ while(arg) {
 return ret;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop23,s0,Phi(Region45,s0,Phi_ret));", stop.toString());
+        assertEquals("return Phi(Loop,s0,Phi(Region,s0,Phi_ret));", stop.toString());
     }
 
 
@@ -328,16 +328,16 @@ return ret;
     public void test3() {
         Parser parser = new Parser("""
 struct s0 {int v0;};
-s0 ret = new s0;
+!s0 !ret = new s0;
 while(arg < 10) {
-    s0 v0 = new s0;
+    !s0 !v0 = new s0;
     if (arg == 5) ret=v0;
     arg = arg + 1;
 }
 return ret;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop17,s0,Phi(Region41,s0,Phi_ret));", stop.toString());
+        assertEquals("return Phi(Loop,s0,Phi(Region,s0,Phi_ret));", stop.toString());
     }
 
     @Test
@@ -407,7 +407,7 @@ s0 v1 = v0;
 return v1;
     """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return s0;", stop.toString());
+        assertEquals("return (const)s0;", stop.toString());
     }
 
 
@@ -456,9 +456,9 @@ return 0;
     @Test public void testReadBeforeStores() {
         var stop = new Parser("""
             struct S { int x; int y; };
-            S a = new S; S b = new S;
+            !S !a = new S; !S !b = new S;
             a.x = 11; b.x = 22;
-            S p = a; if (arg) p = b;
+            !S !p = a; if (arg) p = b;
             int before = p.x;
             a.y = 55; b.y = 66;
             a.x = 33; b.x = 44;
@@ -470,7 +470,7 @@ return 0;
 
     static final String NESTED_MEMORY = """
             struct S { int x; int y; int z; };
-            S s = new S;
+            !S !s = new S;
             s.x = 5; s.y = 7; s.z = 11;
             while (arg > 0) {
                 s.x = s.x + 1;
@@ -501,7 +501,7 @@ return 0;
     @Test public void testMemoryAtEarlyReturns() {
         var stop = new Parser("""
             struct S { int x; int y; int z; };
-            S s = new S;
+            !S !s = new S;
             s.x = 3; s.y = 5; s.z = 7;
             if (arg) { s.x = 11; s.z = 13; return s; }
             s.y = 17;
@@ -517,9 +517,9 @@ return 0;
     @Test public void testKeepLoadsAtMerge() {
         StopNode stop = new Parser("""
             struct S { int x; };
-            S a = new S; S b = new S;
+            !S !a = new S; !S !b = new S;
             a.x = arg; b.x = arg+1;
-            S p = a; S q = b;
+            !S !p = a; !S !q = b;
             if (arg<0) { p=b; q=a; }
             int v;
             if (arg>1) v=p.x; else v=q.x;
@@ -535,7 +535,7 @@ return 0;
     @Test public void testDropStores() {
         StopNode stop = new Parser("""
             struct S { int x; };
-            S s = new S;
+            !S !s = new S;
             if (arg) s.x=arg+1; else s.x=arg+2;
             return s;
             """).parse().iterate();
@@ -547,9 +547,9 @@ return 0;
     @Test public void testKeepReadsBeforeWrites() {
         StopNode stop = new Parser("""
             struct S { int x; int y; };
-            S a = new S; S b = new S;
+            !S !a = new S; !S !b = new S;
             a.x=arg; b.x=arg+1;
-            S p=a; S q=b;
+            !S !p=a; !S !q=b;
             if (arg<0) { p=b; q=a; }
             int v;
             if (arg>1) { v=p.x; p.x=41; p.y=5; }
diff --git a/src/test/java/com/seaofnodes/simple/Chapter11Test.java b/src/test/java/com/seaofnodes/simple/Chapter11Test.java
index e009c6b6..60ff05d8 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter11Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter11Test.java
@@ -9,7 +9,7 @@ public class Chapter11Test {
     @Test public void testIndependentField() {
         var stop = new Parser("""
             struct S { int x; int y; };
-            S s = new S;
+            !S !s = new S;
             s.x = 42;
             while (arg > 0) { s.y = s.y + arg; arg = arg - 1; }
             return s.x;
@@ -22,8 +22,8 @@ public class Chapter11Test {
     @Test public void testParallelMemoryPhis() {
         var stop = new Parser("""
             struct S { int x; int y; int z; };
-            S a = new S; S b = new S;
-            S p = a; if (arg) p = b;
+            !S !a = new S; !S !b = new S;
+            !S !p = a; if (arg) p = b;
             while (arg > 0) {
                 a.x = p.x + arg;
                 a.y = p.y + 2;
diff --git a/src/test/java/com/seaofnodes/simple/Chapter12Test.java b/src/test/java/com/seaofnodes/simple/Chapter12Test.java
index 4e34028b5..628f6211 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter12Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter12Test.java
@@ -24,10 +24,10 @@ return 3.14;
     public void testLinkedList0() {
         Parser parser = new Parser(
 """
-struct LLI { LLI? next; int i; };
-LLI? head = null;
+struct LLI { !LLI? !next; int i; };
+!LLI? !head = null;
 while( arg ) {
-    LLI x = new LLI;
+    !LLI !x = new LLI;
     x.next = head;
     x.i = arg;
     head = x;
@@ -43,10 +43,10 @@ return head.next.i;
     public void testLinkedList1() {
         Parser parser = new Parser(
 """
-struct LLI { LLI? next; int i; };
-LLI? head = null;
+struct LLI { !LLI? !next; int i; };
+!LLI? !head = null;
 while( arg ) {
-    LLI x = new LLI;
+    !LLI !x = new LLI;
     x.next = head;
     x.i = arg;
     head = x;
@@ -66,11 +66,11 @@ return next.i;
     public void testCoRecur() {
         Parser parser = new Parser(
 """
-struct int0 { int i; flt0? f; };
-struct flt0 { flt f; int0? i; };
-int0 i0 = new int0;
+struct int0 { int i; !flt0? !f; };
+struct flt0 { flt f; !int0? !i; };
+!int0 !i0 = new int0;
 i0.i = 17;
-flt0 f0 = new flt0;
+!flt0 !f0 = new flt0;
 f0.f = 3.14;
 i0.f = f0;
 f0.i = i0;
@@ -84,7 +84,7 @@ return f0.i.f.i.i;
     public void testNullRef0() {
         Parser parser = new Parser(
 """
-struct N { N? next; int i; };
+struct N { !N? !next; int i; };
 N n = new N;
 return n.next;
 """);
@@ -97,12 +97,12 @@ return n.next;
         Parser parser = new Parser(
 """
 struct M { int m; };
-struct N { M next; int i; };
+struct N { !M !next; int i; };
 N n = new N { next = new M; };
 return n.next;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return M;", stop.toString());
+        assertEquals("return (const)M;", stop.toString());
     }
 
     @Test
@@ -110,7 +110,7 @@ return n.next;
         Parser parser = new Parser(
 """
 struct M { int m; };
-struct N { M next; int i; };
+struct N { !M !next; int i; };
 N n = new N { next = null; }
 return n.next;
 """);
@@ -122,8 +122,8 @@ return n.next;
     public void testNullRef3() {
         Parser parser = new Parser(
 """
-struct N { N? next; int i; };
-N n = new N;
+struct N { !N? !next; int i; };
+!N !n = new N;
 n.i = 3.14;
 return n.i;
 """);
@@ -132,9 +132,9 @@ return n.i;
 
     @Test
     public void testNullRef4() {
-        Parser parser = new Parser("-null-5/null-5");
+        Parser parser = new Parser("-null-5/null-5;");
         try { parser.parse().iterate(); fail(); }
-        catch( Exception e ) { assertEquals("Expected an identifier, found 'null'",e.getMessage()); }
+        catch( Exception e ) { assertEquals("Cannot 'Add' null",e.getMessage()); }
     }
 
     @Test public void testNullRef5() {
@@ -158,7 +158,7 @@ struct S{};
     public void testForwardRef0() {
         Parser parser = new Parser(
 """
-struct S1 { S2 s; };
+struct S1 { !S2? !s; };
 return new S2;
 """);
         try { parser.parse().iterate(); fail(); }
@@ -169,7 +169,7 @@ return new S2;
     public void testForwardRef1() {
         Parser parser = new Parser(
 """
-struct S1 { S2? s; };
+struct S1 { !S2? !s; };
 struct S2 { int x; };
 return new S1.s=new S2;
 """);
@@ -182,9 +182,9 @@ return new S1.s=new S2;
         Parser parser = new Parser(
 """
 struct I {int i;};
-struct P { I? pi; };
-P p1 = new P;
-P p2 = new P;
+struct P { !I? !pi; };
+!P !p1 = new P;
+!P !p2 = new P;
 p2.pi = new I;
 p2.pi.i = 2;
 if (arg) p1 = new P;
diff --git a/src/test/java/com/seaofnodes/simple/Chapter13Test.java b/src/test/java/com/seaofnodes/simple/Chapter13Test.java
index c749aba6..695777e2 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter13Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter13Test.java
@@ -15,7 +15,7 @@ public class Chapter13Test {
     public void testFuzzer() {
         Parser parser = new Parser(
 """
-while(-----arg) {
+while(---- -arg) {
     while(-arg) {
         while(-----arg*---0) {
                 int N=--false==false<--arg;
@@ -104,7 +104,7 @@ while(-----arg) {
             int UX=arg;
             while(UX<-3*arg) {
                 UX=UX+arg/-1;
-                arg=-3--(-UX--47<arg==--arg==arg)/arg--UX>=-arg;
+                arg=-3--(-UX- -47<arg==--arg==arg)/arg- -UX>=-arg;
                 if(---12) while(-UX) break;
                 break;
             }
@@ -225,9 +225,9 @@ if(arg!=62==arg) {
                 }
             }
             arg=-arg+arg;
-            arg=--47+-arg<1>arg*(-arg==-arg--0>3);
+            arg=--47+-arg<1>arg*(-arg==-arg- -0>3);
             arg=(----arg)!=arg+--59;
-            arg=--4+arg==-(arg)-arg;
+            arg=- -4+arg==-(arg)-arg;
         }
         else {
             while(--true-----true*-25+-18>arg>=-----(-arg)---13) {
@@ -325,7 +325,7 @@ while( prime <= arg ) {
 return primeCount;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("Stop[ return 0; return Phi(Loop21,1,Phi(Region88,Phi_primeCount,Phi(Region82,(Phi_primeCount+1),Phi_primeCount))); ]", stop.toString());
+        assertEquals("Stop[ return 0; return Phi(Loop,1,Phi(Region,Phi_primeCount,Phi(Region,(Phi_primeCount+1),Phi_primeCount))); ]", stop.toString());
         assertEquals(0L, Evaluator.evaluate(stop,  1)); // No primes 1 or below
         assertEquals(1L, Evaluator.evaluate(stop,  2)); // 2
         assertEquals(2L, Evaluator.evaluate(stop,  3)); // 2, 3
@@ -339,7 +339,7 @@ return primeCount;
         Parser parser = new Parser(
 """
 struct S { int f; };
-S v=new S;
+!S !v=new S;
 v.f = 2;
 int i=new S.f;
 i=v.f;
@@ -357,9 +357,9 @@ return i;
         Parser parser = new Parser(
 """
 struct S { int f; };
-S v = new S;
+!S !v = new S;
 v.f = arg;
-S t = new S;
+!S !t = new S;
 int i = 0;
 if (arg) {
     if (arg+1) v = t;
@@ -370,7 +370,7 @@ if (arg) {
 return i;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Region48,.f,0);", stop.toString());
+        assertEquals("return Phi(Region,.f,0);", stop.toString());
     }
 
     @Test
@@ -378,8 +378,8 @@ return i;
         Parser parser = new Parser(
 """
 struct S { int f; };
-S v0 = new S;
-S? v1;
+!S !v0 = new S;
+!S? !v1;
 if (arg) v1 = new S;
 if (v1) {
     v0.f = v1.f;
@@ -398,7 +398,7 @@ return v0;
         Parser parser = new Parser(
 """
 struct S { int f; };
-S v = new S;
+!S !v = new S;
 v.f = arg;
 S t = new S;
 int i = v.f;
@@ -415,7 +415,7 @@ return i;
         Parser parser = new Parser(
 """
 struct S { int f; };
-S v = new S;
+!S !v = new S;
 while(1) {
     while(arg+1) { arg=arg-1; }
     if (arg) break;
@@ -432,14 +432,14 @@ return v;
         Parser parser = new Parser(
 """
 struct s { int v; };
-s ptr=new s;
+!s !ptr=new s;
 while( -arg )
   ptr = new s;
 while(1)
   arg = arg+ptr.v;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("Stop[ return 0; return 0; ]", stop.toString());
+        assertEquals("return 0;", stop.toString());
     }
 
     @Test
@@ -447,7 +447,7 @@ while(1)
         Parser parser = new Parser(
 """
 struct S { int f; };
-S v = new S;
+!S !v = new S;
 S t = new S;
 int i = v.f;
 while (arg) {
@@ -465,7 +465,7 @@ return i;
         Parser parser = new Parser(
 """
 struct S { int f; };
-S v = new S;
+!S !v = new S;
 S t = new S;
 while(arg) {
     arg=arg-1;
@@ -477,7 +477,7 @@ while(arg) {
 return arg;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop23,arg,Phi(Region50,.f,0));", stop.toString());
+        assertEquals("return 0;", stop.toString());
     }
 
     @Test
@@ -485,7 +485,7 @@ return arg;
         Parser parser = new Parser(
 """
 struct S { int f; };
-S v = new S;
+!S !v = new S;
 S t = new S;
 if (arg) {
     v.f=2;
@@ -503,7 +503,7 @@ return v;
         Parser parser = new Parser(
 """
 struct S { int f; };
-S v = new S;
+!S !v = new S;
 int i = arg;
 while (arg > 0) {
     int j = i/3;
diff --git a/src/test/java/com/seaofnodes/simple/Chapter14FloatTest.java b/src/test/java/com/seaofnodes/simple/Chapter14FloatTest.java
index c42b0154..3d92c9cf 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter14FloatTest.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter14FloatTest.java
@@ -84,7 +84,7 @@ while( 1 ) {
 return guess;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop10,(flt)arg,(((ToFloat/Phi_guess)+Phi_guess)/2.0));", stop.toString());
+        assertEquals("return Phi(Loop,(flt)arg,(((ToFloat/Phi_guess)+Phi_guess)/2.0));", stop.toString());
         assertEquals(3.0, Evaluator.evaluate(stop,  9));
         assertEquals(1.414213562373095, Evaluator.evaluate(stop,  2));
     }
diff --git a/src/test/java/com/seaofnodes/simple/Chapter14Test.java b/src/test/java/com/seaofnodes/simple/Chapter14Test.java
index be9b1fd4..27804a5a 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter14Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter14Test.java
@@ -61,7 +61,7 @@ while( b ) b = b + 456;// Truncate
 return b;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Loop10,123,((Phi_b+456)&255));", stop.toString());
+        assertEquals("return 0;", stop.toString());
     }
 
     @Test
@@ -96,7 +96,7 @@ return b;
         Parser parser = new Parser(
 """
 struct Foo { u1 b; };
-Foo f = new Foo;
+!Foo !f = new Foo;
 f.b = 123;
 return f.b;
 """);
@@ -177,7 +177,7 @@ while(v1) break;
 return v1;
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("return (Phi(Loop17,((1<<arg)&1),0)&Phi(Loop,Shl,4294967295));", stop.toString());
+        assertEquals("return Phi(Loop,(((1<<arg)&1)&Shl),0);", stop.toString());
         assertEquals(1L, Evaluator.evaluate(stop,  0));
     }
 
diff --git a/src/test/java/com/seaofnodes/simple/Chapter15Test.java b/src/test/java/com/seaofnodes/simple/Chapter15Test.java
index 63bdcce7..452a1051 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter15Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter15Test.java
@@ -25,8 +25,8 @@ return 3.14;
     public void testCyclic() {
         Parser parser = new Parser(
 """
-struct C { C? l; };
-C c = new C;
+struct C { !C? !l; };
+!C !c = new C;
 c.l = c;
 return c;
 """);
@@ -40,7 +40,7 @@ return c;
         Parser parser = new Parser(
 """
 u8[] old = new u8[0];
-u8[] output = new u8[1];
+u8[] !output = new u8[1];
 int i = 0;
 while (i < old#) {
     output[i] = old[i];
@@ -83,7 +83,7 @@ return is[1];
     public void testBasic3() {
         Parser parser = new Parser(
 """
-int[] a = new int[2];
+int[] !a = new int[2];
 a[0] = 1;
 a[1] = 2;
 return a[0];
@@ -98,7 +98,7 @@ return a[0];
         Parser parser = new Parser(
 """
 struct A { int i; };
-A?[] a = new A?[2];
+!A?[] !a = new !A?[2];
 return a;
 """);
         StopNode stop = parser.parse().iterate();
@@ -112,16 +112,16 @@ return a;
 """
 struct S { int x; flt y; };
 // A new S
-S s = new S; s.x=99; s.y = 3.14;
+!S !s = new S; s.x=99; s.y = 3.14;
 
 // Double-d array of Ss.  Fill in one row.
-S?[]?[] iss = new S?[]?[2];
-iss[0] = new S?[7];
+!S?[]?[] !iss = new !S?[]?[2];
+iss[0] = new !S?[7];
 iss[0][2] = s;
 
 // Now pull out the filled-in value, with null checks
 flt rez;
-S?[]? is = iss[arg];
+!S?[]? is = iss[arg];
 if( !is ) rez = 1.2;
 else {
     S? i = is[2];
@@ -131,24 +131,22 @@ else {
 return rez;
 """);
         StopNode stop = parser.parse().iterate();
-        // Shared allocation memory prevents folding the field Store into New.
-        assertEquals("return Phi(Region121,1.2,Phi(Region118,2.3,.y));", stop.toString());
+        assertEquals("return Phi(Region,1.2,Phi(Region,2.3,.y));", stop.toString());
         assertEquals(3.14, Evaluator.evaluate(stop, 0));
         assertEquals(1.2 , Evaluator.evaluate(stop, 1));
     }
 
-    @Ignore
     @Test
     public void testBasic6() {
         Parser parser = new Parser(
 """
 struct S { int x; flt y; };
 // A new S
-S s = new S; s.x=99; s.y = 3.14;
+!S !s = new S; s.x=99; s.y = 3.14;
 
 // Double-d array of Ss.  Fill in one row.
-S?[]?[] iss = new S?[]?[2];
-iss[0] = new S?[7];
+!S?[]?[] iss = new !S?[]?[2];
+iss[0] = new !S?[7];
 iss[0][2] = s;
 
 // Now pull out the filled-in value, with null checks
@@ -158,9 +156,8 @@ if( iss[arg] )
         rez = iss[arg][2].y;
 return rez;
 """);
-        StopNode stop = parser.parse().iterate();
-        assertEquals("return Phi(Region122,Phi(Region118,.y,1.2),1.2);", stop.toString());
-        assertEquals(3.14, Evaluator.evaluate(stop, 0));
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Might be null accessing '[]'",e.getMessage()); }
     }
 
     @Test
@@ -168,9 +165,9 @@ return rez;
         Parser parser = new Parser(
 """
 // Can we define a forward-reference array?
-struct Tree { Tree?[]? _kids; };
-Tree root = new Tree;
-root._kids = new Tree?[2];
+struct Tree { !Tree?[]? !_kids; };
+!Tree !root = new Tree;
+root._kids = new !Tree?[2]; // NO BANG SO ARRAY IS OF IMMUTABLE TREES????
 root._kids[0] = new Tree;
 return root;
 """);
@@ -183,7 +180,7 @@ return root;
     public void testNestedStructAddMemProj() {
         Parser parser = new Parser(
 """
-struct S { int a; int[] b; };
+struct S { int a; int[] !b; };
 return 0;
 """);
         StopNode stop = parser.parse();
@@ -194,7 +191,7 @@ return 0;
     public void testRollingSum() {
         Parser parser = new Parser(
 """
-int[] ary = new int[arg];
+int[] !ary = new int[arg];
 // Fill [0,1,2,3,4,...]
 int i=0;
 while( i < ary# ) {
@@ -218,44 +215,42 @@ return ary[1] * 1000 + ary[3]; // 1 * 1000 + 6
     public void sieveOEratosthenes() {
         Parser parser = new Parser(
 """
-int[] ary = new int[arg];
-int[] primes = new int[arg];
-int nprimes = 0;
-// Find primes
-int j=2;
-while( j*j < arg ) {
-    while( ary[j]==1 ) j = j + 1;
-    // j is now a prime
-    primes[nprimes] = j;  nprimes = nprimes + 1;
+int[] !ary = new int[arg], !primes = new int[arg];
+int nprimes = 0, p=2;
+// Find primes while p^2 < arg
+while( p*p < arg ) {
+    // skip marked non-primes
+    while( ary[p]==1 ) p = p + 1;
+    // p is now a prime
+    primes[nprimes] = p;  nprimes = nprimes + 1;
     // Mark out the rest non-primes
-    int i = j + j;
+    int i = p + p;
     while( i < ary# ) {
         ary[i] = 1;
-        i = i + j;
+        i = i + p;
     }
-    j = j + 1;
+    p = p + 1;
 }
-// Now just collect the remaining primes
-while( j < arg ) {
-    if( ary[j] == 0 ) {
-        primes[nprimes] = j;  nprimes = nprimes + 1;
+// Now just collect the remaining primes, no more marking
+while( p < arg ) {
+    if( ary[p] == 0 ) {
+        primes[nprimes] = p;  nprimes = nprimes + 1;
     }
-    j = j + 1;
+    p = p + 1;
 }
-// Shrink the result array to size
-int[] rez = new int[nprimes];
-j = 0;
+// Copy/shrink the result array
+int[] !rez = new int[nprimes];
+int j = 0;
 while( j < nprimes ) {
     rez[j] = primes[j];
     j = j + 1;
 }
-
 return rez;
 """);
         StopNode stop = parser.parse().iterate();
         assertEquals("return [int];", stop.toString());
         Evaluator.Obj obj = (Evaluator.Obj)Evaluator.evaluate(stop, 20);
-        assertEquals("[int] {  # :int;   [] :int; }",obj.struct().toString());
+        assertEquals("[int] {int #; int ![]; }",obj.struct().toString());
         long nprimes = (Long)obj.fields()[0];
         long[] primes = new long[]{2,3,5,7,11,13,17,19};
         for( int i=0; i<nprimes; i++ )
@@ -267,8 +262,8 @@ return rez;
         Parser parser = new Parser(
 """
 struct S {int i; flt f;};
-S s1 = new S;
-S s2 = new S;
+!S !s1 = new S;
+!S !s2 = new S;
 s2.i = 3;
 s2.f = 2.0;
 if (arg) s1 = new S;
diff --git a/src/test/java/com/seaofnodes/simple/Chapter16Test.java b/src/test/java/com/seaofnodes/simple/Chapter16Test.java
index 3d3708dc..996be2a1 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter16Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter16Test.java
@@ -9,15 +9,6 @@ import static org.junit.Assert.fail;
 
 public class Chapter16Test {
 
-    @Test
-    public void testRequiredReference() {
-        for( String fields : new String[] { "int[] x;" } ) {
-            String src = "struct Point { "+fields+" }; Point p = new Point; p.x=p.x+1; return p;";
-            try { new Parser(src).parse().iterate(); fail(fields); }
-            catch( Exception e ) { assertEquals("'Point' is not fully initialized, field 'x' needs to be set in a constructor",e.getMessage()); }
-        }
-    }
-
     @Ignore
     @Test
     public void testJig() {
@@ -55,9 +46,6 @@ return x+y;
     }
 
 
-
-
-
     @Test
     public void testConstruct0() {
         Parser parser = new Parser("""
@@ -70,8 +58,6 @@ return z.x;
         assertEquals(3L, Evaluator.evaluate(stop,  0));
     }
 
-
-
     @Test
     public void testConstruct2() {
         Parser parser = new Parser("""
@@ -85,16 +71,12 @@ return z.x;
     }
 
 
-
-
-    // Same as the Chapter13 test with the same name, but using the new
-    // constructor syntax
     @Test
     public void testLinkedList1() {
         Parser parser = new Parser(
 """
-struct LLI { LLI? next; int i; };
-LLI? head = null;
+struct LLI { !LLI? !next; int i; };
+!LLI? !head = null;
 while( arg ) {
     head = new LLI { next=head; i=arg; };
     arg = arg-1;
@@ -115,13 +97,13 @@ return next.i;
     public void testLinkedList2() {
         Parser parser = new Parser(
 """
-struct LLI { LLI? next; int i; };
-LLI? head = null;
+struct LLI { !LLI? !next; int i; };
+!LLI? !head = null;
 while( arg ) {
     head = new LLI {
         next=head;
         // Any old code in the constructor
-        int tmp=arg;
+        int !tmp=arg;
         while( arg > 10 ) {
             tmp = tmp + arg;
             arg = arg - 1;
@@ -147,11 +129,11 @@ return next.i;
         Parser parser = new Parser(
 """
 struct Square {
-    flt side = arg;
+    flt !side = arg;
     // Newtons approximation to the square root, computed in a constructor.
     // The actual allocation will copy in this result as the initial
     // value for 'diag'.
-    flt diag = arg*arg/2;
+    flt !diag = arg*arg/2;
     while( 1 ) {
         flt next = (side/diag + diag)/2;
         if( next == diag ) break;
@@ -168,13 +150,13 @@ return new Square;
     static final String CONSTRUCTOR_MEMORY = """
         struct S { int x; int y; };
         struct T { int z=arg+40; };
-        T t = new T;
-        S a = new S { x=11; y=7; };
-        S b = new S { x=22; y=9; };
-        S p=a;
+        !T !t = new T;
+        !S !a = new S { x=11; y=7; };
+        !S !b = new S { x=22; y=9; };
+        !S !p=a;
         if (arg) p=b;
         int before=p.x;
-        S c = new S {
+        !S !c = new S {
             x=p.x+1;
             { int i=0; while (i<2) { p.y=p.y+1; i=i+1; } }
             y=p.y;
diff --git a/src/test/java/com/seaofnodes/simple/Chapter17aTest.java b/src/test/java/com/seaofnodes/simple/Chapter17aTest.java
new file mode 100644
index 00000000..7d61a913
--- /dev/null
+++ b/src/test/java/com/seaofnodes/simple/Chapter17aTest.java
@@ -0,0 +1,107 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.evaluator.Evaluator;
+import com.seaofnodes.simple.node.StopNode;
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter17aTest {
+
+    @Test
+    public void testFinal1() {
+        Parser parser = new Parser(
+"""
+int x=2, y=3;
+if( arg ) { int x = y; x = x*x; y=x; } // Shadow final x
+return y;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return Phi(Region,9,3);", stop.toString());
+        assertEquals(3L, Evaluator.evaluate(stop, 0));
+        assertEquals(9L, Evaluator.evaluate(stop, 1));
+    }
+
+    @Test
+    public void testConstruct1() {
+        Parser parser = new Parser("""
+struct X { int ~x; };
+X z = new X { x=3; };
+return z.x;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 3;", stop.toString());
+        assertEquals(3L, Evaluator.evaluate(stop,  0));
+    }
+
+    @Test
+    public void testStructFinal0() {
+        Parser parser = new Parser("""
+struct Point { int ~x, ~y; };
+Point p = new Point { x=3; y=4; };
+return p;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return (const)Point;", stop.toString());
+        assertEquals("Obj<Point>{x=3,y=4}", Evaluator.evaluate(stop,  0).toString());
+    }
+
+    @Test
+    public void testStructFinal1() {
+        Parser parser = new Parser("""
+struct Point { int x=3, y=4; };
+Point p = new Point { x=5; y=6; };
+p.x=p.x+1;
+return p;
+""");
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal2() {
+        Parser parser = new Parser("""
+struct Point { int x=3, y=4; };
+Point p = new Point;
+p.x=p.x+1;
+return p;
+""");
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal3() {
+        for( String fields : new String[] { "int ~x; int ~y;", "int[] !x;", "int[] !x;" } ) {
+            String src = "struct Point { "+fields+" }; Point p = new Point; p.x=p.x+1; return p;";
+            try { new Parser(src).parse().iterate(); fail(fields); }
+            catch( Exception e ) { assertEquals("'Point' is not fully initialized, field 'x' needs to be set in a constructor",e.getMessage()); }
+        }
+    }
+
+    @Test
+    public void testStructFinal4() {
+        Parser parser = new Parser("""
+struct Point { int ~x=3; int ~y=4; };
+Point p = new Point;
+p.x=p.x+1;
+return p;
+""");
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal5() {
+        Parser parser = new Parser("""
+struct Point { int x=3; int y=4; };
+!Point !p = new Point;
+p.x=p.x+1;
+return p;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return Point;", stop.toString());
+        assertEquals("Obj<Point>{x=4,y=4}", Evaluator.evaluate(stop,  0).toString());
+    }
+
+}
diff --git a/src/test/java/com/seaofnodes/simple/MutabilityTest.java b/src/test/java/com/seaofnodes/simple/MutabilityTest.java
new file mode 100644
index 00000000..3442c54a
--- /dev/null
+++ b/src/test/java/com/seaofnodes/simple/MutabilityTest.java
@@ -0,0 +1,57 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class MutabilityTest {
+    private static void ok(String src, String result) {
+        var stop = new Parser(src).parse().iterate();
+        assertEquals(result,com.seaofnodes.simple.evaluator.Evaluator.evaluate(stop,0).toString());
+    }
+    private static void bad(String src) {
+        try {
+            new Parser(src).parse().iterate();
+        } catch( RuntimeException expected ) {
+            String msg = expected.getMessage();
+            assertTrue("Expected a permission error, got: "+expected,
+                msg!=null && (msg.contains("final") || msg.contains("not of declared type") || msg.contains("Cannot store")));
+            return;
+        }
+        fail("Accepted forbidden write: "+src);
+    }
+
+    @Test public void testIndependentBindingsAndViews() {
+        ok("struct P { int x; }; !P ~p=new P; p.x=7; return p.x;", "7");
+        ok("struct P { int x; }; ~P !p=new P{x=3;}; p=new P{x=7;}; return p.x;", "7");
+        bad("struct P { int x; }; !P ~p=new P; p=new P; return 0;");
+        bad("struct P { int x; }; ~P !p=new P; p.x=7; return 0;");
+        bad("int ~x=3; x=7; return x;");
+        ok("int !x=3; x=7; return x;", "7");
+    }
+
+    @Test public void testDeepViewAndAliases() {
+        ok("struct P { int x; }; !P ~p=new P; ~P ~r=p; p.x=7; return r.x;", "7");
+        bad("struct P { int x; }; struct Box { !P p; }; !P q=new P; Box b=new Box{p=q;}; b.p.x=7; return 0;");
+        bad("struct P { int x; }; P p=new P; !P q=p; q.x=7; return 0;");
+        bad("struct P { P? next; int x; }; !P p=new P{next=new P;}; p.next.x=7; return 0;");
+        bad("struct P { !P? next; int x; }; P p=new P{next=new P;}; p.next.x=7; return 0;");
+    }
+
+    @Test public void testConstructorScope() {
+        ok("struct P { int ~x; }; P p=new P{if(arg) x=3; else x=7;}; return p.x;", "7");
+        bad("int ~outer=1; struct P { int x; }; P p=new P{outer=7;}; return outer;");
+        bad("struct P { int x; }; P p=new P{int ~local=1; local=7;}; return p.x;");
+    }
+
+    @Test public void testArrayLayers() {
+        bad("struct P { int x; }; !P?[] rw=new !P?[1]; P?[] ro=rw; rw[0]=new P; ro[0].x=7; return 0;");
+        ok("u8[] a=new u8[2]; a[0]=7; return a[0];", "7");
+        ok("struct P { int x; }; P?[] a=new P?[1]; a[0]=new P{x=7;}; return a[0].x;", "7");
+        bad("struct P { int x; }; P?[] a=new P?[1]; a[0]=new P; a[0].x=7; return 0;");
+        ok("struct P { int x; }; !P?[] a=new !P?[1]; a[0]=new P; a[0].x=7; return a[0].x;", "7");
+        bad("u8[~] a=new u8[1]; a[0]=7; return 0;");
+        ok("u8[~]?[] rows=new u8[~]?[1]; rows[0]=new u8[1]; return rows#;", "1");
+        bad("u8[~]?[] rows=new u8[~]?[1]; rows[0]=new u8[1]; rows[0][0]=7; return 0;");
+        bad("u8[]?[~] rows=new u8[]?[1]; rows[0]=new u8[1]; return 0;");
+    }
+}
diff --git a/src/test/java/com/seaofnodes/simple/SchedulerTest.java b/src/test/java/com/seaofnodes/simple/SchedulerTest.java
index 4b692f51..d8a22fd3 100644
--- a/src/test/java/com/seaofnodes/simple/SchedulerTest.java
+++ b/src/test/java/com/seaofnodes/simple/SchedulerTest.java
@@ -24,7 +24,7 @@ public class SchedulerTest {
 struct S {
     int f;
 }
-S v=new S;
+!S !v=new S;
 v.f = 2;
 int i=v.f;
 if (arg) v.f=1;
@@ -41,7 +41,7 @@ return i;
 struct S {
     int f;
 };
-S v0=new S;
+!S !v0=new S;
 if(arg) v0.f=1;
 return v0;
 """);
@@ -57,7 +57,7 @@ return v0;
 struct S {
     int f;
 };
-S v=new S;
+!S !v=new S;
 v.f = 2;
 int i=new S.f;
 i=v.f;
diff --git a/src/test/java/com/seaofnodes/simple/TypeTest.java b/src/test/java/com/seaofnodes/simple/TypeTest.java
index 6f7409cd..3fac1641 100644
--- a/src/test/java/com/seaofnodes/simple/TypeTest.java
+++ b/src/test/java/com/seaofnodes/simple/TypeTest.java
@@ -20,7 +20,7 @@ public class TypeTest {
                 Field.make("b", TypeInteger.BOT,-4, false) });
         Assert.assertEquals(s1, s1.glb());
         Assert.assertNotEquals(s1, s1.dual());
-        Assert.assertEquals(s1, s1.dual().glb());
+        Assert.assertEquals(s1.makeRO(), s1.dual().glb());
 
         TypeMem m1 = TypeMem.make(1,TypeInteger.ZERO);
         TypeMem m2 = TypeMem.make(2,TypeInteger.U16);
@@ -54,12 +54,12 @@ public class TypeTest {
 
         Assert.assertNotEquals(ptr1, ptr2);
         Assert.assertNotEquals(ptr1, ptr1.glb());
-        Assert.assertEquals(ptr1nil, ptr1.glb());
+        Assert.assertEquals(ptr1nil.withAccess(true), ptr1.glb());
 
         Assert.assertEquals(ptr1, ptr1.dual().dual());
-        Assert.assertEquals(ptr1.glb(), ptr1.dual().glb());
-        Assert.assertEquals(TypeMemPtr.make(TypeStruct.BOT,true), ptr1.meet(ptr2nil));
-        Assert.assertEquals(ptr1.glb(), ptr1.meet(TypeMemPtr.NULLPTR));
+        Assert.assertEquals(ptr1.glb().makeFrom(s1.dual().glb()), ptr1.dual().glb());
+        Assert.assertEquals(TypeMemPtr.make(TypeStruct.BOT,true).withAccess(false), ptr1.meet(ptr2nil));
+        Assert.assertEquals(ptr1nil, ptr1.meet(TypeMemPtr.NULLPTR));
 
         TypeMemPtr TOP = TypeMemPtr.TOP;
         TypeMemPtr BOT = TypeMemPtr.make(TypeStruct.BOT,true );
@@ -68,7 +68,7 @@ public class TypeTest {
         Type PTR_meet_NULL = NULL.meet(PTR);
         Assert.assertEquals(BOT, PTR_meet_NULL);
         Type ptr1_meet_ptr2 = ptr1.meet(ptr2);
-        Assert.assertEquals(PTR, ptr1_meet_ptr2);
+        Assert.assertEquals(PTR.withAccess(false), ptr1_meet_ptr2);
         Type NULL_join_ptr1 = NULL.join(ptr1);
         Assert.assertEquals(TOP, NULL_join_ptr1);
         Type NULL_join_PTR = PTR.join(NULL);
@@ -79,7 +79,7 @@ public class TypeTest {
 
     // Test theoretical properties.
     // This is a symmetric complete bounded (ranked) lattice.
-    // Also the meet is commutative and associative.
+    // Also, the meet is commutative and associative.
     // The lattice has a dual (symmetric), and join is ~(~x meet ~y).
     // See https://en.wikipedia.org/wiki/Lattice_(order).
     @Test
diff --git a/src/test/java/com/seaofnodes/simple/evaluator/Evaluator.java b/src/test/java/com/seaofnodes/simple/evaluator/Evaluator.java
index 8b530307..0721402f 100644
--- a/src/test/java/com/seaofnodes/simple/evaluator/Evaluator.java
+++ b/src/test/java/com/seaofnodes/simple/evaluator/Evaluator.java
@@ -36,7 +36,7 @@ public class Evaluator {
                 sb.append("obj@").append(cid);
                 return id;
             }
-            if (struct._name.equals("u8[]")) {
+            if (struct._name.equals("[u8]")) {
                 sb.append('"');
                 for (int i=struct._fields.length-1; i<fields.length; i++) {
                     var v = fields[i];
@@ -306,6 +306,7 @@ public class Evaluator {
             case NewNode      alloc -> alloc(alloc);
             case CProjNode    cproj -> ((Object[])val(cproj.ctrl()))[cproj._idx];
             case ProjNode     proj  -> ((Object[])val( proj.in(0) ))[ proj._idx];
+            case ReadOnlyNode ro    -> val(ro.in(1));
             default                 -> throw new AssertionError("Unexpected node " + node);
         };
     }
diff --git a/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java b/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java
index d3cbb0ee..183dcb84 100644
--- a/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java
+++ b/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java
@@ -479,7 +479,7 @@ public class ScriptGenerator {
         for (int i=0; i<fields.length; i++) {
             var fieldName = getRandomName();
             var type = getType(true);
-            printIndentation().append(type.name).append(" ").append(fieldName).append(";\n");
+            printIndentation().append(declType(type)).append(" !").append(fieldName).append(";\n");
             fields[i] = new TypeStruct.Field(fieldName.toString(), type, struct);
         }
         indentation -= INDENTATION;
@@ -676,14 +676,16 @@ public class ScriptGenerator {
         return 0;
     }
 
-    /**
-     * Generate a declaration statement.
-     * @return 0
-     */
+    // This generator mutates references and fields; request both permissions.
+    private static String declType(Type type) {
+        return (type instanceof TypeStruct || type instanceof TypeNullable ? "!" : "") + type.name;
+    }
+
+    /** Generate a declaration statement. */
     public int genDecl() {
         var type = getType();
         var name = getVarName();
-        sb.append(generateInvalid() ? getRandomName() : type.name).append(" ").append(name);
+        sb.append(generateInvalid() ? getRandomName() : declType(type)).append(" !").append(name);
         if (!(type instanceof TypeNullable) || random.nextBoolean()) {
             sb.append("=");
             genExpression(type, true);