Chapter 17b: Syntax Sugarlinear-chapter17b

6 files changed, 665 insertions, 10 deletions

diff --git a/src/test/java/com/seaofnodes/simple/BrainFuckTest.java b/src/test/java/com/seaofnodes/simple/BrainFuckTest.java
new file mode 100644
index 00000000..154b74a2
--- /dev/null
+++ b/src/test/java/com/seaofnodes/simple/BrainFuckTest.java
@@ -0,0 +1,72 @@
+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 + """
+var d = 0;
+u8[] !output = new u8[0];
+u8[] !data = new u8[100];
+
+for( int pc = 0; pc < program#; pc++ ) {
+    var command = program[pc];
+    if (command == 62) {
+        d++;
+    } else if (command == 60) {
+        d--;
+    } else if (command == 43) {
+        data[d]++;
+    } else if (command == 45) {
+        data[d]--;
+    } else if (command == 46) {
+        // Output a byte; increase the output array size
+        var old = output;
+        output = new u8[output# + 1];
+        for( var i = 0; i < old#; i++ )
+            output[i] = old[i];
+        output[old#] = data[d]; // Add the extra byte on the end
+    } else if (command == 44) {
+        data[d] = 42;
+    } else if (command == 91) {
+        if (data[d] == 0) {
+            for( var d = 1; d > 0; ) {
+                command = program[++pc];
+                if (command == 91) d++;
+                if (command == 93) d--;
+            }
+        }
+    } else if (command == 93) {
+        if (data[d]) {
+            for( var d = 1; d > 0; ) {
+                command = program[--pc];
+                if (command == 93) d++;
+                if (command == 91) d--;
+            }
+        }
+    }
+}
+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/Chapter13Test.java b/src/test/java/com/seaofnodes/simple/Chapter13Test.java
index 695777e2..8f64701f 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter13Test.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter13Test.java
@@ -293,7 +293,7 @@ else {
 }
 """);
         StopNode stop = parser.parse().iterate();
-        assertEquals("Stop[ return 9; return 0; return 0; ]", stop.toString());
+        assertEquals("Stop[ return 9; return 0; return 0; return 0; return 0; ]", stop.toString());
     }
 
 
diff --git a/src/test/java/com/seaofnodes/simple/Chapter17aTest.java b/src/test/java/com/seaofnodes/simple/Chapter17aTest.java
index 7d61a913..423eade0 100644
--- a/src/test/java/com/seaofnodes/simple/Chapter17aTest.java
+++ b/src/test/java/com/seaofnodes/simple/Chapter17aTest.java
@@ -51,7 +51,7 @@ return p;
         Parser parser = new Parser("""
 struct Point { int x=3, y=4; };
 Point p = new Point { x=5; y=6; };
-p.x=p.x+1;
+p.x++;
 return p;
 """);
         try { parser.parse().iterate(); fail(); }
@@ -63,7 +63,7 @@ return p;
         Parser parser = new Parser("""
 struct Point { int x=3, y=4; };
 Point p = new Point;
-p.x=p.x+1;
+p.x++;
 return p;
 """);
         try { parser.parse().iterate(); fail(); }
@@ -72,8 +72,8 @@ return p;
 
     @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;";
+        for( String fields : new String[] { "var x; var y;", "int[] !x;", "int[] !x;" } ) {
+            String src = "struct Point { "+fields+" }; Point p = new Point; p.x++; 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()); }
         }
@@ -82,21 +82,21 @@ return p;
     @Test
     public void testStructFinal4() {
         Parser parser = new Parser("""
-struct Point { int ~x=3; int ~y=4; };
+struct Point { val x=3; val y=4; };
 Point p = new Point;
-p.x=p.x+1;
+p.x++;
 return p;
 """);
         try { parser.parse().iterate(); fail(); }
-        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+        catch( Exception e ) { assertEquals("Cannot reassign final 'x'",e.getMessage()); }
     }
 
     @Test
     public void testStructFinal5() {
         Parser parser = new Parser("""
-struct Point { int x=3; int y=4; };
+struct Point { var x=3; var y=4; };
 !Point !p = new Point;
-p.x=p.x+1;
+p.x++;
 return p;
 """);
         StopNode stop = parser.parse().iterate();
diff --git a/src/test/java/com/seaofnodes/simple/Chapter17bTest.java b/src/test/java/com/seaofnodes/simple/Chapter17bTest.java
new file mode 100644
index 00000000..976691fc
--- /dev/null
+++ b/src/test/java/com/seaofnodes/simple/Chapter17bTest.java
@@ -0,0 +1,500 @@
+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 static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter17bTest {
+
+    @Test
+    public void testJig() {
+        Parser parser = new Parser("return 1;");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 1;", stop.toString());
+        assertEquals(1L, Evaluator.evaluate(stop,  0));
+    }
+
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testInc0() {
+        Parser parser = new Parser("""
+return arg++;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return arg;", stop.toString());
+        assertEquals(0L, Evaluator.evaluate(stop, 0));
+    }
+
+    @Test
+    public void testInc1() {
+        Parser parser = new Parser("""
+return arg+++arg++;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return ((arg*2)+1);", stop.toString());
+        assertEquals(1L, Evaluator.evaluate(stop, 0));
+    }
+
+    @Test
+    public void testInc2() {
+        Parser parser = new Parser("""
+//   -(arg--)-(arg--)
+return -arg---arg--;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return (-((arg*2)+-1));", stop.toString());
+        assertEquals(1L, Evaluator.evaluate(stop, 0));
+    }
+
+    @Test
+    public void testInc3() {
+        Parser parser = new Parser("""
+int[] !xs = new int[arg];
+xs[0]++;
+xs[1]++;
+return xs[0];
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 1;", stop.toString());
+        assertEquals(1L, Evaluator.evaluate(stop, 2));
+    }
+
+    @Test
+    public void testInc4() {
+        Parser parser = new Parser("""
+u8[] !xs = new u8[1];
+xs[0]--;
+return xs[0];
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 255;", stop.toString());
+        assertEquals(255L, Evaluator.evaluate(stop, 2));
+    }
+
+    @Test
+    public void testInc5() {
+        Parser parser = new Parser("""
+struct S { u16 x; };
+!S !s = new S;
+s.x--;
+return s.x;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 65535;", stop.toString());
+        assertEquals(65535L, Evaluator.evaluate(stop, 2));
+    }
+
+    @Test
+    public void testInc6() {
+        Parser parser = new Parser("return --arg;");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return (arg+-1);", stop.toString());
+        assertEquals(-1L, Evaluator.evaluate(stop, 0));
+    }
+
+    @Test
+    public void testInc7() {
+        Parser parser = new Parser("u8 x=0; return --x;");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 255;", stop.toString());
+        assertEquals(255L, Evaluator.evaluate(stop, 0));
+    }
+
+    @Test
+    public void testInc8() {
+        Parser parser = new Parser("int x; x+=2; return x+=3;");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 5;", stop.toString());
+        assertEquals(5L, Evaluator.evaluate(stop, 0));
+    }
+
+    // ---------------------------------------------------------------
+    @Test public void testVar0() {
+        Parser parser = new Parser("var d; return d;");
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Syntax error, expected =expression: ;",e.getMessage()); }
+    }
+
+    @Test public void testVar1() {
+        Parser parser = new Parser("val d; return d;");
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Syntax error, expected =expression: ;",e.getMessage()); }
+    }
+
+    @Test public void testVar2() {
+        Parser parser = new Parser("int x; x=3; x++; return x; // Ok, no initializer so x is mutable ");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 4;", stop.toString());
+        assertEquals(4L, Evaluator.evaluate(stop, 0));
+    }
+
+    @Test public void testVar3() {
+        Parser parser = new Parser("int x=3; x++; return x; // Ok, primitive so x is mutable despite initializer ");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 4;", stop.toString());
+        assertEquals(4L, Evaluator.evaluate(stop, 0));
+    }
+
+    @Test public void testVar4() {
+        Parser parser = new Parser("struct S{int x;}; !S !s; s=new S; s.x++; return s.x; // Ok, no initializer so x is mutable ");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 1;", stop.toString());
+        assertEquals(1L, Evaluator.evaluate(stop, 0));
+    }
+
+    @Test public void testVar5() {
+        Parser parser = new Parser("struct S{int x;}; !S !s; s=new S{x=3;}; s.x++; return s.x; // Ok, no initializer so x is mutable ");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 4;", stop.toString());
+        assertEquals(4L, Evaluator.evaluate(stop, 0));
+    }
+
+    @Test public void testVar6() {
+        Parser parser = new Parser("struct S{int x;}; S s=new S; s.x++; return s.x; // Error initializer so x is immutable ");
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test public void testVar7() {
+        Parser parser = new Parser("struct S{int x;}; S s=new S{x=3;}; s.x++; return s.x; // Error initializer so x is immutable ");
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test public void testVar8() {
+        Parser parser = new Parser("struct S{int x;}; !S !s=new S; s.x++; return s.x; // Ok, has '!' so s.x is mutable ");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 1;", stop.toString());
+        assertEquals(1L, Evaluator.evaluate(stop, 0));
+    }
+
+    @Test public void testVar9() {
+        Parser parser = new Parser("struct S{int x;}; var s=new S; s.x++; return s.x; // Ok, has var so s.x is mutable ");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 1;", stop.toString());
+        assertEquals(1L, Evaluator.evaluate(stop, 0));
+    }
+
+    @Test public void testVar10() {
+        Parser parser = new Parser("struct S{int x;}; ~S s=new S; s.x++; return s.x; // Error, has val so x is immutable ");
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test public void testVar11() {
+        Parser parser = new Parser("""
+struct Bar { int x; };
+!Bar !bar = new Bar;
+bar.x = 3; // Ok, bar is mutable
+
+struct Foo { !Bar? !bar; int y; };
+!Foo !foo = new Foo { bar = bar; };
+foo.bar = bar; // Ok foo is mutable
+foo.bar.x++;   // Ok foo and foo.bar and foo.bar.x are all mutable
+
+~Foo xfoo = foo; // Throw away mutability
+xfoo.bar.x++;   // Error, cannot mutate through xfoo
+ """);
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test public void testVar12() {
+        Parser parser = new Parser("""
+struct Bar { int x; };
+!Bar !bar = new Bar;
+bar.x = 3; // Ok, bar is mutable
+
+struct Foo { !Bar? !bar; int y; };
+!Foo !foo = new Foo;
+foo.bar = bar; // Ok bar is mutable
+foo.bar.x++;   // Ok foo and foo.bar and foo.bar.x are all mutable
+
+~Foo xfoo = foo;        // Throw away mutability
+int x4 = xfoo.bar.x;   // Ok to read through xfoo, gets 4
+foo.bar.x++;           // Bumps to 5
+int x5 = xfoo.bar.x;   // Ok to read through xfoo, gets 5
+return x4*10+x5;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 45;", stop.toString());
+        assertEquals(45L, Evaluator.evaluate(stop, 0));
+    }
+
+    @Test
+    public void testVar13() {
+        Parser parser = new Parser("""
+int i,i++;
+""");
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Redefining name 'i'",e.getMessage()); }
+    }
+
+
+    @Test
+    public void testVar14() {
+        Parser parser = new Parser("""
+struct B {};
+struct A { !B !b; };
+A x = new A {
+    return b; // read before init
+    b = new B;
+};
+""");
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot read uninitialized field 'b'",e.getMessage()); }
+    }
+
+    @Test
+    public void testVar15() {
+        Parser parser = new Parser("""
+struct B {};
+struct A { !B !b; };
+return new A {
+    if (arg) b = new B; // Constructor ends with partial init of b
+}.b;
+""");
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("'A' is not fully initialized, field 'b' needs to be set in a constructor",e.getMessage()); }
+    }
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testTrinary0() {
+        Parser parser = new Parser("""
+return arg ? 1 : 2;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return Phi(Region,1,2);", stop.toString());
+        assertEquals(2L, Evaluator.evaluate(stop, 0));
+        assertEquals(1L, Evaluator.evaluate(stop, 1));
+    }
+
+    @Test
+    public void testTrinary1() {
+        Parser parser = new Parser("""
+return arg ? 0 : arg;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return 0;", stop.toString());
+        assertEquals(0L, Evaluator.evaluate(stop, 0));
+    }
+
+    @Test
+    public void testTrinary2() {
+        Parser parser = new Parser("""
+struct Bar { int x; };
+var b = arg ? new Bar : null;
+return b ? b.x++ + b.x++ : -1;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return Phi(Region,1,-1);", stop.toString());
+        assertEquals(-1L, Evaluator.evaluate(stop, 0));
+        assertEquals( 1L, Evaluator.evaluate(stop, 1));
+    }
+
+    @Test
+    public void testTrinary3() {
+        Parser parser = new Parser("""
+struct Bar { int x; };
+var b = arg ? new Bar;
+return b ? b.x++ + b.x++ : -1;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return Phi(Region,1,-1);", stop.toString());
+        assertEquals(-1L, Evaluator.evaluate(stop, 0));
+        assertEquals( 1L, Evaluator.evaluate(stop, 1));
+    }
+
+    @Test
+    public void testTrinary4() {
+        // This test case will benefit from an unzipping transformation
+        Parser parser = new Parser("""
+struct Bar { !Bar? !next; int x; };
+var b = arg ? new Bar { next = (arg==2) ? new Bar{x=2;}; x=1; };
+return b ? b.next ? b.next.x : b.x; // parses "b ? (b.next ? b.next.x : b.x) : 0"
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return Phi(Region,Phi(Region,.x,.x),0);", stop.toString());
+        assertEquals( 0L, Evaluator.evaluate(stop, 0));
+        assertEquals( 1L, Evaluator.evaluate(stop, 1));
+        assertEquals( 2L, Evaluator.evaluate(stop, 2));
+    }
+
+    @Test
+    public void testTrinary5() {
+        Parser parser = new Parser("""
+flt f=arg?1:1.2;
+return f;   // missing widening
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return Phi(Region,1.0,1.2);", stop.toString());
+        assertEquals(1.2, Evaluator.evaluate(stop,  0));
+    }
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testFor0() {
+        Parser parser = new Parser("""
+int sum=0;
+for( int i=0; i<arg; i++ )
+    sum += i;
+return sum;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return Phi(Loop,0,(Phi_sum+Phi(Loop,0,(Phi_i+1))));", stop.toString());
+        assertEquals(3L, Evaluator.evaluate(stop, 3));
+        assertEquals(45L, Evaluator.evaluate(stop, 10));
+    }
+    @Test
+    public void testFor1() {
+        Parser parser = new Parser("""
+int sum=0, i=0;
+for( ; i<arg; i++ )
+    sum += i;
+return sum;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return Phi(Loop,0,(Phi_sum+Phi(Loop,0,(Phi_i+1))));", stop.toString());
+        assertEquals(3L, Evaluator.evaluate(stop, 3));
+        assertEquals(45L, Evaluator.evaluate(stop, 10));
+    }
+    @Test
+    public void testFor2() {
+        Parser parser = new Parser("""
+int sum=0;
+for( int i=0; ; i++ ) {
+    if( i>=arg ) break;
+    sum += i;
+}
+return sum;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return Phi(Loop,0,(Phi_sum+Phi(Loop,0,(Phi_i+1))));", stop.toString());
+        assertEquals(3L, Evaluator.evaluate(stop, 3));
+        assertEquals(45L, Evaluator.evaluate(stop, 10));
+    }
+    @Test
+    public void testFor3() {
+        Parser parser = new Parser("""
+int sum=0;
+for( int i=0; i<arg; )
+    sum += i++;
+return sum;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return Phi(Loop,0,(Phi_sum+Phi(Loop,0,(Phi_i+1))));", stop.toString());
+        assertEquals(3L, Evaluator.evaluate(stop, 3));
+        assertEquals(45L, Evaluator.evaluate(stop, 10));
+    }
+    @Test
+    public void testFor4() {
+        Parser parser = new Parser("""
+int sum=0;
+for( int i=0; i<arg; i++ )
+    sum += i;
+return i;
+""");
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Undefined name 'i'",e.getMessage()); }
+    }
+    @Test
+    public void testFor5() {
+        Parser parser = new Parser("""
+for(;;arg++;) {}
+""");
+        try { parser.parse().iterate(); fail(); }
+        catch( Exception e ) { assertEquals("Syntax error, expected Unexpected code after expression: ;",e.getMessage()); }
+    }
+
+
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testForward0() {
+        Parser parser = new Parser("""
+struct A{
+    !B? !f1;
+    !B? !f2;
+};
+return new A;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return A;", stop.toString());
+        assertEquals("Obj<A>{f1=null,f2=null}", Evaluator.evaluate(stop).toString());
+    }
+
+    @Test
+    public void testForward1() {
+        Parser parser = new Parser("""
+struct A{
+    !B?[]? !nil_array_of_b;
+    !B?[]  not_array_of_b = new !B?[0];
+};
+return new A.not_array_of_b;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return [*B?];", stop.toString());
+        assertEquals("Obj<[*B?]>{#=0,[]=[]}", Evaluator.evaluate(stop).toString());
+    }
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testLinkedList2() {
+        Parser parser = new Parser("""
+struct LLI { !LLI? !next; int i; };
+!LLI? !head = null;
+while( arg-- )
+    head = new LLI { next=head; i=arg; };
+int sum=0;
+var ptr = head; // A read-only ptr, to be assigned from read-only next fields
+for( ; ptr; ptr = ptr.next )
+    sum += ptr.i;
+return sum;
+""");
+        StopNode stop = parser.parse().iterate();
+        assertEquals("return Phi(Loop,0,(Phi_sum+.i));", stop.toString());
+        assertEquals(45L, Evaluator.evaluate(stop, 10));
+    }
+
+    @Test
+    public void sieveOfEratosthenes() {
+        Parser parser = new Parser(
+"""
+var ary = new bool[arg], primes = new int[arg];
+var nprimes=0, p=0;
+// Find primes while p^2 < arg
+for( p=2; p*p < arg; p++ ) {
+    // skip marked non-primes
+    while( ary[p] ) p++;
+    // p is now a prime
+    primes[nprimes++] = p;
+    // Mark out the rest non-primes
+    for( int i = p + p; i < ary#; i += p )
+        ary[i] = true;
+}
+// Now just collect the remaining primes, no more marking
+for( ; p < arg; p++ )
+    if( !ary[p] )
+        primes[nprimes++] = p;
+// Copy/shrink the result array
+var !rez = new int[nprimes];
+for( int j=0; j<nprimes; j++ )
+    rez[j] = primes[j];
+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());
+        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++ )
+            assertEquals(primes[i],(long)(Long)obj.fields()[i+1]);
+    }
+
+}
diff --git a/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java b/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java
new file mode 100644
index 00000000..0fa4283b
--- /dev/null
+++ b/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java
@@ -0,0 +1,77 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.evaluator.Evaluator;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class CompoundAssignmentTest {
+    private static final String[] OPS = {"&=", "|=", "^=", "<<=", ">>=", ">>>="};
+
+    private static long apply(String op, long lhs, long rhs) {
+        return switch (op) {
+            case "&=" -> lhs & rhs;
+            case "|=" -> lhs | rhs;
+            case "^=" -> lhs ^ rhs;
+            case "<<=" -> lhs << rhs;
+            case ">>=" -> lhs >> rhs;
+            case ">>>=" -> lhs >>> rhs;
+            default -> throw new AssertionError(op);
+        };
+    }
+
+    @Test public void testLocals() {
+        for (String op : OPS)
+            for (long arg : new long[]{-8, 0, 5, 64}) {
+                long expected = apply(op, arg, 3);
+                check("int x=arg; int r=(x " + op + " 3); return x*10+r;",
+                      arg, expected*11);
+            }
+    }
+
+    @Test public void testRhsOnce() {
+        for (String op : OPS) {
+            long expected = apply(op, 5, 1);
+            check("int x=arg; int count=0; int r=(x " + op +
+                  " (count=count+1)); return count*1000+x*10+r;", 5, 1000+expected*11);
+        }
+    }
+
+    @Test public void testNarrowingAndChaining() {
+        check("u8 x=255; x <<= 1; return x;", 0, 254);
+        check("u8 x=255; x ^= 256; return x;", 0, 255);
+        check("int x=1; int y=3; x |= y <<= 2; return x*100+y;", 0, 1312);
+        check("int x=-8; x >>= 65; return x;", 0, -4);
+        check("int x=-8; x >>>= 65; return x;", 0, Long.MAX_VALUE-3);
+    }
+
+    @Test public void testExistingOperators() {
+        check("int x=8; x+=2; x-=1; x*=3; x/=9; return x;", 0, 3);
+        check("int x=arg; int y=x++; int z=x--; return x*100+y*10+z;", 5, 556);
+        check("return (arg << 2) + (arg >> 1) + (arg >>> 1);", 8, 40);
+        check("return arg <= 8;", 8, 1);
+        check("return arg >= 8;", 8, 1);
+    }
+
+    @Test public void testRejectedAssignments() {
+        for (String op : OPS) {
+            rejected("val x=3; x " + op + " 1; return x;");
+            rejected("int x=3; x " + op + " 1.5; return x;");
+        }
+    }
+
+    private static void rejected(String src) {
+        try {
+            check(src, 0, 0);
+            fail("Accepted invalid assignment: " + src);
+        } catch (RuntimeException e) {
+            assertEquals("Must report a language error", RuntimeException.class, e.getClass());
+            assertNotNull(e.getMessage());
+            assertFalse("Must report a language error: " + e, e.getMessage().contains("Not yet implemented"));
+        }
+    }
+
+    private static void check(String src, long arg, long expected) {
+        var stop = new Parser(src).parse().iterate();
+        assertEquals(src, Long.valueOf(expected), Evaluator.evaluate(stop, arg));
+    }
+}
diff --git a/src/test/java/com/seaofnodes/simple/MutabilityTest.java b/src/test/java/com/seaofnodes/simple/MutabilityTest.java
index 3442c54a..8f99a059 100644
--- a/src/test/java/com/seaofnodes/simple/MutabilityTest.java
+++ b/src/test/java/com/seaofnodes/simple/MutabilityTest.java
@@ -37,6 +37,12 @@ public class MutabilityTest {
         bad("struct P { !P? next; int x; }; P p=new P{next=new P;}; p.next.x=7; return 0;");
     }
 
+    @Test public void testInferencePreservesAccess() {
+        ok("struct P { int x; }; val p=new P; p.x=7; return p.x;", "7");
+        bad("struct P { int x; }; val p=new P; p=new P; return 0;");
+        bad("struct P { int x; }; P p=new P; var q=p; q.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;");