Chapter 17b: Syntax Sugarlinear-chapter17b

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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
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+++ 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));
+    }
+}