negate done 15 pass

Makefile

 CLEAN=mvn clean package
 TEST=java -cp "chocopy-ref.jar:target/assignment.jar" chocopy.ChocoPy --pass=..s --run --dir src/test/data/pa3/sample/ --test
-FILE=None
+FILE=op_logical
 clean:
 	$(CLEAN)
 test:

src/main/java/chocopy/pa3/CodeGenImpl.java

@@ -464,6 +464,27 @@ public class CodeGenImpl extends CodeGenBase {
 
             return null;
         }
+
+        @Override
+        public Void analyze(UnaryExpr unaryExpr) {
+            switch (unaryExpr.operator) {
+                case "-":
+                    if (unaryExpr.getInferredType().equals(SymbolType.INT_TYPE)) {    
+                        backend.emitADDI(SP, SP, -4, "Increment stack ptr for first operand");
+                        unaryExpr.operand.dispatch(this);
+                 
+                        backend.emitLW(T0, SP, 0, "Load operand 2 into t0");
+                        backend.emitADDI(SP, SP, 4, "Decrement stack ptr for first operand");
+                        
+                        backend.emitSUB(T0, ZERO, T0, "Subtract operands");
+                        backend.emitSW(T0, SP, 0, "Push result onto stack");
+                        return null;
+                    }
+            }
+            return null;
+        }
+
+
         @Override
         public Void analyze(AssignStmt assignStmt) {
             return null;