new exceptions

src/main/java/typechecker/AssignmentTypeMismatchException.java

@@ -0,0 +1,8 @@
+package typechecker;
+
+public class AssignmentTypeMismatchException extends RuntimeException {
+
+    public AssignmentTypeMismatchException(String message) {
+        super(message);
+    }
+}

src/main/java/typechecker/OperatorTypeMismatchException.java

@@ -0,0 +1,8 @@
+package typechecker;
+
+public class OperatorTypeMismatchException extends RuntimeException {
+
+    public OperatorTypeMismatchException(String message) {
+        super(message);
+    }
+}

src/main/java/typechecker/OperatorUsageException.java

@@ -0,0 +1,8 @@
+package typechecker;
+
+public class OperatorUsageException extends RuntimeException {
+
+    public OperatorUsageException(String message) {
+        super(message);
+    }
+}