         writeOutput()
 catch ex
     console.error("Error: " + ex.message)
-    process.exit(1)
+    process.exit(
+        if ex.message.startsWith("NV: ")
+            64
+        else
+            1
+    )

            i++
        else if arg == "-n"
            negation = args[i + 1].match(/^((?:\*\/)?)([^*]+)(\*?)$/)
            assert(negation != null)
            negations.push(negation)
            i += 2
        else if arg in ["--version", "-v"]

            compileCommands[arg.split(":")[1]] = args[i + 1]
            i += 2
        else if arg == "-d"
            assert(
                args[i + 1].search(/^(\/|\.\/|\.\.\/)/) == -1,
                "Dummy can't start with `/`, `./` or `../`."
            )
            dummies.push(args[i + 1])
            i += 2
        else if arg == "-i"
