OpenEuphoria

To be clear, Euphoria DOES pass by reference but it copies on write. So there is a performance advantage there.

As for manipulating large data structs, in Euphoria you currently have to implement them as file-level or global variables for efficiency.

One thought that I've had for implementing a new language is that functions should be pass by reference/copy on write, but procedures should be pass by reference/modify in place.