Earlier versions of Mx used backspace statements to re-read data. These have been eliminated so that Mx may be run interactively. This feature is primarily to facilitate communication with the frontend which is under development. However, it might be used in a multiple window environment to keep the Mx kernel resident while different jobs (perhaps in multiple fit mode) are supplied. The output is pasted to the same screen and it can be interweaved with the input in a rather strange fashion, depending on how fast you paste.
This feature allows new and interesting things with vl files which are documented in the draft paper "A note on latent variable models when the paths are observed data.' Since definition variables are referenced through negative parameter specification numbers, only positive parameter specification numbers may be used for the usual purposes.
Mike Neale, email@example.com, Medical College of VA