I didn't knew MPS but indeed seems quite similar. Both are structured editors, in the sense that you never work with "text" but with some projection of the unde

I didn't knew MPS but indeed seems quite similar. Both are structured editors, in the sense that you never work with "text" but with some projection of the underlying tree structure. For example you can ask TeXmacs to show you a representation where every node tree is explicit (which look very much HTML, but where you cannot have an open environment tag without the corresponding closing tag).