I've made some progress on implementing metathesis, but the process involves rewriting a lot of the code that does rule application, and there are some complications (the same ones I've had before, mostly - setting the right conditions under which to update the cursor).

But it occurred to me that I might be duplicating work: if I implement what is described in the above post, then I can treat the source pattern (the first part of the transform statement, on the left side of the > ) as a state machine. This would also allow us to make use of some advanced functionality here, though obviously more power can be dangerous. Ensuring that backreferences behave correctly and such could be a challenge. I might just define a subset of the expression language that excludes *, +, and ? metacharacters.

Thoughts, considerations, rude remarks?