About two months ago, in my ongoing project to make a
quasiquote operation that allows users to define their own variants of
unquote as macros, I hit a snag. I took some time away from the problem for a couple of months, but lately I’ve come back to pick up where I left off, and the extensible
quasiquote now has a complete implementation. (Here’s the relevant Git commit.) It doesn’t do anything out of the box that other
quasiquote implementations don’t do, but it uses hypersnippets to do it, and as planned, it allows users to define their own alternatives to
To get past the snag I hit, I thought I would need to implement several “selective” operations on hypertees. It turns out I only needed one:
hypertee-zip-selective. This operation makes it possible to zip two hypertees while selectively skipping some of the holes of each one. This makes it easy to store data in some hypertee holes while still treating others as actual holes, which is useful for representing hypersnippet-shaped data besides hypertees themselves.
So, now I have a working implementation of a quasiquotation operator with user-definable
unquote. I should really write a better post at some point describing how this technique works. In order to get to something that’s simple and stable enough to write useful guide materials for, I’m planning to focus next on cleaning up some of the mess I’ve made trying to implement it over the past couple of years.