I'm grateful for the author's "other options that were considered" section with eight alternatives to S7. But Embeddable Common Lisp (ECL) is the only one listed that he doesn't write a few sentences about, to contrast its pros and cons versus S7. I'd love to hear more.
The first is that it seemed at the time that Scheme was going to be easier to work with, and that has proven true. It's a lot easier to do music theory hacking and integrate with Max using a lisp 1. Being able to seamlessly change whatever the first form is (function, hash-table, list, vector) with no change to the code has turned out to be really really nice in my work.
The second was that when I started I knew little about Schemes and Lisps and it seemed when going through the docs like ECL at that time was going to be a bigger lift to get going.
clang and ECL both seem interesting, as long as LGPL license is ok. They both are complex to embed though - neither are well tuned to be embedded in other applications. (I've been exploring on MacOS). Julia could be interesting too under same questions (and a better license for commercial products) but similarly has a fair bit of glue code needed - especially if you want to restrict (say) filesystem access.
