Remacs is developing some nice Rusty idioms for elisp primitives. Here's vectorp: https://github.com/Wilfred/remacs/pull/212/files
miniblog.
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Fun post on implementing a JIT for elisp, with a great introduction to calling conventions on elisp primitives: https://tromey.com/blog/?p=999
Firefox is shipping formally verified crypto primitives!
Defining a lisp with 6 primitives is neat, but it's not enough to be general purpose. No I/O. Are there minimalist PLs that are usable?