I like Lua, but after going all in on Gambit-C^1 for a bit, I'm not sure anything can top its level of integration. Besides compiling to C, it just lets you straight up write C inside of a .scm file.
(c-declare #<<c-declare-end
#include <stdio.h>
c-declare-end)
((c-lambda () void
#<<c-lambda-end
printf("Hello World!\n");
c-lambda-end))
and then run the corresponding executable
gsc -exe embed.scm && ./embed
1.
https://www.deusinmachina.net/p/gambit-c-scheme-and-c-a-matc...