> How much harder would it be to implement than say, JS? 3 orders of magnitude more difficult?
We can look at the size of the GCC frontends for various languages to get some idea of the complexity compared to other languages:
gcc/ada/*.ad* : 712194 lines (excludes C files and gcc-interface folder)
gcc/ada/libgnat/ : 438117 lines (standard library)
gcc/ada/libgnarl/ : 61705 lines (runtime)
gcc/c/ : 63816 lines
gcc/cp/ : 279732 lines
gcc/c-family/ : 53110 lines
gcc/d/ : 212457 lines (185253 are DMD)
This probably isn't the best metric, and I may be missing some files as I'm not very familiar with GCC internals, but if I'm getting this right then we can see that just the Ada frontend has more lines than the C, C++, and D frontends combined.
> I wonder if there's a deno/bun style business in here.
You could do this with a library without anything special in Ada. You don't need to dig deep in to the internals like you do with JS.