Comment by armchairhacker

I wish we had something like typed Lua without Lua’s weird quirks (e.g. indexing by 1), designed with performance enhancement and and safety in mind, and with the features you mention.

But like Lua, the base compiler is really small and simple and can be embedded. And it’s “pseudo-interpreted”: ultimately it’s an ahead-of-time language to support things like function declarations after references and proper type checking, but compiling unoptimized is practically instant and you can load new sources at runtime, start a REPL, and do everything else you can with an interpreted language. Now having a simple compiler with all these features may be impossible, so worse-case there is just a simple interpreter, a separate type-checker, and a separate performance-optimized JIT compiler (like Lua and LuaJIT).

Also like Lua and high-level assembly, debugging unoptimized is also really simple and direct. By default, there aren’t optimizations which elide variables, move instructions around, and otherwise clobber the data so the debugger loses information, not even tail-call optimization. Execution is so simple someone will create a reliable record-replay, time-travel debugger which is fast enough you could run it in production, and we can have true in-depth debugging.

Now that i’ve wrote all that I realize this is basically ML. But oCaml still has weird quirks (the object system), SML too honestly, and I doubt their compilers are small and simple enough to be embedded. So maybe a modern ML dialect with a few new features and none of the more confusing things which are in standard ML.