[throwaway894345]

Typically getting languages to talk with each other is very difficult and onerous for the programmer unless the languages were built to interface with each other, and in this case, that probably means "different syntax frontends for a common semantic backend".

Even if you build Python-like and JS-like and etc syntax frontends for a hypothetical common backend, they will only be syntactically similar, but the semantics and standard libraries will be different than Python, JS, etc so there's really very little to be gained here.

And maybe it's even worse, since the whole goal is to allow a Python-like frontend to reference functions and variables defined by other frontends, the authors will probably have to understand certain aspects of all frontends. if those frontends are sufficiently similar and familiar (e.g., Python and JS) then there isn't much of a problem, but if you throw in an obscure syntax like Nix this becomes harder.

[yjftsjthsd-h]

I'm not saying that I want library/module integration; I want nix to be able to build a package by creating a working directory with a set of input directories and an output directory, and then running an arbitrary script to convert the inputs into the output.

[throwaway894345]

If I understand correctly you can do that today (nix builds with bash scripts by convention but there's no reason you can't ask it to use Python or whatever or call into Python/etc from bash). But that's all orthogonal to the expression language.