Just to be clear, I'm using the word "module" here in an extremely generic, language independent way. Basically in the sense of "things that can be compiled individually". In many languages (for example in Lisp), those are functions. A syntactic loop construct ordinarily can't even cross a function boundary.

If your language of choice features formalized modules in the Modula-2 sense, its loops most likely can't span multiple functions even within a single Modula-2-sense module, even if you wanted that (for example, in a state machine with named states as functions which tail-call each other to switch state by transferring control, or something like that).

Why is that unreasonable? I might be missing something (I have no formal CS education), but I can imagine it, e.g. a base graph datastructure library, and then two libraries dependent on the base library being used together for some graph traversal work (where callbacks are used).