[R6RS] modules

[R. Kent Dybvig]

> How many times is the body of M evaluated? Is it just once, so that all
> of the calls to `get-x' in N and P call the same function? ...

Again, I prefer just once.

> ... If so, what
> mechanism allows the result to be treated differently in N and P?

Here's one approach:

* (require M) introduces a substitution marked "run-time" from each
  import name to the corresponding export label.

* (require only-for-syntax M) introduces a substitution marked
  "expand-time" from each import name to the corresponding export label.

* (require also-for-syntax M) introduces a substitution marked
  "any-time" from each import name to the corresponding export label.

When expanding transformer code, the expander signals an error
for attempted references through substitutions marked "run-time";
otherwise, the expander signals an error for attempted references through
substitutions marked "expand-time".

Kent