2015-11-15

Defined or undefined?

R7RS doesn't mandate implementations to load a library only once, unlike R6RS. I believe, the reason why is that letting implementators to have variety of options such as without creating/storing library definition anywhere but each time it'd be evaluated. Understandable, just rather inefficient to me. Also it defines the behaviour of multiple import clauses of the same library.

Now, I've got a question. What should happen if there are 2 the same libraries import in the same import clause and one (or more) of the identifier(s) is(are) renamed like this?
(import (scheme base) (rename (only (scheme base) car) (car kar)))

;; are car and kar required to be the same binding?
Honestly, I couldn't read if it's required to be the same in such case from R7RS. Though my guess is the followings:
  • The last paragraph of section 5.6.1 only specifies the case of 2 import clauses importing the same libraries
  • This type of import can't be merged into one import in sense of R7RS import definition (or can it be?)
  • Thus this can be multiple import of the same library.
  • The third last paragraph of section 5.6.1 suggesting the possibility of multiple load when there's multiple import of the same library (can be interpreted as multiple evaluation of library).
The point that I'm not totally sure is that the paragraph which suggest the possibility of multiple load says that this would happen when the library is imported more than one program or library. This would also be interpreted if a library imported twice in the same script or library, then it should only be loaded once. If this interpretation is correct, then above car and kar must be the same bindings. Otherwise, can be different.

Why this matters? Generally, it doesn't. Just wondering if the last case of this Gist is required to print #t by R7RS.

I've also posted this question to comp.lang.scheme: this

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