setenv and let-binding process-environment

[Michael Heerdegen]

Hello,

I've fallen into a trap.  I had expected that (something like)

(progn
  (setenv "A" "1")
  (let ((process-environment process-environment))
    (setenv "A" "2"))
  (getenv "A"))

would return "1", but it returns "2".  A similar expression and the
false assumption about it's semantics introduced a weird issue in my
code.

But I think others could come to the same conclusion that I came to
after reading the docs (e.g. setenv doc: "This function works by
modifying ‘process-environment’").

Should we document that case, or change the behavior, or do I miss
something?


BTW, after having located the cause of the trouble, I changed the code
to use

  (let ((process-environment (cons additional-binding process-environment)))
    { start the process })

following an advice in the manual.  That works without problems.


Thanks,

Michael.