Constructed docstrings for closures

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

When converting backquoted lambdas to closures, I've often bumped into
the following problem:

   `(lambda (foo bar)
      ,(concat "Toto is very " blabla ".")
      (code using foo and bar (and ',blabla as well)))

So code-wise, this can be replaced by a closure just fine, but doc-wise
we don't have a way to construct a different docstring for
every closure.

I'd like to lift this restriction by offering a new feature that lets us
do something like:

   (lambda (foo bar)
     <something-magical-here>
     (code using foo and bar (and blabla as well)))

and get the closure we want with the docstring we want.

Does anyone have an idea of what the <something-magical-here>
could/should be?


        Stefan