Am Mo., 11. Feb. 2019 um 10:43 Uhr schrieb Alex Shinn <xxxxxx@gmail.com>:

[...]

> Without spending much time thinking about this originally I didn't consider it even possible in portable R7RS small, but I realize we could bind these to unique objects and key on those instead of the identifiers.
>
> If we really want this it would be a significant deviation, requiring changes to the spec and implementation, so would have to be a new SRFI.  I might take this up if there were serious interest from R7RS large.

[...]

I would volunteer to write a SRFI about the environment monad (which
may be of independent interest as well) and whose implementation can
then be used as a basis for SRFI 159 (thanks to the modular
implementation of SRFI 159 this is easy to achieve).

How are `local′ and `local!′ (or `with′ and `with!′, respectively)
supposed to interact? There are four possibilities:

(1) `local′ conceptually creates a new scope. All changes introduced
by `local!′ inside this scope are revoked when the `local′ scope is
left.
(2) Only changes by `local!′ to variables introduced by `local′ are
revoked when the `local′ scope is left.
(3) Changes by `local!′ always persist, even across `local′ scopes.
(4) It's up to the implementation.

(chibi monad environment) currently implements (2).

-- Marc