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Apologies, this is a cross post from 'R-devel', where I sent this message a few
months ago when I did not realize there was an 'r-package-devel' list. So here
it is again in the correct list:
I'm working on a package that implements a REPL. A typical interaction with
the package might look like:
> launch_REPL()REPL> 1 + 1[1] 2REPL> QDo you wish to save results? [y/n]REPL>
> ygoodbye ...>
This is very similar to what happens when in `browser()`: the REPL evaluates
arbitrary R user expressions and offers some additional commands.
In order to implement functionality required for the REPL I must trace some
functions in the base package. The trace is removed `on.exit()` from the REPL,
so the functions are only modified while the `launch_REPL` function is
evaluating. Unfortunately this is against the letter of the law (as per CRAN
policy):
> A package must not tamper with the code already loaded into R: anyattempt to
> change code in the standard and recommended packages whichship with R is
> prohibited.
Is there any chance that this very limited (only during my function evaluation)
modification of base functions with `trace` could be considered to meet the
spirit of the law, if not the letter? Package users would be duly notified
this is happening.
Alternatively, if this is not allowed, would it be acceptable to ship the
functionality turned off by default with a user option to enable it (documented
with warnings about how this is non-standard behavior, etc.)?
Regards,
Brodie Gaslam.
PS: More details for those who care: the REPL among other things implements an
environment that has for parent `as.environment(2)` so that objects in the
global environment are not visible while in the REPL, but otherwise the full
search path is. Anytime the search path changes I need to update the REPL
environment to re-point to `as.environment(2)`, which means I need to know when
the search path changes. I do this by tracing `library`/`attach`/`detach` and
triggering a side effect that updates the REPL environment parent any time
those are called. The search path itself is untouched. I cannot just parse
user expressions searching for those functions as the user can use any
arbitrary expressions, including sourcing files that contain the `library`,
etc. calls.
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