[plt-scheme] On PLaneT packages and compatible upgrades

100%. -- Matthias


On May 10, 2006, at 8:27 AM, Matthew Flatt wrote:

> At Wed, 10 May 2006 07:58:01 -0400, Matthias Felleisen wrote:
>> I would very much prefer a tool -- "Compatible Extension" -- that
>> consumes two modules and either says "yes" or lists the things that 
>> one
>> module exports and the other doesn't. In addition, it should come with
>> an option "Generate Adapter," which produces a module m- with the same
>> interface as m.v0 but with values from m.v1. (This should be N+2 
>> lines:
>> module, import plus one export per m.v0 interface.)
>
> This took me a while to understand. I'll repeat it back just to see if
> I do understand:
>
>  1. Adding exports is not a compatible upgrade.
>
>  2. Suppose the only change between version N.M and (N+1).0 is bug
>     fixes plus new exports. In that case, it's trivial to implement
>     version N.(M+1) in a way that captures future bug fixes in the
>     (N+1).* series: import (N+1).*, then re-export everything that was
>     exported from version N.M.
>
>  3. Since the implementation of N.(M+1) is trivial given N.M and
>     (N+1).0, it would be nice to have a tool that does it for you.
>
>  4. Also, library implementors should also use a tool to double-check
>     that any implementation K.(J+1) is a compatible extension of K.J
>     (i.e., it has the same exports).
>
> Is that right? If so, I like it.
>
> Matthew
>