On 11/15/2010 02:11 PM, Cedric Blancher wrote: > > Why is the debate static-vs-dynamic scoping coming up again? Because before 'typeset' can be standardized in POSIX, we have to get consensus from all the shell implementers that they will agree to implement static scoping. For ksh, the question is moot - ksh93 already does static only. For dash, the question is valid - the current dash implementation is dynamic only, but given that switching to static only could probably be made more efficient, and dash values efficiency, it's a reasonable goal. For bash and zsh, which currently are dynamic only, the problem stems that there are now a number of shell script libraries for these two shells that have exploited dynamic scoping, and which would break if we aren't careful to standardize something that can still allow dynamic scoping as an extension. In other words, this was a probe of the various shell implementers to figure out how easily static scoping can be added on after the fact to a dynamic scoping implementation, so that the shell could conform to a future POSIX revision that mandates static and permits dynamic as an extension. > With this background I doubt any proposal for dynamic scoping will > make it into the next POSIX standard. There's no desire for dynamic scoping in POSIX; David Korn has already made that point clear on the Austin Group mailing list. Rather, there is a desire for minimal effort for complying with a new POSIX requirement of static scoping on shells that currently lack it, as well as backwards compatibility for shells that wish to continue to provide dynamic scoping as an extension to the standard. My take of the Austin Group list discussion is that the next revision of the standard is most likely to have consensus if it just mandates 'typeset' for static scoping, and leaves 'local' as an implementation extension for dynamic scoping. Please, chime in on the Austin Group conversation if you have something useful to add. -- Eric Blake eblake@xxxxxxxxxx +1-801-349-2682 Libvirt virtualization library http://libvirt.org
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