Re: Mathematica scoping / contexts / variable localization

*To*: mathgroup at smc.vnet.net*Subject*: [mg105061] Re: [mg105023] Mathematica scoping / contexts / variable localization*From*: Leonid Shifrin <lshifr at gmail.com>*Date*: Thu, 19 Nov 2009 05:25:13 -0500 (EST)*References*: <200911181158.GAA04246@smc.vnet.net>

Hi Leo, I certainly don't qualify as a guru (and don't want to), but here are my two cents. 1. I usually think of a notebook as an interactive development and visualization tool (apart from it being an interactive document, the aspect which is more relevant for presentation rather than for development), something like a top-level in some other functional languages. Modules and other smaller-scale localization tools should be sufficient within a notebook, and if they are not, it's a clear sign to me that the (part of the) functionality must be moved into a properly formed package (at least using BeginPackage - EndPackage etc). 2. Nobody forbids you to use BeginPackage - EndPackage with inner Begin-End and private sub-contexts within a notebook, with the same benefits as they give you in stand-alone package files. 3. A somewhat related question about automation of the steps needed to localize some code in a certain context was recently asked on the group. I posted some possible solution in this thread: http://forums.wolfram.com/mathgroup/archive/2009/Aug/msg00701.html It is not without bugs though - I mentioned some of the limitations (all of which can be fixed) in my post. Eventually I will fix them and have a more complete solution available. See if the solution from my post can serve your needs. Regards, Leonid On Wed, Nov 18, 2009 at 2:58 PM, Leo Alekseyev <dnquark at gmail.com> wrote: > Dear Mathematica gurus, > > One of the things that initially made Mathematica difficult for me to > use was scoping -- in particular, the fact that all symbols by default > appear in the global namespace. Even though this is a default > behavior for interactive evaluation in many packages, e.g. > R, in Mathematica, it leads to a greater potential for errors because > unlike those languages, in Mathematica > (1). a symbol can have multiple DownValues, and > (2). if one forgets to explicitly localize a symbol inside a scoping > construct, it may silently be taken from the global namespace. > > After many years I finally figured out a (more or less) clean way to > structure my code and workflow, through a combination of defining > modules, contexts, packages, and careful use of Clear and Remove. > > I still wonder, however, why there isn't a construct similar to Module > that would define a unique private context for _all_ symbols within > the construct (i.e. without having to declare them in a list). You > can kind of simulate this behavior by using BeginContext["MyCont`"] > together with redefining $ContextPath temporarily to only have > "MyCont`" and "System`". This is obviously too verbose to be of > practical use, but I do wonder why there isn't a built-in construct. > > I suppose my question is -- is there a deep wisdom behind its absence, > or perhaps I am an anomaly in thinking that such behavior (automatic > lexical scoping for symbols in subroutines, present in R and > many others) would be incredibly handy?.. > > Thanks, > --Leo > >

**References**:**Mathematica scoping / contexts / variable localization***From:*Leo Alekseyev <dnquark@gmail.com>