On Wednesday, March 27, 2013 11:29:39 AM Noah Lavine wrote: > On Wed, Mar 27, 2013 at 11:04 AM, Stefan Israelsson Tampe < > > stefan.ita...@gmail.com> wrote: > > Hi Noha, > > > > On Wed, Mar 27, 2013 at 3:29 PM, Noah Lavine > > <noah.b.lav...@gmail.com>> > > wrote: > > > Hello, > > > > > > > > > On Wed, Mar 27, 2013 at 9:22 AM, Stefan Israelsson Tampe > > > > > <stefan.ita...@gmail.com> wrote: > > I don't understand the difference. If I use ~, I get redo-safe > > behavior, and > > > > > if I use !, I get regular behavior (value shared between dynamic > > > states). Can I use ~ and ! on the same variable at different > > > places in the code?> > > If > > > > > yes, doesn't it have to switch behavior? > > > > using set! means that you basically destroys the redo safe property. > > There is no sound concept where you mix them. If you want to mix > > them > > use ~ and add correct function guards to describe the semantics. > > ... > > You want to allow a user to let one variable behave as with set! and > one as > > with > > set~. It is not broken, the useres sees ~ on one of the varibles and > > ! on the other. > > Yes, I agree. What I'm saying is, there should be two different ways > to declare the variables, and once a variable is declared, you should > not need to look elsewhere in the code to see whether it acts like a > regular or redo-safe variable. If that is what you specified, I > apologize, but I thought that it wasn't. Hmm, your really are right in the sense that the common ideom in computer language design is to type a variable at the declaration of the variable. So basically a user would then do something like (for ((~ i) from 0) code ...) to force the intruduction of a redo safe variable. Hmm yolly good. This might be the better semantic and not trust so much on some magic. I would still require (set~ i 1) and (~ i) for these variables? With this approach you might want to consider to change with-redo-varibles e.g.
(with-redo-variables (((~ a) 1)) code ...) to guard it in a redo safe manner and then (with-redo-variables ((a 1)) code ...) as a normal variable and beeing a noop. Error checking can be done via macros so now everything can be made ontop on a rich syntax system and r5rs. Does this sounds like as a better approach? > In particular, I think that having an MIT-Scheme-style fluid-let will > do the right thing here. I would be interested in talking about its > interaction with closure variables, but I think that it's the right > thing here with regard to continuations and mutable state. > > > BTW. srfi's shouuld be careful about specifying dynamic state in > > order to achieve thread safe concpets, Scheme48 is threadsafe with > > their fluid-let, guile would not be. > > Yes, that's an interesting point. I think that I will rewrite the specification with the help of the assumption of the pressense of parameters srfi. I think that is smart. /Stefan
