Re: redo-safe-variables and redo-safe-parameters

[Stefan Israelsson Tampe <stefan.itampe@gmail.com>]

> Noha writes
> Hi,

> A few points:

> 1. I really, really think that it is a bad idea for the type of a
> variable to change depending on how it is used (i.e. set!
> vs. set~). That means that you should remove points 12 and 14, and
> maybe some  other points.

I agree with you now, I was a bit too creative there :-)

> 2. You shouldn't specify the semantics in terms of code, but by a 
> description. That means removing points 3, 4, 5, and 7 and replacing
> them with text that says how the variables work. You can move the
> same ideas down to the reference implementation, though - that is
> good.

I will in the end go there meanwhile I like to keep some code for 
clarity.

> 3. I strongly suspect that you will find that MIT Scheme's fluid-let
> has the semantics you want. If it doesn't, I would be interested to
> see an example that shows the difference between that and the type
> of variables that you want.

I think that fluid parameters fluid-let are close in semantics. but I
do not want the backtracking feature of fluid -let in some
applications and it carries an overhead compared to just haveing
variables and an init value.

Note:
I have been going back to guile-log to try to implement the ideas in
actual code. I got it working and implemented in efficient C I
hope. The code for e.g. any-interleave got 8x faster (Now About 10x 
slower
then a simple all in stead of 80). My conclusion now is that to get an
efficient implementation one needs to go back to dynamic-wind
guards. And demand that redo-safeness imply that we assume that the
code backtracks over the dynamic-wind at the state storage point. This
is featurefull enough to satisfy most uses of redo/undo that I can
think of.

/Stefan