Re: Web development

[Keith Wright]

> From: Sergey Dolin <address@hidden>
> 
> > > > So, maybe someone on this list knows if there is a way to store
> > > > continuations?
> > > You can (best way) use XML. O! It's realy the best way
> > Surely there's nothing to be gained by converting to XML instead of
> > S-expressions?
> I don't know what S-expressions are. Are they  have DTD?

This terminology goes all the way back to 1958 and the Lisp 1.5 system.
Without getting into a big history lesson, just think of S-expression
as meaning Scheme expression and you won't go to far wrong.  It
means a list that is used as a program.

>  XML - is "standard" aproch.

Scheme has a standard too!  They're both just ways of representing
nested lists as character strings.

> > >  But my problems are others:
> > >  i.Guile
> > >  1)I want to return to each http-query  continuation the same user
> > >  has been working before.
> > Why is this a problem?
> I dont know how to store "pointer to current continuatin"... i know it
> is a shame for "real schemer", but i am as i am. 

This a triviality:

  (set! cc (call-with-current-continuation identity))

I do not really know what you two are trying to do and am not
paying much attention, but I very much doubt that "continuations"
(in the Scheme sense) have anything to do with making a transaction
processing system with roll-back.  (At least no more than any
other useful language feature like recursion or arithmetic.)

Calling a Scheme continuation has _no_effect_at_all_
on the values stored in variables.  In particular it does not
roll them back.  If you know C, think of call/cc as a setjmp,
and calling a continuation as longjmp.  It jumps control to
a certain place you have saved, and cuts the stack back 
(or in Scheme's case maybe cuts it forward) so that you have
the right set of local variables to go with the code you jump to,
but the values of those variables are still whatever
was last put into them.

> Actually, I'm going to fix this right away rather than continue with
> my stupid homework about Kant and Carnap and Quine.  ;)

I don't know what your homework is, stupid maybe, but you
better not be bad-mouthing Kant, Carnap, and Quine where
I can catch you!

-- 
     -- Keith Wright  <address@hidden>

Programmer in Chief, Free Computer Shop <http://www.free-comp-shop.com>
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