[racket] Engineering Tradeoffs of ANF transforms and the Stateless Server

From: Galler (lzgaller at optonline.net)
Date: Sat Dec 31 20:26:39 EST 2011


While AJAX and client-side continuations enable significant client-side 
computational complexity, I think they complement vs. eliminate the need 
for server-side complexity.

I'm in pursuit of both  (1) server complexity and (2) server-side 

I could achieve (1) by giving up (2), or (2) by forfeiting (1)

and the proximal reason I can't get both right now is I lack a very 
limited dynamic-wind functionality compatible with #lang web-server.


a) I need a redefined dynamic-wind which uses a

a)  call/cc-dynamic-wind to provide the correct prelude-postlude 
behavior when a continuation reified with call/cc-dynamic-wind  is 

c) Its perfectly fine *not* to have this behavior for continuations 
which are reified normally, or exceptions, etc.

I think Friedman's [Friedman and Hayes: Constraining Control] page 17 
implementation should do exactly this.

But, I can't understand why Friedman's code should work. Its over my 
head. And its in scheme84.

There's a much much simpler implementation in the appendix to the 1992 
paper [The Scheme of Things: The June 1992 Meeting], but it still 
confuses me, especially the last five out of six lines of code.

Friedman uses a "rec" form, which seems to be the same as let* (which 
would work with #lang web-server- One clear forbidden construct in #lang 
web-server is a nested set! within a letrec within a define. That will 
not compile.)

Friedman also uses "mapc", which my research has shown is a "for-each"

"thaw" might just be a function application, i.e. (mapc thaw state) -> 
(for-each (lambda (fn) (fn)) state), where state is a list

I'm suspicious that set-car! and set-cdr! work the way one suspects, 

(set-cdr! state new-state)
(set! state new-state)

in Friedman doesn't make much sense to me. Also see last five of six 
lines in the 1992 paper.

If anyone can provide any assistance in helping me to understand or 
implement the Friedman code, I would be grateful.

Criticism of why this plan wouldn't work out is also appreciated.



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