minh thu wrote: /about the stream algorithms, lazy style/
can you know a mean to express such computation but with elements depending of time (in about the same way as languages as esterel) (i.e. depending of IO)? Paul Hudak uses a Channel in his book Haskell SOE .. but is there another way ?
Frankly, I don't see it well. The co-recursive, lazy constructions are based on the fact that it is the consumer who unrolls the list and forces the reduction. So, the unevaluated closures should contain somehow the latent data, or rather refer to them. Synchronous processing is another story, here the producer is really active. Esterel until the version 4 demanded that all 'circuits' which handled the data flows be *acyclic*; now it is more flexible, so you can do a lot of "own-tail-eating snakes" with it, but differently. I believe that ways of producing intricate streams by such languages or Lustre are somehow based on continuation mechanisms. The paper on Esterel, etc. : ftp://ftp-sop.inria.fr/esterel/pub/papers/foundations.pdf gives you an example in Lustre X[n+1] = U[n+1]*sin(X[n] + S[n+1]-S[n]) S[n+1] = cos(S[n]+U[n+1] in a form remarkably analogous as I did: node Control(U:float) returns X:float var S:float let X = 0.0 -> (U*sin(pre(X)+S-pre(S)); S = 1.0 -> cos(pre(S)+U); tel So, I would say that this is obviously a live domain. The language Signal can oversample, and produce output "faster" than the input, but I have never followed the details. Perhaps some YamPa-ladins who read this list could shed some light on the reactive stream processing? They use Arrows, a generalization (and twist, not compatible) of Monads, so there is obviously *some* relation to continuations here... But I am a Perfect Non-Specialist. Jerzy Karczmarczuk