Functional Reactive Programming can model this sort of 'change over time' incremental computation, but I doubt you'd get a performance benefit from it unless your operations are considerably more expensive than '+' on numbers. Look into the 'Reactive' library, and Conal Elliott's paper on it (Push-Pull FRP). On Thu, Oct 6, 2011 at 2:55 PM, Benjamin Redelings I < benjamin.redelings@duke.edu> wrote:
Hi all,
I'm not sure this is the right forum for this question. If so, please let me know where else might be more appropriate. My question is, roughly, is there already an existing framework for incremental evaluation in Haskell? That is, if I write a program using Haskell, and then change a small part of this program, can the modified program re-use any results which are calculated by the first, unmodified program? This would be really useful for CPU-intensive statistical software and other scientific computing.
For example, if I have the expression (x+y)+z, where x=1, y=2, and z=4, then I need not recalculate (x+y) when z changes. However, (x+y)+z must still be recalculated. This is useful in speeding up statistical software that optimizes a complex function of many arguments, when only one argument changes at a time. It is also useful for Markov chain Monte Carlo (MCMC) since usually one changes only one argument at a time there as well.
I haven't seen much work on this using the lambda calculus for this since JH Field's Ph.D. Thesis "Incremental Reduction in the Lambda Calculus". There are a number of programs that represent the calculation as a static DAG (directed, acyclic graph), but this can't handle functions very well. I'm currently trying to write an interpreter that could do this correctly, but I don't want to reinvent the wheel. Can anyone point me to where I could find more information about how to do this in a Haskell framework?
thanks! -BenRI -- Benjamin Redelings
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