[Haskell-cafe] Question: Lazy Incremental Evaluation and Haskell?

David Barbour dmbarbour at gmail.com
Fri Oct 7 08:34:22 CEST 2011

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

On Thu, Oct 6, 2011 at 2:55 PM, Benjamin Redelings I <
benjamin.redelings at 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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