[Haskell-cafe] How to build a generic spreadsheet?
sebastian.sylvan at gmail.com
Fri Feb 23 18:00:54 EST 2007
On 2/23/07, Sebastian Sylvan <sebastian.sylvan at gmail.com> wrote:
> On 2/23/07, Greg Fitzgerald <garious at gmail.com> wrote:
> > I want to write a program where a user would update a bunch of variables,
> > and everything that depends on those variables (and nothing else) are
> > recalculated. Basically, a spreadsheet, but generalized for any
> > computation. Could someone recommend an elegant way to do it or some good
> > reading material?
> Off the top of my head, one cool way of doing it would be to have each
> variable be a separate thread (they're lightweight, so it's okay!
> :-)), and you would have a list of input connections and output
> connections, in the form of TVars.
> In its resting state you would have a transaction which simply reads
> all of the input variables, and returns the new list of inputs if and
> only if either of them are changed, something like:
> -- not compiled, consider it pseudocode :-)
> getInputs :: (Eq a ) => [( a, TVar a)] -> STM [a]
> getInputs inp = do
> let (vals, vars) = unzip inp
> newVals <- mapM readTVar vars
> when ( newVals /= vals ) retry -- at least one input must've been changed
Bah, this should be:
when ( newVals == vals ) retry
More information about the Haskell-Cafe