[Haskell-beginners] Issue installing reactive-banana-5.0.0.1

[Heinrich Apfelmus]

Miguel Negrao wrote:
> 
> One other question, is it possible in reactive-banana to define
> “recursive” event streams. For instance consider a stream which
> receives numbers between 0.0 and 1.0.  If the last outputted value
> was between 0.8 an 1.0 then output 1-x otherwise output x. After that
> it only leta numbers through if they are between 0.0 and 0.2 or
> between 0.8 and 1.0.

The standard way to do recursion in reactive-banana is to use multiple 
recursion between a  Behavior  and an  Event . See also

   http://stackoverflow.com/a/7852344/403805

Note that the specification you gave does not require recursion, though. 
Here an implementation of your example.

     import Reactive.Banana

     example :: Event t Double -> Event t Double
     example e = filterJust e2
         where
         e2 = f <$> bIsFirst <@> e

         bIsFirst = stepper True $ False <$ e

         between x a b = a < x && x < b

         f True x
             | between x 0.8 1.0 = Just $ 1 - x
             | otherwise         = Just $ x
         f False x
             | between x 0.8 1.0 = Just $ x
             | between x 0.0 0.2 = Just $ x
             | otherwise         = Nothing

Here an example output

     GHCi> interpretModel example [[0.9],[0.3],[0.4]]
     [[9.999999999999998e-2],[],[]]




Best regards,
Heinrich Apfelmus

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