[Haskell-beginners] State as function?

Daniel Trstenjak daniel.trstenjak at gmail.com
Sun Apr 6 14:05:14 UTC 2014

Hi Martin,

On Sun, Apr 06, 2014 at 03:20:14PM +0200, martin wrote:
> I started out with assoc lists and hashmaps. However, I found it
> diffiult to ensure that all 6 GuitarString have a something attached
> and found myself messing with Maybes. In the real world, there is no
> way a GuitarString can have "no state at all", while the HashMap
> approach would provide this option.

I would start by designing the data structures that represent your
possible states. That way you can also ensure that there can't be
any non representable states.

I really don't now what makes sense in your case, but something like:

data StringState = Resting
                 | Oscillating

data Guitar = Guitar
   { string1 :: StringState
   , string2 :: StringState

If you have worked out the right data structures, then writing
the surrounding code can become quite naturally.


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