[Haskell-cafe] Re: Difference between div and /

Henning Thielemann schlepptop at henning-thielemann.de
Wed Jun 2 10:11:27 EDT 2010

Sorry, I missed this post.

Maciej Piechotka schrieb:

> Well - i tried to write some package dealing with distributions etc. 
> If you have something like that:
> instance ... => Distribution (Linear a) a where
>     rand (Linear f s) g =
>         let (gf, gt) = genRange g
>             (v, g') = next g
>         in (g', f + (fromIntegral v * s) / fromIntegral (gt - gf))
> (I haven't check it but IMHO it is right implementation)
> Now I have following options:
>  - Implement per Int/Int8/...
>  - Implement IntegerLinear and FractionalLinear separatly

That is, what you need is a general division with rounding. But you
might more generally want a custom type class with a method that selects
an element from a set for given parameters gf, gt, v. This way, you
could also handle distributions on Enumeration types. You certainly you
do not want, say a division operation on Monday, Tuesday, ..., Sunday,
but having a probability distribution of weekdays is very reasonable.

Btw. you may want to have a look at:

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