I see the problem now.  But I am confused as to why there are no Bool class (like Num, Fractional...) in Haskell.   If I had such a class then the problem is solved, (by making the "pm a" an instance of it) right?  Or are there still more issues that I am not seeing?

thanks,

daryoush

On Mon, Feb 28, 2011 at 7:34 AM, Chung-chieh Shan <ccshan@cs.rutgers.edu> wrote:
Daryoush Mehrtash <dmehrtash@gmail.com> wrote in haskell-cafe:
> I am confused about this comment:
> > Mostly we preferred (as do the domain experts we target) to write
> > probabilistic models in direct style rather than monadic
>
> In the haskell implementation of the lawn model there are two different
> version of the grassModel (
> https://github.com/rst76/probability/blob/master/src/Lawn.hs)...
> By domain expert preferring direct style do you mean that they prefer
> the first version over the 2nd version?

No, there is no way to write probabilistic models in direct style in
Haskell, and domain experts prefer neither Haskell version you showed.

A symptom of direct style is being able to write something like

   flip 0.3 && flip 0.5

where (&&) takes two Bool arguments.

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