[Haskell-cafe] Re: Practical Haskell question.

[apfelmus]

Michael T. Richter wrote:
> It looked to me like there were people arguing about whether the "x"
> returned from one action was going to be used in the next action.
>
> Let me try and rephrase the question.  :)
>
> [rephrase]

Yes, and that's an important constellation your problem description does
not consider. Take the code

 doStuff():
     if checkPossible( ?? ):
         x <- A
         if x
           then B
           else C
     else:
         exception "Preconditions not met"

What should be put as argument into checkPossible? checkPossible([opA,
opB, opC])? What if x happens to be always true and C is never run? What
if B is possible if and only if C is not?

Sequencing actions is not just putting them in a row, but also feeding
the results of one action to the next ones. You have to restrict this in
some way to make your goal possible.

> And can it be done somehow in Haskell?

Most likely, and Haskell even tells you when your approach doesn't work
without further specification :)

Regards,
apfelmus