[Haskell-cafe] Practical Haskell question.
lemming at henning-thielemann.de
Mon Jun 25 04:58:16 EDT 2007
On Mon, 25 Jun 2007, Tomasz Zielonka wrote:
> On Mon, Jun 25, 2007 at 10:29:14AM +0200, Henning Thielemann wrote:
> > Imagine all performActions contain their checks somehow. Let
> > performActionB take an argument.
> > > do
> > > x <- performActionA
> > > y <- performActionB x
> > > z <- performActionC
> > > return $ calculateStuff x y z
> > Now performActionB and its included check depend on x. That is, the check
> > relies formally on the result of performActionA and thus check B must be
> > performed after performActionA.
> IIUC, this limitation of Monads was one of the reasons why John Hughes
> introduced the new Arrow abstraction.
How would this problem be solved using Arrows?
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