Hi Michael,
On 25 Jun 2007, at 06:39, Michael T. Richter wrote:
do
x <- performActionA
y <- performActionB
z <- performActionC
return $ calculateStuff x y z
I don't know about you're exact example, but here's what I'd do.
Control.Monad has functions like when, unless, and guard that you can
use to check whether the "precondition" holds. I find an "ifM"
combinator quite useful sometimes:
ifM :: Monad m => m Bool -> m a -> m a -> ma
ifM cond thenBranch elseBranch = do
b <- cond
if cond
then thenBranch
else elseBranch
If everything checks out, you can then execute your A, B, and C actions.
I don't think you really want arrows here. The right idiom is
applicative functors (see Control.Applicative). You could then write
the above as:
calculateStuff <$> x <*> y <*> z
Hope this helps,
Wouter
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