[Haskell-cafe] Question on a common pattern

Donn Cave donn at avvanta.com
Tue Mar 15 16:11:15 CET 2011

Quoth Achim Schneider <barsoap at web.de>,
> I use 
>     someIO >>= f where
>       f Opt1 = ...
> If it's a common pattern, you can even do
> opts f _ _ (Opt1 x) = f x
> opts _ g _ (Opt2 x) = g x
> opts _ _ h (Opt3 x) = h x
> . Functions are easier to mess around with than case expressions.

I like this ... or, I would like it, if I could make it work!

I get "The last statement in a 'do' construct must be an expression",
if I don't drag the `where' clause down to the end of the `do' block
around `someIO', which of course is what we're trying to avoid with
the case expression.  I must have missed a trick with the layout?

	Donn Cave, donn at avvanta.com

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