[Haskell-cafe] <|> that short-circuits in IO ?

[Kim-Ee Yeoh]

On Thu, Oct 30, 2014 at 8:50 PM, Roman Cheplyaka <roma at ro-che.info> wrote:

> >> liftA2 (<|>) b a
> >
> > B
> > A
> > Right 42
> >
> > (In the latter case I don't want A in the output…)
>
> Wrap it into ExceptT (from the latest transformers), as in
>
>   runExceptT $ ExceptT a <|> ExceptT b


With the latest transformers, I still get

B
A
Right 42

i.e. the A hasn't been eliminated.

What am I missing?

-- Kim-Ee
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