[Haskell-cafe] Converting IO [XmlTree] to [XmlTree]

Cristiano Paris frodo at theshire.org
Tue Apr 14 11:50:03 EDT 2009

On Tue, Apr 14, 2009 at 5:42 PM, Luke Palmer <lrpalmer at gmail.com> wrote:
> ...
> However, the way I see it is that unsafePerformIO *is* evil by itself, and
> it is only by the addition of Holy Water that it is benign to use.

That's what I meant but your words are indeed more effective :)

> Ryan Ingram described it as a way to achieve "RTS extensions", which I think
> is a fine way to put it   I consider Debug.Trace to be an instance of this:
> we are extending the RTS to provide execution traces.
> I guess it's a teaching style thing.  Mostly, if someone sees "I have an IO
> [XmlTree] and I need an [XmlTree]", I want the "I'm asking the wrong
> question" synapse path to fire, rather than the "just use unsafePerformIO"
> one.

Yes, I think your analysis is correct. Perhaps I was a bit too dry in
my original answer.


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