Ah! It seems that my wording was ambiguous. All I was trying to say is that
there is nothing you can do with an IO action which will cause an otherwise
pure expression to exhibit side effects during evaluation, *not* that an IO
action is observable in pure code or that they are arbitrarily manipulable.
On Aug 8, 2013 9:39 AM, "Jerzy Karczmarczuk"
I am sorry for having mixed-up arguments (but who throws the first stone?...)
Jerzy seemed to suggest that the "impurity" of IO was somehow related to it not supporting very many operations.
No, not really. I added
First, it is not true that you can do with, say, (printStr "Ho!" ) whatever you want. In fact, you can do almost nothing with it. You can transport it "as such", and you can use it as the argument of (>>=).
after the message of Jake McA.
*You can do whatever you want with them* with no harmful effects in any Haskell expression.
This was an additional layer of bikeshedding, not exactly about purity. Or, just a bit: the ONLY "real" operation on an action, i.e. (>>=) produces side-effects... Other don't, but --
Again, here my point is that calling "pure" an entity which is opaque and inert, is meaningless (or "redundant" if you wish...), this was all.
Jerzy K.
PS. Tom Ellis:
One could simply implement IO as a free monad
Interesting. I wonder how.
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