[Haskell-cafe] Identity of indiscernibles

Jerzy Karczmarczuk jerzy.karczmarczuk at unicaen.fr
Thu Aug 8 15:38:41 CEST 2013

I am sorry for having mixed-up arguments (but who throws the first 

> 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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