[Haskell-cafe] On the purity of Haskell

[Artyom Kazak]

Gregg Reynolds <dev at mobileink.com> писал(а) в своём письме Fri, 30 Dec  
2011 17:23:20 +0200:

> Regarding side-effects, they can be (informally) defined pretty simply:   
> any non-computational effect caused by a computation is a side-effect.

I wonder: can writing to memory be called a “computational effect”? If  
yes, then every computation is impure. If no, then what’s the difference  
between memory and hard drive?

By the way, the Data.HashTable is in IO monad. Is it impure? Would it be  
pure if designers had chosen to use ST instead?