[Haskell-cafe] On the purity of Haskell

[Steve Horne]

On 29/12/2011 19:21, Heinrich Apfelmus wrote:
>
> Why would  IO Int  be something special or mysterious? It's an 
> ordinary value like everything else; it's on the same footing as 
> [Char], Maybe Int, Int -> String, Bool, and so on. I see no difference 
> between the list  [1,2,3] :: [Int]  and the action  "pick a random 
> number between 1 and 6" :: IO Int  .
>
Because performing the action (as part of extracting the result out of 
it) is relevant to the semantics of the language too, whether an IO 
monadic random generator or an an interaction with the user via a GUI or 
whatever.

BTW - why use an IO action for random number generation? There's a 
perfectly good pure generator. It's probably handy to treat it 
monadically to sequence the generator state/seed/whatever but random 
number generation can be completely pure.