Hi, all, thanks for the responses. I understand the distinction
between pure functions and impure functions/procedures/IO actions, it
just felt to me in the samples that I quoted that I was in fact
starting from basically the starting point, eventually getting to the
same endpoint (or at least a pair of endpoints that are not easily
distinguished from each other by looking just at code), and inbetween
one path was going through liftIO and the other not. But I guess it
comes down to the fact that, since I'm in a REPL, I'm wallowing in
impurity all the time (or something like that :-) )
regards,
Uwe
On 2/6/08, Bulat Ziganshin
Hello Uwe,
Wednesday, February 6, 2008, 7:44:27 AM, you wrote:
But after that, it sure seems to me as if I've taken data out of the IO monad...
this means that you can't use results of IO actions in pure functions. your code works in some transformed version of IO monad, so you don't escaped it
if we call pure functions as "functions" and non-pure ones as "procedures", the rule is "functions can't call procedures", but all other activity is possible. in your do_action you calls procedure (to format current time) and call a function (to format given time). do_action is procedure (because it works in transformed IO monad), so you don't break any rules
-- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com