Bob Ippolito, thank you for great explanation! Your suggestion is working.
Marcin Mrotek, thank you for additional info.
On Sat, Jul 11, 2015 at 9:09 PM, Marcin Mrotek
Hello,
Does this mean that they do not perform IO, or do IO but "break out of" / hide their IO using unsafe or something?
No, monad transformers sort of compose "backwards", that is, if you have something like FooT (BarT (IO a)) then after running everything, you'll get something in the lines of IO (Bar (Foo a)). That's why IO, if it is there at all, must be at the bottom of the stack.
Now, I don't know the library you're using, from the docs it would appear that you indeed can runInstagramT without any IO in there, but some of the actions defined force this or that constraint, and in particular this "getUserAccessTokenURL2" forces (MonadControlBase IO m), which is more or less a fancy way of saying that there must be IO at the bottom.
Best regards, Marcin Mrotek _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners