23 Jan
2010
23 Jan
'10
11:39 p.m.
Adrian Adshead wrote:
1) Is it possible to have a function with an IO Action as an input parameter (and not just ignore the parameter) and have a non-IO return value? (ie is f :: IO a -> b possible without ignoring the IO a)
pretty much no, but consider, we can return a data structure constructed out of those IOs, without actually learning anything about what actions they are intended to do. For example: f :: IO a -> [IO a] f io = iterate (\io2 -> (io2 >> io2)) io returns a list, in which the first action would do the IO once, the second would do it twice, the third element would do it four times, the fourth element, eight times, and so forth. Obviously, it is only occasionally useful to do something strange like that. -Isaac