On 21 Feb 2009, at 01:30, Patrick LeBoutillier wrote:
Hi all,
I'm trying to implement the following simple Perl program in Haskell:
my $nb_tests = 0 ;
sub ok { my $bool = shift ; $nb_tests++ ; print STDOUT ($bool ? "ok" : "nok") . " $nb_tests\n" ; }
ok(0) ; ok(1) ;
The output is:
nok 1 ok 2
I'm pretty much a Haskell newbie, but I know a bit about monads (and have been reading "Real World Haskell"), and I think I need to put the ok function must live inside some kind of state monad. My problem is that I also would like the ok function to perform some IO (as shown above, print).
How is a case like this handled? Can my function live in 2 monads?
I personally wouldn't use two monads at all for this – in fact, I'd only use IO in one function: main = putStr . unlines . results inputs . snd . tests $ inputs inputs = [1,2] tests = foldr (\_ (x,l) -> (not x, x:l)) (True,[]) results = zipWith result result testN True = "ok " ++ show testN result testN False = "nok " ++ show testN Bob