On Feb 16, 2006, at 7:32 PM, John Meacham wrote:
...
Again that doesn't compile, because "when" requires a ()-returning monad as its second parameter, but the "string" parser returns "String". Same thing with if-then-else, when used to switch IO actions and such: the IO actions must fully match in type, even if the returned value will be discarded, and again that can be trivially resolved by adding the "return ()".
This is a straight up bug in the definition of when I hope we fix. it should have type
when :: Bool -> IO a -> IO () when = ...
Arguably this could be made true of *every* function which presently takes m () as an argument. That is, we could systematically go through the libraries and convert every function of type: f :: (Monad m) => .... -> m () -> ... into f :: (Monad m) => .... -> m otherwiseUnusedTypeVariable -> ... This would basically eliminate the need for "ignore". I can see taste arguments in either direction, but really the language ought to pick an alternative and use it everywhere (including for >>). -Jan-Willem Maessen
John
-- John Meacham - ⑆repetae.net⑆john⑈ _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe