Am 12.05.20 um 23:06 schrieb Henning Thielemann:
Thus the type should be:
openFile :: (AlreadyInUseException e, DoesNotExistException e, PermissionException e) => FilePath -> IOMode -> ExceptT e IO Handle
Yes, but then these errors would no longer be exceptions but normal return values (if you remove the ExceptT veneer). So what you say amounts to "exceptions should be removed from Haskell except for programming errors". I agree that communicating IO errors (and similar things) explicitly ie. via return value is the better choice. But the proposal is about Haskell (the language and standard libraries) as it presently is i.e. the one that uses exceptions for IO errors, not the one you want to have and in which IO errors are communicated as return values and openFile would have the type above. And that means your objection to the proposal at hand is irrelevant and beside the point.