[Haskell-cafe] Decorating exceptions with backtrace information

[Ben Franksen]

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.