Proposal: Add Text.Read.maybeRead :: Read a => String -> Maybe a

[John Meacham]

On Fri, Feb 08, 2008 at 11:39:18AM +0100, Henning Thielemann wrote:
> > say that next time you get a mysterious "fromJust: Nothing" error with
> > no context, error messages in haskell are quite an issue as is, _any_
> > useful information is good, passing them on to the user without
> > interpretation is loads better than not having any clue what went wrong.
> 
> Since 'error' denotes a programming error, not an exception, there is no
> need that the user understands the error message. It is entirely the task
> of the programmer to understand the message or its absence and it would
> be completely ok if the program aborts with "the programmer made a
> mistake, please complain to him".
>  http://www.haskell.org/haskellwiki/Error
>  http://www.haskell.org/haskellwiki/Exception

I am not sure what distinction you are making between the user and the
developer. I don't believe errors should be catchable at all and find
the ability to catch 'error' rather unaethetic. But I do believe they
should be absolutely as informative as possible in order to track down
bugs and the string argument is invaluable for that. I am not saying
that "users" will be happier seeing "readM: no parse" than "fromJust:
Nothing" as they both indicate bugs in your code, but getting a bug
report with the first is much more useful and more precise. Haskell is
hard enough to debug as is, we should take help wherever we can get it.

        John


-- 
John Meacham - ⑆repetae.net⑆john⑈