Readline read_history and write_history addition

[Simon Marlow]

Judah Jacobson wrote:
> On Mon, Feb 4, 2008 at 6:06 AM, Yitzchak Gale <gale at sefer.org> wrote:
>> Simon Marlow wrote:
>>  > However, I do agree that exceptions should generally be used for
>>  > exceptional conditions, rather than for general control-flow.  This is an
>>  > example of a *good* reason to avoid an exception: because to use an
>>  > exception for a non-exceptional condition is poor style.
>>
>>  That is also my opinion. Some people have disagreed.
>>  So this should be the focus of the decision then.
> 
> I also agree that exceptions should only be used for exceptional
> conditions; but I do think that this is one of those situations.  I'll
> try to explain why below.  (Thanks, Yitzchak, for forking off the
> thread about fixing limitations of MonadIO.)
> 
> I assume that the following conditions are already considered
> exceptional (I haven't ever heard anyone complain that they throw an
> exception):
> - readFile : read a nonexistent file
> - writeFile : write to a file in a nonexistent directory
> - getEnv: retrieve an unset environmental variable

FWIW, this was hotly debated at the time, and I do believe we made the 
wrong decision w.r.t. getEnv, mainly because I always end up writing "try $ 
getEnv", or I forget the try and have to fix the bug later.

Cheers,
	Simon