[Haskell-cafe] Splitting off many/some from Alternative

[Gregory Crosswhite]

On Dec 14, 2011, at 8:38 AM, Thomas Schilling wrote:

> On 12 December 2011 22:39, Antoine Latter <aslatter at gmail.com> wrote:
>> But now they look as if they are of equal importance with the other
>> class methods, which is not really true.
> 
> Maybe, but something like this is best fixed by improving
> documentation, not by shuffling things around and needlessly breaking
> APIs.  I also agree that if an Alternative instance doesn't make sense
> it should be removed.   The current documentation is indeed very terse
> indeed.  In particular it needs a section on the pitfalls that users
> are likely to run into (like infinite loops).

It seems that if we go down this route, though, then what we really need is a big, bold warning at the top of the Alternative class saying something like, "Do *not* implement this class for your type unless you *really* know what you are doing, which will probably only true if you are writing a parser.  If you fail to heed this advice, then many and some will almost assuredly be broken for your type, which will cause code using it to have infinite loops."

Cheers,
Greg
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