On Sat, 10 Feb 2007, Jon Harrop wrote:

> On Friday 09 February 2007 21:55, Brian Hurt wrote:
>> let rec amb = function
>>
>>     | [] -> None
>>     | h :: t ->
>>
>>        let r =
>>           try
>>              Some(h ())
>>           with
>>
>>              | _ -> None
>>
>>        in
>>        match r with
>>
>>        | None -> amb t
>>        | Some(_) as e -> e
>>
>> As a slightly better implementation.
>
> I think you're trying to box the returned value in order to evade non-tail
> recursion but the OPs function was actually already tail recursive because
> the recursive call to "amb" occurs outside the try..with.

He was doing the boxing on the return as well.  And note, in the above 
code I only box once.

Brian