Mark partial functions as such

[Henning Thielemann]

On Fri, 31 Aug 2018, Oliver Charles wrote:

> On Fri, Aug 31, 2018 at 5:21 PM Tikhon Jelvis <tikhon at jelv.is> wrote:
>
>> Deeper questions of partiality aside, if a function can throw 
>> exceptions, the documentation should spell this out *explicitly*, 
>> ideally also specifying what the type of the exception may be. To me, 
>> this is a *minimum* standard to expect from documentation in any 
>> language with exceptions.

'error' is not an exception, it is an undefined value. 'error' is only a 
debugging convenience that would otherwise be an infinite loop. It should 
not be necessary to distinguish them in production code.