Mark partial functions as such

[Bardur Arantsson]

On 31/08/2018 18.59, 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.
> 
> Is this to be applied transitively? It has to be, to meet your
> criteria, but this is a fairly unrealistic expectation to put on
> library authors. If it's not applied transitively, then the
> documentation creates a false sense of security - "catch these
> exceptions that *I* throw and you're good!". I really think this part
> of exceptions is a tooling problem that we have to solve. Haddock
> should be responsible for figuring this out.
> 

Not to mention the issues of "may throw" declarations for higher-order
functions... (Java checked exceptions are basically broken[1] because of
this. Well, this + the variance issues arising from inheritance and
method signatures, but obviously Haskell doesn't have inheritance, so...)

Regards,

[1] They even break "catch" because everybody is forced to wrap
"checked" exceptions in a RuntimeException if signatures don't specify
"may throw anything", so you *also* have to check for wrapped exceptions
in "catch" clauses. Anyway...