std.sumtype?

[Steven Schveighoffer]

On 3/30/21 12:32 PM, Paul Backus wrote:

>> Separate thing - I think the catch-all handler could be a bit better 
>> documented. Is the lack of a type that triggers it? Or is underscore 
>> ('_') special (ala Scala). If the latter, then are the '_1' and '_2' 
>> forms shown in the multiple dispatch examples special? (I'm guessing 
>> that there's nothing special about the underscore forms, but people 
>> familiar with Scala might assume some else.) I'm looking at the docs 
>> here: https://pbackus.github.io/sumtype/sumtype.SumType.html.
> 
> Your guess that the underscore is not special is correct. This should be 
> clear from reading the documentation for match [1], but I expect there 
> are many users who read only the examples and skip the prose, so it 
> would be best to add a note about this to the examples as well.
> 

What might be nice is to have some simplifiers for match to prevent 
having to jump through the hoops.

For example, a match flavor that throws by default, or one that ignores 
unhandled types. This way, you don't have to write stuff like `(_) {}` 
at the end of your handlers.

FWIW, taggedalgebraic has `visit` to enforce all items are handled, and 
`tryVisit` that throws if at runtime it determines no visitors match the 
current type.

-Steve