Re: [boost] Monad (was: Re: [Boost-users] [afio] Formal review of Boost.AFIO)

-----Original Message----- From: Boost [mailto:boost-bounces@lists.boost.org] On Behalf Of Andrey Semashev Sent: 25 August 2015 15:12 To: boost@lists.boost.org Subject: Re: [boost] Monad (was: Re: [Boost-users] [afio] Formal review of Boost.AFIO)

On Tue, Aug 25, 2015 at 3:44 PM, Niall Douglas wrote:

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On 25 Aug 2015 at 0:02, Giovanni Piero Deretta wrote:

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It's a C++ monad designed for C++ programmers writing in C++.

Niall, you are missing the point: the reason that your monad can't be the true definition of a Monad is that no type can.

No, that's exactly why I chose that name for the library. I absolutely get the point.

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That there is no such a thing as Monad type in Haskell at all; there is a type *class* named Monad. In Haskell there are many concrete types that are instances of the Monad type class (list, Maybe, IO). Other languages are similar: I believe you are familiar with rust, in that language Monad would be a trait.

Similarly, in C++ you can have multiple types[1] (option, future, etc...) that model the Monad concept (Haskell type classes loosely map to C++ concepts), but calling any of them (or a template type) a Monad, makes at much sense as having a class named RegularType.

Again, exactly why I chose it: it makes no sense.

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In C++, you could argue that 'monad' would be a decent name for type erased wrapper over any type that model the Monad concept, but I do not believe that your monad type is that.

Now, afio::monad, while not great, at least suggests that we are talking about the Monad of Asynchronous File IO [2].

C++ is not a functional programming language and never will be, and I even think nor should it be.

I certainly don't get anything like as worked up about naming as people are getting over this. Who cares if it doesn't pollute namespace, is short to type and isn't going to get confused with something else?

That's why value<T> or holder<T> or return_<T> all got ruled out. They will confuse. monad<T> is nonsense name, but it stands out nicely in code and let's the eye quickly check that your logic is correct.

As monad<T>'s main use case for me so far at least is exception safety management, it NEEDS to stand out from surrounding code as a return type from a function.

But let me clear, if anyone can suggest a similarly short, instantly recognisable, uniquely standout name for monad<T>, I'm all ears.

For example, I have toyed with donkey<T> instead of monad<T>. Also a nonsense name, but it does the donkey work of exception safety for you (with monadic programming extensions) and it has all the features of standing out from surrounding code, being quick to type and so on.

Would people prefer Boost.Monad => Boost.Donkey, and monad<T> => donkey<T>?

The reason I didn't choose donkey<T> is because I thought people wouldn't take a Boost.Donkey library seriously, and that would be a shame as I'm finding it an enormous productivity aid. It also doesn't fit to have a lightweight fast Concurrency TS implementation in a library called Boost.Donkey.

But I also don't think the naming war on this library can be won. If Boost.Donkey will stop the war and make people vote for acceptance, I'll take Boost.Donkey over Boost.Monad any day.

I don't know Haskell or what monad means there, so to me monad<> does not stand out, apart from that I don't know what it means. That's probably because there are lots of things that I don't know or understand, so there's nothing special about it. :)

However, reading your argument I don't see the rationale behind choosing the name which overloads what apparently is a well understood term in Haskell. If the meaning of your monad<> differs from that well established understanding then this will certainly lead to confusion and endless questions and notes like 'that C++ monad is not the monad you know'. To me this indicates that the naming choice is poor.

So my point is name it donkey, if you feel this name reflects the component purpose well (I doubt it). Pick another name that is not overloaded yet or has close semantics. Only keep monad if it doesn't cause confusion.

Absolutely right. Anything but monad! It *does* cause confusion. Think again - and donkey won't do either ;-) Paul --- Paul A. Bristow Prizet Farmhouse Kendal UK LA8 8AB +44 (0) 1539 561830