Thomas Davie wrote:
Advantages of Yampa: • Just at the moment, slightly more polished. • (maybe) harder to introduce space/time leaks.
Advantages of Reactive: • More functional programming like -- doesn't require you to use arrows everywhere, and supports a nice applicative style. • In very active development. • Active community.
I have not used Reactive as such, but I did use "Classic FRP" extensively, and as far as I know the setup is similar, even if Reactive has a modern and more principled interface. Based on my Classic FRP experience (which may be out of date, if so, correct me), I'd say advantages of Yampa are: * More modular. Yampa's signal function type is explicitly parameterized on the input signal type. In Classic FRP and Reactive (as far as I know), the system input is implicitly connected to all signal functions (or behaviours) in the system. One consequence of this is that it there were issues with reusing Classical FRP for different kinds of systems inputs, and difficult to combine systems with different kinds of input. This was what prompted a parameterization on the type of the system input in the first place, which eventually led to Arrowized FRP and Yampa. I don't know what the current story of Reactive is in this respect. But having parameterized input has been crucial for work on big, mixed-domain, applications. (For example, a robot simulator with an interactive editor for setting up "the world". The robots were FRP systems too, but their input is naturally of a different kind that the overall system input. It also turned out to be very useful to have an FRP preprocessor for the system input, which then was composed with the rest of the system using what effectively was arrow composition (>>>), but called something else at the time.) * A clear separation between signals, signal functions, and ordinary functions and values, yet the ability to easily integrate all kinds of computations. Arguably a matter of taste, and in some ways more a consequence of the Arrow syntax than Arrows themselves. But in Classical FRP, one had to do either a lot of explicit lifting (in practice, we often ended up writing lifting wrappers for entire libraries), or try to exploit overloading for implicit lifting. The latter is quite limited though, partly due to how Haskell's type classes are organized and that language support for overloaded constants is limited to numerical constants. In any case, when we switched to arrows and arrow syntax, I found it liberating to not have to lift "everything" to signal functions first, but that I could program both with signals and signal functions on the one hand, and plain values and functions on the other, at the same time and fairly seamlessly. And personally, I also felt this made the programs conceptually clearer and easier to understand, My understanding is that Reactive is similar to Classical FRP in this respect. * Classical FRP lacked a satisfying approach to handle dynamic collections of reactive entities as needed when programming typical video games for example. Yampa has a way. One can argue about how satisfying it is, but at least it fulfills basic requirements such that allowing logically removed entities to be truly removed (garbage collected). I don't know where Reactive stands here. * There was also an issue with Classical FRP having to do with the need to observe the output from one part of the system in another part of the system. This is quite different from parameterizing the second part of the the system on the first, as this approach loses sharing across switches. This led to the development for "running in" constructs, which effectively made it possible for behaviours to be both signals (i.e. signal functions already applied to the system input), and signal functions (not yet applied to the system input). Yet there was no distinction between these "running behaviours" (= signals) and normal behaviours (= signal functions) at the type level. The approach also led to semantic difficulties, and, when trying to resolve those, to a very complicated design involving complicated overloading and auxiliary classes. The arrows approach obviated the need for all of this, and I consider that and other distinct advantage. Again, I don't know where Reactive stands here, but it needs to have a good answer to this issue, or it is going to suffer from limited expressivity. Many of the above advantages are matters of opinion (but so are the advantages initially put forward for Reactive above). However, the development of AFRP and Yampa was motivated by fundamental expresssivity limitations of Classical FRP, in at least some ways related to the very way the system was set up. To the extent Reactive is similar in style to Classical FRP, I think Reactive also needs to address those questions. All the best, /Henrik -- Henrik Nilsson School of Computer Science The University of Nottingham nhn@cs.nott.ac.uk This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.