kbeaty's comments

You may be interested in going through "A General Theory of Reactivity"[0] from Kris Kowal, creator of the q promise library. It discusses relationships between streams, promises, iterators and generators (although the streams that he discusses are not how Node.js streams are implemented)

[0]: https://github.com/kriskowal/gtor

While I am currently trying to teach myself Haskell for exactly this reason (understand the "real big picture" in FP), I don't know if there is much harm in starting the journey by exploring some FP concepts in languages one is already familiar with, despite how lacking the language is in that regard. This presentation does point out many features that JavaScript lacks from "true FP" languages.

I, for one, don't know if I would have ever tried to start learning Haskell if I didn't discover some of the benefits of FP first hand through a familiar language.

You can indeed use transducers in asynchronous contexts. In fact, that is what intrigues me most about the abstraction.

Transducers are defined such that you can abstract the context of input, output and iteration and focus on the transformation of each element from an independent source individually. The implementation of each transducer accepts another transformation in a "pipeline" (eventually the output sink) and accepts an input during an external iteration process. The implementation decides what to do with it (map changes with a function, filter ignores certain values with a predicate, etc.) You can also define transducers that send multiple values for each input (think string.split) or some that do not send any until completion (think buffered results).

Since the iteration source and sink are abstracted from the transformation, you can use the same transformation in other contexts (Promises, event streams, IO streams, CSP, etc.)

I've been experimenting with transducers in asynchronous contexts in JavaScript if anyone is interested, for example:

[1]: http://simplectic.com/projects/underscore-transducer/ [2]: http://simplectic.com/projects/underarm/ [3]: https://github.com/transduce/transduce-async [4]: https://github.com/kevinbeaty/transduce-stream [5]: https://github.com/transduce/transduce-push [6]: https://github.com/transduce/transduce-then

There is also Transducers Explained [1] if you are familiar with JavaScript.

(Shameless plug in the hope it may be helpful to someone)

[1]: http://simplectic.com/blog/2014/transducers-explained-1/

For another take on Reactive Programming from Erik Meijer, check out "Duality and the End of Reactive" [1] (video).

I watched it just last night and found it very thought provoking (so much that I stole some of the concepts to create transduce-async [2] this morning).

[1]: http://channel9.msdn.com/Events/Lang-NEXT/Lang-NEXT-2014/Key... [2]: https://github.com/transduce/transduce-async

In regards to Bacon.js, tel had a very interesting response discussing transducers in relation to FRP/Reactive Programming in another thread [1].

[1]: https://news.ycombinator.com/item?id=8447046

Thanks, that explains a lot. Very interesting indeed.

Very interesting. I certainly have some reading to do.

Can you explain a little more the notion discrete values and sampling rates and how that applies to stream processing? I assume that it applies to sampling values of a process over time, but what would be an example in computation where the value would be considered continuous? Is it similar to continuous vs discrete signal processing?

[Edit]: change "form of FRP" to "form of reactive programming" as I'm not sure I know the true notion of "FRP" based on tel's response.

You could probably say that this library implements a form of reactive programming using transducers with `asCallback` and `asyncCallback`. In fact, many ideas for this library were rooted in my exploration of ReactiveCocoa a few years back [1]. I think that transducers lead to a much cleaner implementation and I may resurrect that library to be based on underscore-transducer and add more reactive extensions. (Also, the 'r' in `_r` stands for "reactive".)

I really like the way transducers abstract the process of iteration from the transformation that makes this possible.

[1]: https://github.com/kevinbeaty/underarm

[Edit]: explain step function and memo when mentioning map.

A transducer is composable algorithmic transformation, that is independent of input and output sources and the process of iteration [1].

The threading macro `-->` reorders execution of a list of forms, inserting the first form as the last item of the second, etc. Composition of transducers apply transformations in the same order.

Essentially all transducer transformations are defined as a series of steps, where each step is possibly advanced (0 or more times) by each transformation by a function similar to what you pass `reduce`: `memo = step(memo, item)`. When you execute a transducer, you supply the step function, the initial memo, and each item when iterating. This allows you to abstract the input, output, and iteration outside the transformation (these are implementation details normally provided by the library).

You can define `map` as a form of `reduce`: `memo = step(memo, mappingFn(item))`, which allows you to create a transducer for `map`.

Remember that the step function and initial memo are supplied outside the transformation. But, as an example, if you are transducing over arrays, the initial memo is an empty array, the step function appends each item to the array and returns the modified array, and the return value is used as the memo (result) of the next iteration of `step`. This step function is executed for every item in a source array using some process of iteration (normally a reduce, but does not have to be).

[1]: http://clojure.org/transducers

Transducers allow the abstraction of algorithmic transformations independent from the input and output, and even the process of iteration.

Whereas lodash operates on arrays and objects calculating intermediate results, transducers simply define the transformation in terms of functions similar to what you pass reduce: start with a memo, execute a function with a memo and an item, return the possibly transformed memo for the next iteration. Once you abstract the transformation away from the data, you can apply the same transformations to different processes that start with an initial value and step through a result. One benefit is that you can compute the result in one pass (without intermediate results). Another is you can use the same transformation in different contexts (lazy lists, indefinite sequence generation, CSP, event streams, etc.).

The source could be anything that produces a sequences of values: streams, iterators, callbacks, immutable-js, etc. You simply have to define (external to the transducer) how you append each item to the supplied result. The "step function" that knows how to append results to values is passed to the transducer, and the transducer executes the step function when reducing over results.

It's interesting you mention lodash in the context of transducers, as I have been developing my own take on transducers closely following the underscore API [1].

[1]: https://github.com/kevinbeaty/underscore-transducer

The sysstat suite [1] is quite handy for single nodes. Includes utilities to monitor system performance and activity over time.

[1]: http://sebastien.godard.pagesperso-orange.fr/documentation.h...

A year or two ago I created a very similar language [1] in collaboration with my kids, then aged 8 and 10. They had a lot of fun writing their own stories and "telling computers what to do". The oldest has since moved on to writing her own HTML and CSS. Hoping to keep the fire alive.

A few more ideas that I never got around to, feel free to take or leave them:

* A simple tool to draw characters. My kids liked Google drawings more than Paint. They didn't mind (at first) that the drawings weren't animated.

* Sharing stories with family and friends

* Drawing backgrounds, moving between scenes, animation editor.

* They liked the idea of writing a story, but very quickly wanted to build a game. An animation editor could introduce looping. Collisions could introduce conditional actions, etc.

Good luck. It's a lot of fun.

[1]: http://kevinbeaty.net/projects/storyturtle/