Library for higher-order manipulation of collections, based upon reduce.
Most functional languages (including beloved JS) typically come with some collection transformation functions like filter and map that take a logical collections and return transformed version of it. Unfortunately they tend to complect, by implying mechanism, order, laziness and representation. This library is an attempt to provide simple solution for some of the hard problems by decomplecting and building upon simple premise - minimum definition of collection is something that is reducible.
More specifically library defines super-generalized and minimal abstraction for
collections - a collection is some set of things that, when given a function to
apply to its contents, can do so and give you the result, i.e. a collection is
(at minimum) reducible. In other words, you can call
reduce on it.
A very minimal abstraction for collection is more powerful than it may seem at first!
Demonstration of features of this library requires some basic understanding of
the abstraction above. So let's take a more practical look at the idea. Let's
say we have a
reduce function with (very familiar) API:
// => accumulated result
It takes reducing function, a reducible
initial value to
accumulate reductions upon. In return it outputs an accumulated result.
Reducing functions performing accumulation have a following shape:
// => new result
A reducing function is simply a binary function, akin to the one you might pass
to reduce. While the two arguments might be treated symmetrically by the
function, there is an implied semantic that distinguishes the arguments:
the first argument is a
result or accumulator that is being built up by the
reduction, while the second is some new input
value from the source being
All of the collection operations can be expressed in terms of transformations.
By the definition all transformations will produce reducible collections
that can be reduced via
reduce function defined above:
// => reducible collection// => reducible collection
In order to explain transformations we'll need a primitive API for producing
reducible collections. Let's define one in form of
accumulator function and returns something that can be reduced
// => reducible
Argument it takes,
accumulator is a function that performs has following shape:
// => accumulated result
And when invoked it performs reductions via
next reducing function starting
Now consider following implementation of
There are a few things to note here:
- Type of the source is irrelevant as long as it is reducible and there for
can be reduced via
- Transformations do not traverse collections, instead they compose results that can be reduced by a receiver of the result later.
- Transformations do not imply timing in which
reducerin invoked with an each
source, there for
sourcecan be asynchronous.
- Filtering can skip inputs by simply returning the incoming result.
Library consists of transformation functions which, as seen above, when called do nothing except the creation of a recipe for a new collection, a recipe that is itself reducible. No work is done yet to the contained elements and no concrete collection is produced. All the transformations defer actual work to a point where result of transformations pipeline is being reduced.
The beautiful thing is that this mechanism also works for all other traditional
merge etc. Note the fact that
(potentially) contractive, and flatten is (potentially) expansive per step -
the mechanism is general and not limited to 1:1 transformations.
Transformation functions are absolutely agnostic of the actual type of the
source, as they just describe transformations and leave it up to
to do a reduction when result is consumed.
Library takes a advantage of this feature and takes it even step further by
treating every possible value as a reducible collection. Non collection values
like numbers, booleans, objects etc. are treated as collection of single item,
item being a value. Also
undefined are considered as empty
This means that library can be used on any data type and more importantly transformations between different data types & compose naturally, which is great, let's you define logic in terms of abstractions instead of specific types.
All the transformations are fully composable as a matter of fact transformation pipelines produce compositions equivalent of a function compositions created by a compose. Also type agnostic nature of the transformation functions enables compositions between different types of data.
Since transformations doesn't do the work, but merely create a recipe, there is no per-step allocation overhead, so it's faster. Also note that transformations are composed by curring transformation functions and all the actual work happens in a pipe line at the end when result is consumed, which means that no intermediate collections are produced, unlike it's a case with arrays etc..
It can even outperform arrays when used wisely, although it's not the point & arrays are not the primary use case.
As it was already pointed out transformation functions do not imply any timing of individual value delivery, which means they can be used on asynchronous data structures like node streams or FRP events & signals.
Even better actually exact same code can be used with both synchronous and
asynchronous data structures. For example exact same code in fs-reduce
can be forced to do blocking IO by via
Since transformations are
source type agnostic it's highly extensible. In
fact implementation is based of polymorphic method dispatch library and
enables one to add support for new data types without any changes to this
library or data types / classes them self. This feature is used by
stream-reduce library to add support for node streams. There are more
examples of this feature in callback-reduce, dom-reduce,
Very likely all data types like
signal provided by this library will be move
out into own libraries too.
Reducible data structures feature auto cleanup of the resources at the end of consumption. For example dom-reduce and fs-reduce use this feature to remove event listeners / close file descriptors once input is consumed and to set you free from clean up constraints. This means you spend more time on actual problems rather and less on plumbing.
Infinite data structures can be trivially represented via reducibles since nothing implies the end. In fact dom-reduce uses this feature to represent user events in form of reducibles that pretty much can be infinite.
That being said reducibles are not the best abstraction for the some types of infinite data structures specially ones that rather better be polled instead.
1. Q: Can this handle "back pressure" ?
A: Short answer is Yes.
See IO Coordination for more detailed answer
npm install reducers