transducers

The primary goal of transducers is to run a pipeline of transformations of an input stream of values without creating intermediate values. The functions describing computations are decoupled, so this makes program design cleaner and easier to develop and maintain.

A transducer is a function that accepts a transformer and returns a transformer and can be composed directly

Transducers can:

• Be Composable
• They only enumerates over the elements onces (very efficient for working with data streams)
• can be use for lazy or eager evaluation
• You can combine transducer to generate another transducer (High order reducers ¿?)

There are two strategies:

• Pull: lazy evaluation
• Push: eager evaluation

Pull waits until a consumer asks for the next value (for example an Iterable)

Push enumerates over the source values and pushes them through the tubes ASAP (Array.reduce())

Transducers compose top to bottom (left to right)

Example:

Given an array of autobots we want to:

1. filter out values that don’t contain the letter ‘r’,
2. uppercase
3. reverse each value

First approach without a tranducer

const R = require("ramda"); // Ramda functional library

let autobots = [
  "Optimus Prime",
  "Bumblebee",
  "Ironhide",
  "Sunstreaker",
  "Ratchet",
];

// Filter for autobots that contain 'r', uppercase, then reverse
let transform = R.compose(
  R.filter((x) => /r/i.test(x)),
  R.map(R.toUpper),
  R.map(R.reverse)
);

transform(autobots);
// => [ 'EMIRP SUMITPO', 'EDIHNORI', 'REKAERTSNUS', 'TEHCTAR' ]

Same approach with tranducer

const R = require("ramda"); // Ramda functional library

let autobots = [
  "Optimus Prime",
  "Bumblebee",
  "Ironhide",
  "Sunstreaker",
  "Ratchet",
];

// Filter for autobots that contain 'r', uppercase, then reverse
let transform = R.compose(
  R.filter((x) => /r/i.test(x)),
  R.map(R.toUpper),
  R.map(R.reverse)
);

transform(autobots);
// => [ 'EMIRP SUMITPO', 'EDIHNORI', 'REKAERTSNUS', 'TEHCTAR' ]

We get the same exact result (in this situation), but something very different and very powerful is happening under the hood. In the first example, the entire list was transformed at each step.
This means that we had to iterate over the list three times. However, in the second example where we used the transducer, we only had to iterate over the list once!