readme.js

December 28, 2021 · View on GitHub

/**

callbag-scan
Callbag operator that combines consecutive values from the same source.
It's essentially like array .reduce, but delivers a new accumulated value
for each value from the callbag source. Works on either pullable or
listenable sources.
npm install callbag-scan
Example:

const fromIter = require('callbag-from-iter');

const forEach = require('callbag-for-each');

```
const scan = require('callbag-scan');
```

const iterSource = fromIter([1,2,3,4,5]);

const scanned = scan((prev, x) => prev + x, 0)(iterSource);

forEach(x => console.log(x))(scanned);    // 1

                                          // 3

                                          // 6

                                          // 10

                                          // 15

*/

function scan(reducer, seed) { let hasAcc = arguments.length === 2; return source => (start, sink) => { if (start !== 0) return; let acc = seed; source(0, (t, d) => { if (t === 1) { acc = hasAcc ? reducer(acc, d) : ((hasAcc = true), d); sink(1, acc); } else sink(t, d); }); }; }

module.exports = scan;