JS Transducers

transducers.js

const arrayReducer = (arr, elemnt) => arr.concat(elemnt)
arrayReducer.baseCase = []
const stringReducer = (string, string2) => string + string2
stringReducer.baseCase = ""
const functionReducer = (value, f) => f(value)

const mapTransducer = (f) => (reducer) => (acc, curr) => reducer(acc, f(curr))

const filterTransducer = (f) => (reducer) => (acc, curr) => f(curr) ? reducer(acc, curr) : acc

const filterEvenTransducer = filterTransducer((n) => n % 2)
const mapIncTransducer = mapTransducer((n) => n + 1)

const filterShortTransducer = filterTransducer((s) => s.length < 3)
const mapToUpperCaseTransducer = mapTransducer((s) => s.toUpperCase())

const compose = (...fs) => (arg) => fs.reduceRight(functionReducer, arg)

console.log(
    'Composing transducers: filterEvenTransducer with mapIncTransducer into an arrayReducer',
    [11, 22, 33, 44].reduce(
        compose(
            filterEvenTransducer,
            mapIncTransducer
        )(arrayReducer),
        arrayReducer.baseCase
    )
)
// [12, 34]

console.log(
    'Composing transducers: filterShortTransducer with mapToUpperCaseTransducer into a stringReducer',
    ["fa", "fee", "fi", "foo", "fuuu"].reduce(
        compose(
            filterShortTransducer,
            mapToUpperCaseTransducer
        )(stringReducer),
        stringReducer.baseCase
    )
)
// FAFI

console.log(
    'Composing transducers: filterShortTransducer with mapToUpperCaseTransducer into an arrayReducer',
    ["fa", "fee", "fi", "foo", "fuuu"].reduce(
        compose(
            filterShortTransducer,
            mapToUpperCaseTransducer
        )(arrayReducer),
        arrayReducer.baseCase
    )
)
// ["FA", "FI"]