Gen

@zzzzbov/gen is a package of generator utility functions to make working with collections easier. It is specifically designed to be used with the proposed pipeline operator (|>). If the pipeline operator isn't available, gen includes a pipe function which can be used instead.

Installation

npm i @zzzzbov/gen

API

• all
• any
• append
• concat
• count
• filter
• integers
• map
• mapMany
• pipe
• prepend
• reduce
• skip
• skipWhile
• splice
• take
• takeWhile
• unique

all

gen.all([test(value, index)])(iterator)

const {all} = require('@zzzzbov/gen')
// or
const all = require('@zzzzbov/gen/all')

The all function takes an optional test function as a parameter and produces a new function. The new function accepts an iterator as a parameter and returns true if every member of iterator passes the test and false if any member of iterator does not pass the test.

Example

const all = require('@zzzzbov/gen/all')

const odd = n => n % 2

const example1 = [1, 2, 3] |> all(odd) // false

const example2 = [1, 3, 5] |> all(odd) // true

If no test is passed, a false function is used (_ => false). This allows all to be used to check for empty collections in parity with any.

Example

const all = require('@zzzzbov/gen/all')

const example1 = [] |> all() // true

const example2 = [1, 2, 3] |> all() // false

any

gen.any([test(value, index)])(iterator)

const {any} = require('@zzzzbov/gen')
// or
const any = require('@zzzzbov/gen/any')

The any function takes an optional test function as a parameter and produces a new function. The new function accepts an iterator as a parameter and returns true if any member of iterator passes the test and false if every member of iterator fails the test.

Example

const any = require('@zzzzbov/gen/any')

const odd = n => n % 2

const example1 = [1, 2, 3] |> any(odd) // true

const example2 = [2, 4, 6] |> any(odd) // false

If no test is passed, a true function is used (_ => true). This allows any to be used to check if the collection is empty.

Example

const any = require('@zzzzbov/gen/any')

const example1 = [] |> any() // false

const example2 = [1, 2, 3] |> any() // true

append

gen.append(...items)(iterator)

const {append} = require('@zzzzbov/gen')
// or
const append = require('@zzzzbov/gen/append')

The append function takes a collection of items as parameters and produces a new generator function. The new function accepts an iterator as a parameter and yields the entire iterator followed by all the items.

Example

const append = require('@zzzzbov/gen/append')

const example = [1, 2, 3] |> append(4, 5, 6)
;[...example] // [1, 2, 3, 4, 5, 6]

concat

gen.concat(...collections)(iterator)

const {concat} = require('@zzzzbov/gen')
// or
const concat = require('@zzzzbov/gen/concat')

The concat function takes a collection of collection as parameters and produces a new generator function. The new function accepts an iterator as a parameter and yields the entire iterator followed by the contents of each of the collections.

Example

const concat = require('@zzzzbov/gen/concat')

const example = [1, 2, 3] |> concat([4, 5, 6], [7, 8, 9])
;[...example] // [1, 2, 3, 4, 5, 6, 7, 8, 9]

count

gen.count(iterator)

const {count} = require('@zzzzbov/gen')
// or
const count = require('@zzzzbov/gen/count')

The count function takes an iterator as a parameter and returns the count of how many items are contained in the iterator.

Example

const count = require('@zzzzbov/gen/count')

;[1, 2, 3] |> count // 3

filter

gen.filter(test(value, index))(iterator)

The filter function takes a test function as a parameter and produces a new generator function. The new function accepts an iterator as a parameter and yields every item in the iterator that passes the test.

Example

const filter = require('@zzzzbov/gen/filter')

const odd = n => n % 2

const example = [1, 2, 3] |> filter(odd)
;[...example] // [1, 3]

integers

gen.integers([start], [end])

const {integers} = require('@zzzzbov/gen')
// or
const integers = require('@zzzzbov/gen/integers')

The integers generator function takes optional start and end parameters. integers yields the integers from start to end inclusive.

const integers = require('@zzzzbov/gen/integers')

const example = integers(1, 5)
;[...example] // [1, 2, 3, 4, 5]

start defaults to 0

end defaults to Number.MAX_SAFE_INTEGER

Given that Number.MAX_SAFE_INTEGER is exceptionally large, iterating over integers without an explicit end may result in an, effectively, endless loop.

For generating a specific number of integers, pair the integers function with the take function:

Example

const {integers, take} = require('@zzzzbov/gen')

const example = integers() |> take(5)
;[...example] // [0, 1, 2, 3, 4]

map

gen.map(transform(value, index))(iterator)

const {map} = require('@zzzzbov/gen')
// or
const map = require('@zzzzbov/gen/map')

The map function takes a transform function as a parameter and produces a new generator function. The new function accepts an iterator as a parameter and yields each item produced by the transform.

Example

const map = require('@zzzzbov/gen/map')

const double = n => n * 2

const example = [1, 2, 3] |> map(double)
;[...example] // [2, 4, 6]

mapMany

gen.mapMany(transform(value, index))(iterator)

const {mapMany} = require('@zzzzbov/gen')
// or
const mapMany = require('@zzzzbov/gen/mapMany')

The mapMany function takes a transform function as a parameter and produces a new generator function. The new function accepts an iterator as a parameter and yields each item in each collection produced by the transform.

Example

const mapMany = require('@zzzzbov/gen/mapMany')

const pair = n => [n, -n]

const example = [1, 2, 3] |> mapMany(pair)
;[...example] // [1, -1, 2, -2, 3, -3]

pipe

gen.pipe(input, ...functions)

const {pipe} = require('@zzzzbov/gen')
// or
const pipe = require('@zzzzbov/gen/pipe')

The pipe function is a utility to act as a stand-in for the pipe operator (|>).

The pipe function takes an input value and a collection of functions and produces the resultant value of passing the output of each function as the input of the subsequent function.

Example

const pipe = require('@zzzzbov/gen/pipe')

const addOne = n => n + 1

const double = n => n * 2

const example = pipe(
  5,
  addOne,
  double
) // 12

prepend

gen.prepend(...items)(iterator)

const {prepend} = require('@zzzzbov/gen')
// or
const prepend = require('@zzzzbov/gen/prepend')

The prepend function takes a collection of items as parameters and produces a new generator function. The new function accepts an iterator as a parameter and yields the items followed by the iterator.

Example

const prepend = require('@zzzzbov/gen/prepend')

const example = [4, 5, 6] |> prepend(1, 2, 3)
;[...example] // [1, 2, 3, 4, 5, 6]

reduce

gen.reduce(reducer(reduction, value, index), initial)(iterator)

The reduce function takes a reducer function and initial value as parameters and produces a new function. The new function accepts an iterator as a parameter and returns the resultant reduction after having passed each value through the reducer along with the output from the previous value.

Example

const reduce = require('@zzzzbov/gen/reduce')

const add = (a, b) => a + b

const example = [1, 2, 3] |> reduce(add, 0) // 6

skip

gen.skip(count)(iterator)

const {skip} = require('@zzzzbov/gen')
// or
const skip = require('@zzzzbov/gen/skip')

The skip function takes a count parameter and produces a new generator function. The new function accepts an iterator as a parameter and skips the first count items in the iterator before yielding the rest of the items in iterator.

Example

const skip = require('@zzzzbov/gen/skip')

const example = [1, 2, 3, 4, 5] |> skip(2)
;[...example] // [3, 4, 5]

skipWhile

gen.skipWhile(test(value, index))(iterator)

const {skipWhile} = require('@zzzzbov/gen')
// or
const skipWhile = require('@zzzzbov/gen/skipWhile')

The skipWhile function takes a test function as a parameter and produces a new generator function. The new function accepts an iterator as a parameter and skips items in the iterator until the test is failed.

Example

const skipWhile = require('@zzzzbov/gen/skipWhile')

const lessThanThree = n => n < 3

const example = [1, 2, 3, 4, 5] |> skipWhile(lessThanThree)
;[...example] // [3, 4, 5]

splice

gen.splice(start, deleteCount, ...items)(iterator)

const {splice} = require('@zzzzbov/gen')
// or
const splice = require('@zzzzbov/gen/splice')

The splice function takes a start index, deleteCount, and optional additional items as parameters and produces a new generator function. The new function accepts an iterator as a parameter and splices in any new items at the start index. The generator will then skip over the number of items specified by deleteCount before yielding the rest of the collection from the iterator.

Example

const splice = require('@zzzzbov/gen/splice')

const example = [1, 2, 3] |> splice(1, 1, 2.1, 2.2, 2.3)
;[...example] // [1, 2.1, 2.2, 2.3, 3]

take

gen.take(count)(iterator)

const {take} = require('@zzzzbov/gen')
// or
const take = require('@zzzzbov/gen/take')

The take function takes a count parameter and produces a new generator function. The new function accepts an iterator as a parameter and yields the first count items in the iterator.

Example

const take = require('@zzzzbov/gen/take')

const example = [1, 2, 3, 4, 5] |> take(3)
;[...example] // [1, 2, 3]

takeWhile

gen.takeWhile(test(value, index))(iterator)

const {takeWhile} = require('@zzzzbov/gen')
// or
const takeWhile = require('@zzzzbov/gen/takeWhile')

The takeWhile function takes a test function as a parameter and produces a new generator function. The new function accepts an iterator as a parameter and yields items in the iterator until the test is failed.

Example

const takeWhile = require('@zzzzbov/gen/takeWhile')

const lessThanThree = n => n < 3

const example = [1, 2, 3, 4, 5] |> takeWhile(lessThanThree)
;[...example] // [1, 2]

unique

gen.unique(iterator)

const {unique} = require('@zzzzbov/gen')
// or
const unique = require('@zzzzbov/gen/unique')

The unique generator function takes an iterator and yields each unique value in the order they appear in the iterator.

Example

const unique = require('@zzzzbov/gen/unique')

const example = [1, 2, 1, 3, 1] |> unique
;[...example] // [1, 2, 3]