tsfun - functional combinator library for TypeScript

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tsfun aims at providing simple functional programming idioms in a way which fit well with the literal based data structures [] and {} of JavaScript while at the same time providing accurate TypeScript-typings.

Getting started

Install

$ npm i tsfun

Pick your functions

import {on, equal, take, update, flow} from 'tsfun'

Or import as module

import * as tsfun from 'tsfun'

Intro

JavaScript has two collection data structures which can be created using literals. Those are Arrays ([]) and Objects ({}). We assume Arrays to be non-sparse. Objects, at least from the perspective taken in tsfun, do not include class instances (anything else created with new, apart from Object, so Array and Date would not count as an Object here).

Those data structures provide the ground for a couple of abstractions.

First, Arrays and Objects can be seen as Associatives, meaning they both have keys (indexes, i.e. numbers, in the Array case) as well as (homogeneous, i.e. same-typed) values. For Arrays we have Array<T> in TypeScript. To encode a view on Object as an associative collection, tsfun provides Map<T>, analogously. Order in Maps does not matter, while in Arrays it does. Arrays seen this way are taken as Lists or Vectors (based on their JavaScript properties). There is however another view on Arrays, which is the Set-view, where order does not matter.

Second, Array and Objects can be seen as Records, meaning there are a couple of properties, which have distinctive meanings and types. Think of a Person with the name and age properties for example. Analogously, there exists a view on Arrays, which is the Tuple-view, where the position in the (small) Array has a meaning. Both variants are supported by the TypeScript type system.

Third, there is Struct, which is a mutually nested structure of Tuples and Records.

tsfun revolves around dealing with these data structures and views on them and provide various functions which operate on these abstractions.

Leafs in any of these structures can be of types number, string, boolean, null, undefined, which is denoted by the type Primitive. Class instances of anything other than Array or Object (which are assumed to be created via literals) are treated as illegal arguments generally.

Note: We ignore the JavaScript Map collection and the TypeScript Record type.

Functions

Array

• first
• rest
• last
• reverse
• separate
• distribute
• flatten
• flatMap
• take
• takeWhile
• takeRight
• takeRightWhile
• drop
• dropWhile
• dropRight
• dropRightWhile
• takeNth
• takeUntil
• append
• prepend
• zip
• range
• dense
• sort

Associative

Associatives are homogeneous (i.e. all values of the same type) Arrays and homogeneous Maps (JavaScript-Objects).

• keys
• values
• keysValues
• copy
• count
• prune
• size
• indices
• all
• any
• lookup
• map
• reduce
• filter
• remove
• forEach
• assoc

Composition

Tools for combining curried versions of tsfun functions into larger units.

• flow
• compose
• pipe
• curry
• cond
• conds
• identity
• apply
• collect
• val
• nop
• throws

Struct

Structs are TypeScript-Tuples (which are JavaScript-Arrays), and JavaScript Objects, typed via TypeScript-Interfaces, as well as combinations, i.e. mutual nestings, thereof. Leafs can be of types number, string, undefined, null, boolean.

• to
• update
• clone
• detach

Set

JavaScript-Arrays, viewed as sets. Obviously because of the choice of these should be seen as convenience functions for smaller sets.

• set
• intersection
• intersect
• subtract
• union
• unite
• duplicates

Tuple

JavaScript-Arrays, typed as TypeScript-Tuples.

• singleton
• value
• pair
• left
• right
• swap
• pairWith
• tuplify

Fallible

JavaScript-Arrays, typed as TypeScript-Tuples. Used for processes that can fail.

• just
• nothing
• success
• failure
• ok
• err

Predicate

Predicates generally are functions of type (t: T) => boolean, which can be passed to higher order functions like filter, for example.

Composition

• isNot
• not
• and
• or
• xor

Defined & Empty

• isEmpty
• isUndefinedOrEmpty
• isDefined
• isUndefined

Types

• isArray
• isObject
• isString
• isNumber
• isBoolean
• isFunction
• isPrimitive
• isAssociative

Tuple

• isSingleton
• isPair

Fallible

• isOk
• isErr
• isEither
• isMaybe

Comparator

Comparators generally are functions of type (l: T1) => (t: T2) => boolean.

Reference

• is
• isnt

Array

• subsetOf
• supersetOf
• sameset
• includes
• includedIn
• startsWith
• endsWith
• same

Map

• samemap

Struct

• equal
• on

Number

• gt
• lt
• gte
• lte

Types

Data

• Map
• Associative

Functions

• Predicate
• Mapping
• Filter
• Effect

Tuple

• Singleton
• Pair

Fallible

• Maybe
• Just
• Nothing
• Either
• Success
• Failure
• Ok
• Err

Constants

Tuple

• L
• R

Extra functions

Async

• aMap
• aFilter
• aReduce
• aFlow
• aCompose

More

See Fallible, Lazy

Build & Test

$ npm run build && npm t

or

1$ npm run build:watch
2$ npm t

Credits

The way of thinking about datastructures I owe mostly to working with Clojure. I tried to mimic some principles but without sacrificing any convenience with regards to the use of the existing collection literals. The writing of library functions like this and the thinking about typing I encountered first and thus attribute mostly to Functional Programming in Scala (the red book).

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