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    Funfix is a library of type classes and data types for Functional Programming in JavaScript, TypeScript and Flow.

    Inspired by Scala, Cats and Monix.


    The code is organized in sub-projects, for à la carte dependencies, but all types, classes and functions are exported by funfix, so to import everything:

    npm install --save funfix

    Or you can depend on individual sub-projects, see below.

    Modules: UMD and ES 2015

    The library has been compiled using UMD (Universal Module Definition), so it should work with CommonJS and AMD, for standalone usage in browsers or Node.js.

    But it also provides a module definition in package.json, thus providing compatibility with ECMAScript 2015 modules, for usage when used with a modern JS engine, or when bundling with a tool chain that understands ES2015 modules, like Rollup or Webpack.


    Funfix has been split in multiple sub-projects for à la carte dependency management. As mentioned above, you can depend on everything by depending on the funfix project.

    These sub-projects are:



    Exposes primitive interfaces and data types that need to be universally available, belonging into a standard library.

    See JSDoc documentation.

    Quick Overview & Usage

    npm install --save funfix-core

    Exposes types for expressing disjunctions:

    Either data type for expressing results with two possible outcome types (a disjoint union)
    Option data type for expressing optional values
    Try data type for representing the result of computations that may result in either success or failure

    Standard interfaces and tools for dealing with universal equality and hash code generation:

    IEquals an interface for defining universal equality and hash code
    is and equals for using IEquals in tests, or otherwise falls back to JavaScript's equality (== or valueOf())
    hashCode for calculating hash codes (for usage in sets and maps data structures) using IEquals, or otherwise falls back to calculating a hash from .valueOf() or from .toString()
    isValueObject for testing if a given object implements IEquals

    Standard, reusable error types, that help with some common scenarios, working with error types being preferable to working with strings:

    DummyError for tagging errors used for testing purposes
    IllegalArgumentError for signaling that a given argument is violating the contract of the called function or constructor
    IllegalInheritanceError for signaling that inheriting from a certain class is illegal
    IllegalStateError for signaling that an illegal code branch was executed and thus something is wrong with the code and needs investigation (e.g. a bug)
    NoSuchElementError thrown when the user expects an element to be returned from a function call, but no such element exists
    NotImplementedError thrown in case an implementation is missing
    TimeoutError thrown in case the execution of a procedure takes longer than expected
    CompositeError for gathering multiple errors in a single reference that can expose them as a list

    Misc utilities:

    applyMixins for working with mixins (i.e. classes used as interfaces, with methods that have default implementations), see Mixins for an explanation
    id is the "identity" function



    Contains low level / side-effectful utilities and data types for building higher level concurrency tools.

    See JSDoc documentation.

    Quick Overview & Usage

    npm install --save funfix-exec

    Scheduling tasks for asynchronous execution:

    Future a lawful, fast, cancelable alternative to JavaScript's Promise
    Scheduler the alternative to using setTimeout for asynchronous boundaries or delayed execution

    In support of futures and schedulers, ICancelable data types are introduced for dealing with cancellation concerns:

    ICancelable and Cancelable for expressing actions that can be triggered to cancel processes / dispose of resources
    IBoolCancelable and BoolCancelable for cancelable references that can be queried for their isCanceled status
    IAssignCancelable and AssignCancelable for cancelable references that can be assigned (behave like a box for) another reference
    MultiAssignCancelable being a mutable cancelable whose underlying reference can be updated multiple times
    SingleAssignCancelable for building forward references, much like MultiAssignCancelable except that it can be assigned only once, triggering an error on the second attempt
    SerialCancelable being like a MultiAssignCancelable that cancels its previous underlying reference on updates

    And also types for expressing durations:

    TimeUnit inspired by Java's own enumeration, representing time
    Duration inspired by Scala's own type, as a type safe representation for durations



    Defines monadic data types for controlling laziness, asynchrony and side effects. Exposes the most advanced IO implementation for JavaScript.

    See JSDoc documentation.

    Quick Overview & Usage

    npm install --save funfix-effect

    The exposed data types:

    Eval lawful, lazy, monadic data type, that can control evaluation, inspired by the Eval type in Typelevel Cats and by the Coeval type in Monix, a more simple IO-like type that can only handle immediate execution, no async boundaries, no error handling, not being meant for suspending side effects.
    IO lawful, lazy, monadic data type, capable of expressing and composing side effectful actions, including asynchronous, being the most potent and capable alternative to JavaScript's Promise, inspired by Haskell's IO and by the Monix Task

    TypeScript or Flow?

    Funfix supports both TypeScript and Flow type annotations out of the box.

    It also makes the best use of the capabilities of each. For example TypeScript has bivariant generics, but Flow supports variance annotations and Funfix makes use of them. Development happens in TypeScript, due to better tooling, but both are first class citizens.


    The Funfix project welcomes contributions from anybody wishing to participate. All code or documentation that is provided must be licensed with the same license that Funfix is licensed with (Apache 2.0).

    Feel free to open an issue if you notice a bug, have an idea for a feature, or have a question about the code. Pull requests are also gladly accepted. For more information, check out the contributor guide.


    All code in this repository is licensed under the Apache License, Version 2.0. See LICENCE.


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