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    1.6.0 • Public • Published


    A library for functional programming in TypeScript. Curried, argument-last, pure, total functions that never mutate any data, Maybe/Either/Chain monads, FutureEither/FutureMaybe monad-likes.

    There's not enough JavaScript libraries to choose from. -- no one, never

    This is a quick implementation of most of the FP tools I need in may daily work. Typings are kept as as simple as possible, although this may include some dirty castings under the hood. Still, it is quite shiny when seen from the outside.

    How to get

    It's on, so you should know the drill.

    • npm: npm install --save pragmatic-fp-ts
    • yarn: yarn add pragmatic-fp-ts

    Alternatively, include it in your webpage via jsdelivr:

    <script src=""></script>

    Breaking changes


    • functions no longer return Maybe monads as default
    • some function names changed
    • Maybe.match and Either.match no longer automatically catch errors, so they can be used as to throw when absolutely needed without leaving the monads' flow.
    • monads support transforming themselves when given a monad constructor

    Usability primer

    An elaborated readme will follow. Until then, you can see the auto generated docs on github.

    Differences to ramda

    • written in TS from the beginning with emphasis on inferring types over just being any
    • a very small set of functions is not implemented (at the time of writing, flavours of merge are the most noteworthy, although a pipe function exists)
    • very little function names differ
    • innerJoin behaves more like one would expect from an inner database join
    • compose and pipe use monadic-style infix composition instead of just accepting arguments. This allows for type-checked composition of an arbitrary number of functions in contrast to ramda's "list overloads" approach
    • return types look much cleaner and are arguably more readable by avoiding constructs like Curry4<Map<Filter<... and being more like <A,B>(value: A) => B[]
    • no support for fantasy-land objects

    Plans for the future

    • auto-infer even more types (although it's already quite good)
    • improve typing even more once TS implements variadic types
    • implement some more helpful functions found e.g. in lodash or Clojure
    • greater use of transducers
    • introduce lazyness, gradually change from type-overload hell to abstractions




    Although typing them is a bit of a PITA, transducers are a valuable addition for performance aware functional programmers. The first transducers implemented are:

    • map
    • filter
    • drop
    • take
    • flatMap
    • flatten

    which behave just like their non-transducing counterparts, as well as transformList which wraps the step of composing and applying a list of transducers over arrays.


    Mutables are for those situations where a clean functional solution is inconvenient to implement. They wrap a value and expose methods to mutate that value as well as a value accessor. After soon as the value is accessed for the first time, subsequent calls to the mutating functions will raise an Exception so we can still consume all the data safely.


    Some minor bugfixes, extended functionality of keys and values, some improved typings, most notably for the update function.


    Add cycle to create infinite sequence and a naive dummy infinite array type.


    Figured out how to setup webpack to create a browser bundle.


    Removed mori dependency. The runtime library is now completely self-contained. As a Clojure guy I relied on some of mori's functionality for the heavy lifting of deep get/set/update/equal operations.
    Sadly, to use mori's high performance algorithms, data had to be cast to mori data and back to JS-data after finishing, crippling performance within large data sets, so these functions are now completely re-implemented in "plain TypeScript" with a recursive, queue-based approach to path-getting.
    Deep equality implementation is based on epoberezkin/fast-deep-equal


    Added quick intersection testing functions.


    Implemented monadic Futures.


    • Deprecated the function name bind of monads, calling it _ instead. Although functional programmers should not have run into any problems with it, the name bind might confuse people coming from object oriented JavaScript programming, expecting function-this-argument-binding instead of monadic binding. The old name is still kept to keep older code from breaking too much. Composition is arguably easier to read this way.
    • Introduced flow, pipe, and compose, so now we should now be able to do anything with this lib we can do with ramda.
    • Still missing mergeXXX, as I still need to find performant ways to do so. I have a history with lodash's merge crippling one of my web apps' performance, and don't want anyone to run into similar issues, especially myself :D


    • ~100 new functions
    • some concept changes, see breaking changes


    • If you miss any FP construct, feel free to open an issue or PR. It's probably missing because I forgot to implement it/didn't need it yet. If it makes sense to me to have it here, I'll implement it.
    • Comments/PRs are very welcome, especially if you want to improve the docs.




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    • hellschwarz