Optika

Optics: modular data access

Getting Started

Install the module with: npm install optika

Synopsis

var o = require("optika");
 
var value = {
  foo: [
    { bar: 2, baz: 3 },
    { bar: 4, baz: 5 },
  ]
};
 
// [2, 4]
o.key("foo").traversed().key("bar").arrayOf(value);
 
// { foo: [ { bar: 9, baz: 3 }, { bar: 11, baz: 5 } ] }
o.key("foo").traversed().key("bar").over(value, function (x) {
  return x + 7;
});

Motivation

Immutable.js is great! But working with immutable containers & nested records is un-easy:

return data.update("months", months =>
  months.map(month =>
    month.update("days", days =>
      days.map(day => injectAuxData(day, auxiliaryData))
    )
  )
);

The updateIn isn't powerful enough to make the drilling less boilerplaty (and less error-prone).

If you are a Haskell programmer, you might know that lenses are a solution to this problem:

data_ & months . traversed . days . traversed %~ \day ->
  injectAuxData day auxData
 
-- or without operators:
over
  (months . traversed . days . traversed)
  (\day -> injectAuxData day auxData)
  data_

And with this library you can write similar code in JavaScript:

o.imkey("months").traversed().imkey("days").traversed().over(data, day =>
  injectAuxData(day, auxData)
);

Documentation

There is small amount of run-time validation. For example, if you try to set over Getter, the exception will be thrown:

o.key("foo").to(function (x) { return x[0]; }).set(value, 42);
// throws: Trying to run Traversal operation via Getter

Operations

• get(this: Getter<S,A>, value: S): A

• set(this: Traversal<S,T,A,B>, value: S, b: B): T

• over(this: Traversal<S,T,A,B>, value: S, f: A => B): T

• review(this: Prism<S,T,A,B>, value: B): T

• review(this: Iso<S,T,A,B>, value: B): T

  Construct value thru Prism or Iso.

• `affineView(this: Affine<S,T,A,B>, def: A): A

  For operation working with Fold, see firstOf.

• reduceOf(this: Fold<S,T,A,B>, value: S, init: I, combine: (I, A) => I): I

  Fold starting with initial value init, and combining results with combine, in the this Fold's order.

• arrayOf(this: Fold<S,T,A,B>, value: S): Array<A>

• sumOf(this: Fold<S,T,number,B>, value: S): number

Constructors

• lens(getter: S => A, setter: (S, B) => T): Lens<S,T,A,B>

• traversed(): Traversal<F<A>,F<B>,A,B>

  Creates traversal for everything with .map and .forEach.

• to(f: S => A): Getter<S,A>

Convenient optics

• key(K: keyof (S & T)): Lens<S,T,S[K],T[K]>

  Works for plain-old-javascriot-objects, i.e. POJOs :)

• idx(i: number)): Lens<Array<A>,Array<A>,A,A>

• imkey(K: keyof (S & T)): Lens<Record<S>,Record<T>,S[K],T[K]>

  Works with everyting supporting .get and .set, e.g. Immutable.

• imidx(i: number)): Lens<List<A>,List<A>,A,A>

  Works with everyting supporting .get and .set, e.g. Immutable.

  Note: doesn't perform bounds check.

• filtered(pred: A => boolean): Prism<A,A,A',A'>

Note: The predicate is checked when the value is injected (via Traversal) or constructed via Prism.

• safeFiltered(pred: A => boolean): Prism<A,A,A',A'>

Like filtered but predicate is checked on construction.

Internals

Functions which you probably never need to use directly.

.o(this: Optic<S,T,A,B>, other: Optic<A,B,U,V>): Optic<S,T,U,V>

Compose two optics.

.run(this: Optic<S,T,A,B>, p: Profunctor<A,B>): Profunctor<S,T>

Contributing

• README.md is generated from the source with ljs, say make literate.
• optika.standalone.js is also generated by the build process
• Before creating a pull request run make test, yet travis will do it for you.

Release History

• 0.0.2 — 2017-04-01 — Neglect for speedups
• 0.0.1 — 2017-03-24 — More features
• 0.0.0 — 2017-03-22 — Initial preview

Implementation details

• pair is represented as two-element array: Pair<A,B> = [A,B].
• Either is represtented by [boolean, A | B], where false and true reprsent whether the value is Left or Right respectively.
• Maybe is encoded as the value + some unique value nothing can equal to (think: Symbol).
• See Compiling lenses for ideas behind Neglect.

Related work

JavaScript

• partial.lenses
• ramda-lens
• flunc-optics

The MIT License (MIT)

Copyright (c) 2017 Oleg Grenrus

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.