<a id="partial-lenses"></a> ≡ ▶ Partial Lenses ·

Lenses are basically an abstraction for simultaneously specifying operations to update and query immutable data structures. Lenses are highly composable and can be efficient. This library provides a rich collection of partial isomorphisms, lenses, and traversals, collectively known as optics, for manipulating JSON and users can write new optics for manipulating non-JSON objects, such as Immutable.js collections. A partial lens can view optional data, insert new data, update existing data and remove existing data and can, for example, provide defaults and maintain required data structure parts. Try Lenses!

<a id="contents"></a> ≡ ▶ Contents

• Tutorial
  • Getting started
  • A partial lens to access title texts
    • Querying data
      • Missing data can be expected
    • Updating data
    • Inserting data
    • Removing data
    • Exercises
  • Shorthands
  • Systematic decomposition
  • Manipulating multiple items
  • Next steps
• The why of optics
• Reference
  • Stable subset
  • Additional libraries
  • Optics
    • On partiality
    • On indexing
    • On immutability
    • On composability
    • On lens laws
      • Myth: Partial Lenses are not lawful
    • Operations on optics
      • L.assign(optic, object, maybeData) ~> maybeData <small>^v11.13.0</small>
      • L.disperse(optic, [...maybeValues], maybeData) ~> maybeData <small>^v14.6.0</small>
      • L.modify(optic, (maybeValue, index) => maybeValue, maybeData) ~> maybeData <small>^v2.2.0</small>
      • L.modifyAsync(optic, (maybeValue, index) => maybeValuePromise, maybeData) ~> maybeDataPromise <small>^v13.12.0</small>
      • L.remove(optic, maybeData) ~> maybeData <small>^v2.0.0</small>
      • L.set(optic, maybeValue, maybeData) ~> maybeData <small>^v1.0.0</small>
      • L.traverse(algebra, (maybeValue, index) => operation, optic, maybeData) ~> operation <small>^v10.0.0</small>
    • Nesting
      • L.compose(...optics) ~> optic or [...optics] <small>^v1.0.0</small>
      • L.flat(...optics) ~> optic <small>^v13.6.0</small>
    • Recursing
      • L.lazy(optic => optic) ~> optic <small>^v5.1.0</small>
    • Adapting
      • L.choices(optic, ...optics) ~> optic <small>^v11.10.0</small>
      • L.choose((maybeValue, index) => optic) ~> optic <small>^v1.0.0</small>
      • <a href="#l-cond" title="L.cond: (...[(Maybe s, Index) -&gt; Boolean, POptic s a][, [POptic s a]]) -&gt; POptic s a"><code>L.cond(...[(maybeValue, index) => testable, consequentOptic][, [alternativeOptic]]) ~> optic</code></a> <small>^v13.1.0</small>
      • <a href="#l-condof" title="L.condOf: (PTraversal s c, ...[(Maybe c, Index) -&gt; Boolean, POptic s a][, [POptic s a]]) -&gt; POptic s a"><code>L.condOf(traversal, ...[(maybeValue, index) => testable, consequentOptic][, [alternativeOptic]]) ~> optic</code></a> <small>^v13.5.0</small>
      • L.ifElse((maybeValue, index) => testable, optic, optic) ~> optic <small>^v13.1.0</small>
      • L.orElse(backupOptic, primaryOptic) ~> optic <small>^v2.1.0</small>
    • Indices
      • L.joinIx(optic) ~> optic <small>^v13.15.0</small>
      • L.mapIx((index, maybeValue) => index) ~> optic <small>^v13.15.0</small>
      • L.reIx(optic) ~> optic <small>^v14.10.0</small>
      • L.setIx(index) ~> optic <small>^v13.15.0</small>
      • L.skipIx(optic) ~> optic <small>^v13.15.0</small>
      • L.tieIx((innerIndex, outerIndex) => index, optic) ~> optic <small>^v13.15.0</small>
    • Debugging
      • L.getLog(lens, maybeData) ~> maybeValue <small>^v13.14.0</small>
      • L.log(...labels) ~> optic <small>^v3.2.0</small>
    • Internals
      • L.Identity ~> Monad <small>^v13.7.0</small>
      • L.IdentityAsync ~> Monadish <small>^v13.12.0</small>
      • L.Select ~> Applicative <small>^v14.0.0</small>
      • L.toFunction(optic) ~> optic <small>^v7.0.0</small>
  • Transforms
    • Operations on transforms
      • L.transform(optic, maybeData) ~> maybeData <small>^v11.7.0</small>
      • L.transformAsync(optic, maybeData) ~> maybeDataPromise <small>^v13.12.0</small>
    • Sequencing
      • L.seq(...transforms) ~> transform <small>^v9.4.0</small>
    • Transforming
      • L.appendOp(value) ~> traversal <small>^v14.14.0</small>
      • L.assignOp(object) ~> traversal <small>^v11.13.0</small>
      • L.modifyOp((maybeValue, index) => maybeValue) ~> traversal <small>^v11.7.0</small>
      • L.prependOp(value) ~> traversal <small>^v14.14.0</small>
      • L.removeOp ~> traversal <small>^v11.7.0</small>
      • [L.setOp(maybeValue) ~> traversal](#l-setop 'L.setOp: Maybe