Optic

Optic

new Optic()

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Mixes In:

Methods

binding(methodName, options) → {function}

DRYly bind a Function to the Object from which it was obtained

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See:

This method is a way to avoid duplicating code referencing an object within options.on when 1) obtaining the reference to the method's function, and 2) binding that method to the object from which it was accessed.

The return value of this method is always a Function; if the slot identified by this optic is not present in options.on or does not host a method named methodName, the trivial function (function () {} or equivalent) will be returned.

By default, the binding is lazy — the target of the lens within on is evaluated when the resulting Function is invoked (though on itself is bound in this call). To bind the resulting Function to its target immediately when this method is called, set options.bindNow to true.

Examples
const data = {question: "What is the ultimate answer?"};
const qStarts = lens('question').binding('startsWith', {on: data});
qStarts('What') // => true
data.question = "Why is a raven like a writing desk?";
qStarts('What') // => false
qStarts('Why') // => true
const data = {question: "What is the ultimate answer?"};
const qStarts = lens('question').binding('startsWith', {on: data, bindNow: true});
qStarts('What') // => true
data.question = "Why is a raven like a writing desk?";
qStarts('What') // => true (because qStarts bound to the target of the lens when `binding` was called)
Parameters:
Name Type Description
methodName string | symbol
options Object
Properties
Name Type Attributes Default Description
on *

The subject of the Function binding; becomes this for the result
bindNow boolean <optional>
 false

Bind to the Optic's target within on rather than binding to on
orThrow * <optional>

OptionalThrow if the slot referenced does not contain a Function; has precedence over or
or function <optional>

FallbackBindingResult, a Function to return if the slot referenced does not contain a Function
Returns:

A Function binding the methodName of the target of this optic to the target of this optic, or function() {} if no such function found

Type
function

get(subject, …tail) → {*}

Get the value of this slot within subject data

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If tail is given, then #get() is called on the result of getting this slot from subject, passing the spread of tail. This eliminates repeated use of .get in code. The chaining fails, returning undefined, if this slot in subject is not a lens-like object (as indicated by a truthy lens.isLens property).

Parameters:
Name Type Attributes Description
subject *

The data to query
tail * <repeatable>

Additional subjects for repeated application
Returns:

The value of this slot, or undefined if this slot is not present in subject

Type
*

(abstract) get_maybe(subject, …tail) → {Maybe.<*>}

Get a combination of present and value of this slot

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If tail is given and getting this slot from from subject yields a lens-like object (as indicated by a truthy lens.isLens property), then #get_maybe() is called on that lens, passing the spread of tail. If the value of this slot is not a lens, the result is an empty Object.

Parameters:
Name Type Attributes Description
subject *

The data to query
tail * <repeatable>

Additional subject for repeated application
Returns:

The value of the slot in a Maybe moand (Nothing if the slot is missing in subject)

Type
Maybe.<*>

getIterable(subject, optionsopt) → {Iterable.<*>}

Get the (iterable) value of this slot within some subject data

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If the slot does not exist within subject, this method returns an empty Array. If the slot within subject contains a non-iterable value, this method's behavior depends on orThrow. If orThrow is undefined, the behavior is the same as if the slot did not exist: an empty Array is returned. If orThrow is not undefined, orThrow is thrown; if orThrow is an Object, its noniterableValue property will be set to the slot's value before being thrown.

This method differs from Optic#get in that the returned value will always be iterable; thus, the return value of this method may safely be passed into any function expecting an iterable value. One example usage is constructing a Seq from the immutable package.

Strings, though iterable, are considered scalar values; if the targeted slot contains a string, the slot will be treated as non-iterable.

Parameters:
Name Type Attributes Description
subject *

The data to query
options Object <optional>
Properties
Name Type Attributes Description
orThrow * <optional>

OptionalThrow if the value of the slot exists but is not iterable
Returns:

An iterable of values from this slot (or an empty Array)

Type
Iterable.<*>

getting(subject, branches) → {T}

Conditionally evaluate functions depending on presence of slot

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The presence of the slot determines whether branches.then or branches.else is evaluated, with the result being returned from this method. If the indicated property of branches is missing, then undefined is returned.

Parameters:
Name Type Description
subject *

The input structured data
branches Object
Properties
Name Type Attributes Description
then function <optional>

Function evaluated if slot is present in subject
else function <optional>

Function evaluated if slot is absent from subject
Returns:

The value computed by branches.then or branches.else, or undefined

Type
T

present(subject) → {Boolean}

Test for the presence of this slot in subject data

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Parameters:
Name Type Description
subject *

The data to test
Returns:

Whether this slot is present in subject

Type
Boolean

setInClone(subject, newVal) → {T}

Clone subject, assigning the given value to this slot within the clone

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Where Optic#xformInClone_maybe is about applying some algorithmic transformation to the Maybe of this slot value, possibly setting or omitting this slot from the resulting clone, this method is about creating a clone returning the newVal when Optic#get of this instance is applied to it. This base implementation suffices when the xformInClone_maybe accepts as it's transform argument (i.e. second argument) a Function returning a Maybe of the slot value.

"Minimally changed" means that reference-copies are used wherever possible while leaving subject unchanged, and that setting the slot to the strict-equal value it already has results in returning subject.

Parameters:
Name Type Description
subject T

The input structured data
newVal *

The new value to inject into the slot identified by this lens within the returned clone
Returns:

A minimally changed clone of subject with newVal in this slot

Type
T

thence(…key) → {Lens|OpticArray}

Build a "deeper" lens/optic

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This method creates a new Optic that looks at finer detail than the Optic on which it was called. It either actually or effectively fuses a new Lens to the right of this optic, as with fuse.

Parameters:
Name Type Attributes Description
key * <repeatable>

A value to use in an application of subscripting (i.e. square bracket operator)
Returns:

An Optic that fuses this optic with a Lens looking at finer detail

Type
Lens | OpticArray

xformInClone(subject, fn, optsopt) → {T}

Clone the input, transforming the value within this slot with a function

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If this slot is missing in subject, fn will not be called unless addMissing is true, in which case fn will be called with undefined.

"Minimally changed" means that reference-copies are used wherever possible while leaving subject unchanged, and that setting the slot to the strict- equal value it already has results in returning subject.

Parameters:
Name Type Attributes Description
subject T

The input structured data
fn function

The function that transforms the slot value
opts Object <optional>
Properties
Name Type Default Description
addMissinng Boolean false

Whether to add the slot if missing in subject
Returns:

A minimally changed clone of subject with fn applied to the value in this slot

Type
T

xformInClone_maybe(subject, fn) → {T}

Clone the input, transforming or deleting the Maybe value of this slot with a function

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The concept of this method is of applying some clear algorithm to the content of the slot targeted by this Optic instance (in a Maybe monad, to cover the possibility of the slot itself not existing in subject) with the result returned in a Maybe monad (to allow for potential removal of the slot).

This implements what conceptually could, in Haskell, be described as:

Json -> (Maybe Json -> Maybe Json) -> Json

"Minimally changed" means that reference-copies are used wherever possible while leaving subject unchanged, and that setting the slot to the strict- equal value it already has results in returning subject.

Parameters:
Name Type Description
subject T

The input structured data
fn function

The function transforming the Maybe value of the slot
Returns:

A minimally changed clone of subject with this slot transformed per fn

Type
T

xformIterableInClone(subject, fn, optionsopt) → {T}

Clone the input, transforming the iterable value within this slot with a function

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If the slot does not exist within subject, fn is invoked on an empty Array. If the slot within subject contains a non-iterable value, this method's behavior depends on orThrow. If orThrow is undefined, the behavior is the same as if the slot did not exist: an empty Array is passed to fn. If orThrow is not undefined, orThrow is thrown; if orThrow is an Object, its noniterableValue property will be set to the slot's value before being thrown.

The primary differences between this method and Lens#xformInClone are that this method always passes an iterable value to fn and always calls fn even if the slot is missing or does not contain an iterable value (unless orThrow is given).

Strings, though iterable, are considered scalar values; if the targeted slot contains a string, the slot will be treated as non-iterable.

"Minimally changed" means that reference-copies are used wherever possible while leaving subject unchanged, and that setting the slot to the strict- equal value it already has results in returning subject.

Parameters:
Name Type Attributes Description
subject T

The input structured data
fn function

The function that transforms the (iterable) slot value
options Object <optional>
Properties
Name Type Attributes Description
orThrow * <optional>

OptionalThrow if the value of the slot exists but is not iterable
Returns:

A minimally changed clone of subject with the transformed value in this slot

Type
T