Class IdentitySelector

Always returns [[Absent]] because a Value can't be a Field, so it can't have a key component.

Returns the number of members contained in this Value, if this Value is a [[Record]]; otherwise returns 0 if this Value is not a Record.

Returns the key string of the first member of this Value, if this Value is a [[Record]], and its first member is an [[Attr]]; otherwise returns undefined if this Value is not a Record, or if this Value is a Record whose first member is not an Attr.

Used to concisely get the name of the discriminating attribute of a structure. The tag can be used to discern the nominal type of a polymorphic structure, similar to an XML element tag.

Returns the [[Value.flattened flattened]] members of this Value after all attributes have been removed, if this Value is a [[Record]]; otherwise returns this if this Value is not a Record.

Used to concisely get the scalar value of an attributed structure. An attributed structure is a Record with one or more attributes that modify one or more other members.

Returns the [[Record.flattened flattened]] [[Value.tail tail]] of this Value. Used to recursively deconstruct a structure, terminating with its last Value, rather than a unary Record containing its last value, if the structure ends with a Value member.

Converts this Value into a boolean value, if possible; otherwise returns undefined if this Value can't be converted into a boolean value.

Converts this Value into a boolean value, if possible; otherwise returns orElse if this Value can't be converted into a boolean value.

Returns the sole member of this Value, if this Value is a [[Record]] with exactly one member, and its member is a Value; returns [[Extant]] if this Value is an empty Record; otherwise returns this if this Value is a Record with more than one member, or if this Value is a not a Record.

Used to convert a unary Record into its member Value. Facilitates writing code that treats a unary Record equivalently to a bare Value.

Returns the last [[Field]] member of this Value whose key is equal to the given key; returns undefined if this Value is not a [[Record]], or if this Value is a Record, but has no Field member with a key equal to the given key.

Returns the value of the last [[Slot]] member of this Value whose key is equal to the given key; returns [[Absent]] if this Value is not a [[Record]], or if this Value is a Record, but has no Slot member with a key equal to the given key.

Returns true if this Value is a [[Record]] that has a [[Field]] member with a key that is equal to the given key; otherwise returns false if this Value is not a Record, or if this Value is a Record, but has no Field member with a key equal to the given key.

Returns the first member of this Value, if this Value is a non-empty [[Record]]; otherwise returns [[Absent]].

Returns the value of the first member of this Value, if this Value is a Record, and its first member is an [[Attr]] whose key string is equal to tag; otherwise returns [[Absent]] if this Value is not a Record, or if this Value is a Record whose first member is not an Attr, or if this Value is a Record whose first member is an Attr whose key does not equal the tag.

Used to conditionally get the value of the head Attr of a structure, if and only if the key string of the head Attr is equal to the tag. Can be used to check if a structure might conform to a nominal type named tag, while simultaneously getting the value of the tag attribute.

Returns the [[Value.unflattened unflattened]] [[Value.header header]] of this Value, if this Value is a [[Record]], and its first member is an [[Attr]] whose key string is equal to tag; otherwise returns undefined.

The headers of the tag attribute of a structure are like the attributes of an XML element tag; through unlike an XML element, tag attribute headers are not limited to string keys and values.

Returns true if this Item always [[Item.evaluate evaluates]] to the same Item.

Returns true if this Value is not [[Absent]].

Returns true if this Value is not one of: an empty Record, False, Extant, or Absent.

Returns true if this Value is neither [[Extant]] nor [[Absent]].

Converts this Value into a number value, if possible; otherwise returns undefined if this Value can't be converted into a number value.

Converts this Value into a number value, if possible; otherwise returns orElse if this Value can't be converted into a number value.

Converts this Value into a string value, if possible; otherwise returns undefined if this Value can't be converted into a string value.

Converts this Value into a string value, if possible; otherwise returns orElse if this Value can't be converted into a string value.

Returns a view of all but the first member of this Value, if this Value is a non-empty [[Record]]; otherwise returns an empty Record if this Value is not a Record, of if this Value is itself an empty Record.

Always returns this because every Value is its own value component.

Returns this if this Value is a [[Record]]; returns a Record containing just this Value, if this Value is [[Value.isDistinct distinct]]; otherwise returns an empty Record if this Value is [[Extant]] or [[Absent]]. Facilitates writing code that treats a bare Value equivalently to a unary Record.