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 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 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 unflattened 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 Value is not Absent.
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 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.
Always returns this because every Value is its own value component.
Always returns Absent because a
Valuecan't be aField, so it can't have a key component.