ℒ Data Notation
EllDN is the ℒ Data Notation, pronounced /ˈɛldən/ ("EL-dən"). It is a superset of JSON, adding lists, symbols, keywords, types, and generalized typed object instances.
Commas are considered whitespace in EllDN, so the following are equivalent:
[1, 2, 3]
[1 2 3]
Symbols are tokens that are not valid numbers.
The JSON reserved values null, true, and false are symbols that are defined to have the expected meaning.
EllDN also defines a keyword to be a token ending with a colon (:). A type is a symbol surrounded by
angle brackets, i.e. <string>.
Inside a struct, a colon that is not part of a keyword is treated as whitespace. So for example the following are equivalent:
{"x": 23, "y": 57}
{"x" 23, "y" 57}
{"x" 23 "y" 57}
Symbols, and more commonly, keywords, are useful as keys in an struct (a JSON object):
{x 23 y: 57}
This has the symbol x as a key, and a keyword y: as a key. It is valuable to distinguish between symbols and keywords
when using EllDN as language source like the Ell language, as the two are interpreted
differently.
Some more examples:
() - an empty list
true - the true value
foo - some symbol
foo? - another symbol
foo! - also a valid symbol
foo: - a keyword
<foo> - a type
[1, 2, 3] - a vector (JSON array) of 3 values
[1 2 3] - an equivalent vector
(1 2 3) - a list of 3 elements
(1, 2, 3) - same thing (commas are optional)
{"foo": 2, "bar": 3} - a regular JSON object
{foo: 2, bar: 3} - an object using keywords as keys
{foo: 2 bar: 3} - commas are optional here, too
{list-items: (1 2 3) vector-items: [1 2 3]} - an object with list and vector values
(<string> <number>) - a list of types
#<point>{x: 23 y: 57} - an object instance of type <point>, with a structured value.
Valid JSON is readable as EllDN, although not all EllDN can be expressed as JSON.
For the syntax, see the Syntax Diagrams, generated from EBNF.