Cirru Extensible Data Notation

Data notation based on Cirru. Learnt from Clojure EDN.

EDN data is designed to be transferred across networks are strings. 2 functions involved:

parse-cirru-edn
format-cirru-edn

although items of a HashSet nad fields of a HashMap has no guarantees, they are being formatted with an given order in order that its returns are reasonably stable.

Liternals

For literals, if written in text syntax, we need to add do to make sure it's a line:

do nil

for a number:

do 1

for a symbol:

do 's

there's also "keyword", which is called "tag" since Calcit 0.7:

do :k

String escaping

for a string:

do |demo

or wrap with double quotes to support special characters like spaces:

do "|demo string"

or use a single double quote for mark strings:

do "\"demo string"

\n \t \" \\ are supported.

Data structures:

for a list:

[] 1 2 3

or nested list inside list:

[] 1 2
  [] 3 4

HashSet for unordered elements:

#{} :a :b :c

HashMap:

{}
  :a 1
  :b 2

also can be nested:

{}
  :a 1
  :c $ {}
    :d 3

Also a record:

%{} :A
  :a 1

Quotes

For quoted data, there's a special semantics for representing them, since that was neccessary for compact.cirru usage, where code lives inside a piece of data, marked as:

quote $ def a 1

at runtime, it's represented with tuples:

:: 'quote $ [] |def |a |1

which means you can eval:

$ cr -e "println $ format-cirru-edn $ :: 'quote $ [] |def |a |1"

quote $ def a 1

took 0.027ms: nil

and also:

$ cr -e 'parse-cirru-edn "|quote $ def a 1"'
took 0.011ms: (:: 'quote ([] |def |a |1))

This is not a generic solution, but tuple is a special data structure in Calcit and can be used for marking up different types of data.

Buffers

there's a special syntax for representing buffers in EDN using pairs of Hex digits as u8:

buf 03 55 77 ff 00

which corresponds to:

&buffer 0x03 0x55 0x77 0xff 0x00

Comments

Comment expressions are started with ;. They are evaluated into nothing, but not available anywhere, at least not available at head or inside a pair.

Some usages:

[] 1 2 3 (; comment) 4 (; comment)

{}
  ; comment
  :a 1

Also notice that comments should also obey Cirru syntax. It's comments inside the syntax tree, rather than in parser.

Calcit Guide