test.md

Data serialization formats

Comparison of selected data serialization formats.

• JSON - ECMA-404
• EDN - github.com/edn-format/edn
• CLJ - clojure.org/reader

Whitespace

	JSON	EDN	CLJ
whitespace character	U+0009 (tab) U+000A (newline) U+000D (return) and U+0020 (space)	⚠️ specs does not specify	whitespace chars, explicitly mentions just ,
delimiters	whitespaces, all structural ({ } : , [ ]) and literal (true false null) tokens	whitespaces and [ ] { } ( ) ( ⚠️ additional delimiters not mentioned in specs " \ ;)	[ ] { } ( ) " \ ; @ ^ ` ~ (:warning: no explicit mention in specs)

Null

	JSON	EDN	CLJ
null literal	null	nil	nil

Booleans

	JSON	EDN	CLJ
true literal	true	true	true
false literal	false	false	false

Characters

	JSON	EDN	CLJ
syntax	NONE ❌	\X	\X
special characters	n/a	\newline \tab \return \space	\newline \tab \return \space \backspace \formfeed
unicode escapes	n/a	\uNNNN	\uNNNN
octal escapes	n/a	NO ❌	\o0 to \o377

Strings

	JSON	EDN	CLJ
syntax	wrapped in "	wrapped in "	wrapped in "
may span multiple lines	NO ❌	YES	YES
characters which must be escaped	" \ and control characters (U+0000 to U+001F)	" \	" \
escape characters	\" \\ \/ \b \f \n \r \t	\" \\ \n \r \t	\" \\ \' \b \f \n \r \t
unicode escapes	\uNNNN	NO, not mentioned in specs ❌	\uNNNN
octal escapes	NO ❌	NO ❌	\0 to \377

Integers

	JSON	EDN	CLJ
varbitrary precision indicator	NO ❌	N suffix	N suffix
vvalid signs	-	- +	- +
-0 is valid	YES	YES	YES
decimal integer	YES	YES	YES
custom radix	NO ❌	NO ❌	NNrNNNNN
hexa integer	NO ❌	NO ❌	0xNNNNN, but undocumented ⚠️
octal integer	NO ❌	NO ❌	0NNN, but undocumented ⚠️

Non-integral numbers

	JSON	EDN	CLJ
ratios	NO ❌	NO ❌	NN/NN
decimals	NO ❌	M suffix	M suffix
floats	YES	YES	YES
valid signs	-	- +	- +

Identifiers

	JSON	EDN	CLJ
symbols	NO ❌	YES	YES
symbol start character	n/a	alphabetic, + - . followed by non-numeric symbol character, * ! _ ? $ % & = < > (/ is special, see below)	alphabetic, + - * ! _ ? (/ and . are special, see below), ( ⚠️ specs does not mention $ = < > % &)
symbol character	n/a	alphanumeric, + - . * ! _ ? $ % & = < > : #	alphanumeric, + - * ! _ ? (. / and : are special, see below), ( ⚠️ specs does not mention $ = < > % & # ')
special symbol character	n/a	/, used alone or in following combinations foo/bar (:warning: In my opinion specs does not allow foo// combination, see this ticket). First character after slash must follow rule for symbol start character	/, used alone or in following combinations foo/bar foo// (:warning: latter combination is undocumented). ., used as prefix or suffix is reserved to Clojure, used inside symbol divides namespace or package names. : can be used inside symbol, used as suffix is reserved to Clojure (currently it produces an error). (:warning: undocumented restrictions: symbol can not contain ::, namespace part can not end with :, first character after slash must follow rule for symbol start character)
keyword	NO ❌	prefixed with :	prefixed with :
keyword character	n/a	alphanumeric, + - . * ! _ ? $ % & = < > : #	alphanumeric, + - * ! _ ? (. / and : are special, see below), ( ⚠️ specs does not mention $ = < > % & # ')
keyword invalid second character	n/a	:	none special
special keyword character	n/a	/, used in following combinations :foo// :foo/bar. First character after slash must follow rule for symbol start character	/, used in following combinations :foo/bar :foo// (:warning: latter combination is undocumented). : used as second character resolves keyword in the current namespace, used as suffix is reserved to Clojure (currently it produces an error). (:warning: undocumented restrictions: keyword can not contain :: other than as a prefix, namespace part can not end with :, first character after slash must follow rule for symbol start character) Specs also say that keywords cannot contain '.' ( ⚠️ restriction meant probably only for the name part of the keyword) or name classes.

Collections

	JSON	EDN	CLJ
list	NO ❌	(a b c)	(a b c)
vector	[a, b, c]	[a b c]	[a b c]
set	NO ❌	#{a b c} items are unique	#{a b c} items are unique
map	{string1 : val1, string2 : val2]	{key1 val1 key2 val2} keys are unique	{key1 val1 key2 val2} keys are unique

Special

	JSON	EDN	CLJ
comments	NO ❌	; till the end of the line	; till the end of the line
discard	NO ❌	#_ discards next read object	#_ discards next read object
tagged literal	NO ❌	# followed immediately by a symbol starting with an alphabetic character	# followed immediately by a symbol starting with an alphabetic character
builtin tags	n/a	#inst #uuid	#inst #uuid, deftypes, defrecords and java classes constructors
regular expressions	NO ❌	NO ❌	#"pattern"
macros	NO ❌	NO ❌	' (quote), @ (deref), ^ (metadata), #' (var quote), #(% %n %&) (anonymous function), ` (syntax quote), ~ (unquote), ~@ (unquote splicing). (:warning: undocumented macros #= #! #< and deprecated #^)