Data serialization formats

Comparison of selected data serialization formats.

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

Whitespace

x	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 ,	⚠️ 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

x	JSON	EDN	CLJ
null literal	null	nil	nil

Booleans

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

Characters

x	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

x	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

x	JSON	EDN	CLJ
arbitrary precision indicator	NO ❌	N suffix	N suffix
valid 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

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

Identifiers

x	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

x	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

x	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 #^)