ExpressionJSON (.json)

Import and Export support ExpressionJSON.
ExpressionJSON provides lossless round-tripping of Wolfram Language expressions to and from JSON.
By default, Import and Export use the "JSON" format for files ending in .json, rather than the "ExpressionJSON" format.

Background & Context

Import["file","ExpressionJSON"] imports a file that uses the ExpressionJSON format, producing an ordinary Wolfram Language expression.
Export["file",expr,"ExpressionJSON"] exports an arbitrary expression to ExpressionJSON.
Elements of expressions are represented as follows in ExpressionJSON:

	"string"	"'string'" (UTF-8, with JSON escaping)
	True, False	true, false
	Null	null
	symbol	"symbol" (UTF-8)
	f[e₁,e₂,…,opt₁val₁,…]	["f",e₁,e₂,…,["Rule",opt₁,val₁],…]

Machine integers are represented literally. Larger integers are represented as "digits".
Machine-precision numbers are represented as JSON numbers using e notation.
Arbitrary-precision numbers are by default given as "number", where number is the InputForm representation of the number.

	"Elements"	list of elements and options available in this file
	"Rules"	full list of rules for each element and option
	"Options"	list of rules for options, properties, and settings

"Compact"	False	whether to omit line breaks and tabs
"NullSymbols"	{}	a list of symbols to represent as JSON null
"PrecisionHandling"	True	whether to allow bignums or issue a message

Import a JSON list:

Import a String:

Import a Quantity:

Export an expression to a JSON string:

Export a list while converting None to JSON null:

Export a list of numbers of arbitrary precision:

Export a list of numbers and issue an error if any of them is not a machine-precision number:

Control the output format with "Compact" to limit indentation:

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