rontolisp:json-stringify

(rontolisp:json-stringify value)

Serializes a Lisp value into a JSON document string, following the defaults of the com.inuoe.jzon library and inverting rontolisp:json-parse: a hash table becomes an object, a vector or list an array, and nil, t and the symbol null become false, true and null. It is a lightweight subset of jzon, so a program can switch to jzon without changing shape.

Switch to com.inuoe.jzon when you outgrow the subset: for its richer features (pretty-printing, a streaming writer, a :replacer, custom serialization), or to make the JSON code portable to other Common Lisp implementations — com.inuoe.jzon is a standard library, while rontolisp:json-* runs only on rontolisp.

Value mapping

Lisp	JSON
`nil`	`false`
`t`	`true`
the symbol `null`	`null`
integer, float	number
ratio	number (converted with `float`)
string	string (quote, backslash and control characters are escaped)
vector, list	array
hash table	object (a symbol key is down-cased unless it has a lower-case letter)
CLOS instance (`standard-object`)	object (each slot name → its value, in definition order)
keyword, symbol, character	string

Anything else (functions, streams, multidimensional arrays) signals an error.

A hash table and a CLOS instance both serialize as objects, so there are two ways to build one — a hash table (often via rontolisp:plist-hash-table) for dynamic keys, and a class for a fixed shape. A slot may itself hold a hash table (a nested object), a list or vector (an array), or another instance:

A value parsed from JSON round-trips structurally:

Limitations

nil serializes as false and the empty list is nil, so use #() (an empty vector) for an empty array and an empty hash table for an empty object {}.
A list is always an array — build a hash table for a JSON object (jzon dropped alist/plist detection, and so does this subset). rontolisp:plist-hash-table turns a keyword property list, and rontolisp:alist-hash-table an association list, into that hash table.
Hash-table key order in the output is backend-specific (unspecified), like maphash.
Non-ASCII characters are emitted verbatim (never \uXXXX-escaped), which is valid JSON.
On the WASM backends a float with magnitude 2³¹ or larger cannot be serialized (the float formatter traps); see the WASM guide.

Backend support

Works on every backend and in every WASM mode (Preview 1 included), like rontolisp:json-parse: the serializer is written in rontolisp itself and is compiled into the program when used.