JSON

type Error

Why a document could not be parsed. Every variant carries the position in the input where the parser stopped, so a caller can point at the problem.

JSON.parse("[1, 2")    # => Error(UnexpectedEnd(5))
JSON.parse("// c\n1")  # => Error(UnexpectedCharacter("/", 0))

Variants

• UnexpectedCharacter(String, Integer)
• UnexpectedEnd(Integer)
• InvalidLiteral(String, Integer)
• InvalidNumber(String, Integer)
• InvalidEscape(String, Integer)
• InvalidUnicodeEscape(String, Integer)
• UnterminatedComment(Integer)
• TrailingInput(Integer)
• UnknownOption(Atom)

function parse

Parses a JSON document, strictly.

The whole text must be one JSON value with nothing after it: trailing input is TrailingInput, not a silently ignored tail. Objects come back as maps with atom keys, arrays as lists, null as None.

parse(text) : String -> Result<Any, Error>
parse(text) : String -> {Atom: Bool} -> Result<Any, Error>

Parameters

text String

the JSON document

Returns: Result<Any, Error> — the parsed value, or why it failed

Examples

JSON.parse("{\"a\": 1, \"b\": [true, null, 2.5]}")
# => Ok({ a: 1, b: [true, None, 2.5] })
JSON.parse("[1, 2")   # => Error(UnexpectedEnd(5))

Reading a config file

match JSON.parse(FS.File.read("config.json").or("")) do
  Ok(config) => IO.printLine(config)
  Error(e)   => IO.printError("config.json is not valid JSON: ${e}")
end

function stringify

Renders a Kex value as strict JSON text.

Maps become objects, lists become arrays, None becomes null, and strings are escaped. A map written with atom keys (the usual Kex spelling) renders with those names as strings, so { name: "Ada" } becomes {"name":"Ada"}. Object keys come out in canonical key order.

Anything the encoder does not recognise renders as null rather than failing, so this never raises.

stringify(value) : Any -> String

Parameters

value Any

the value to render

Returns: String — the JSON text

Examples

JSON.stringify({ name: "Ada", n: 1, ok: true })
# => '{"n":1,"name":"Ada","ok":true}'
JSON.stringify([1, 2, 3])
# => '[1,2,3]'

Writing a JSON file

FS.File.write("out.json", JSON.stringify(report))

A round trip

JSON.parse(JSON.stringify({ a: 1 }))   # => Ok({ a: 1 })