The `json()` function parses the given string value as JSON.

Throws an exception if the given input value is not a string.
Throws an exception if the given input string cannot be parsed as JSON.

Returns the resulting value.

-- Testcase --
{%
	print(join("\n", [
		json("null"),
		json("true"),
		json("false"),
		json("123"),
		json("456.7890000"),
		json("-1.4E10"),
		json("1e309"),
		json('"A string \u2600"'),
		json("[ 1, 2, 3 ]"),
		json('{ "test": [ 1, 2, 3 ] }'),

		// surrounding white space is ignored
		json('    [ 1, 2, 3 ]    ')
	]), "\n");
%}
-- End --

-- Expect stdout --
null
true
false
123
456.789
-14000000000
Infinity
A string ☀
[ 1, 2, 3 ]
{ "test": [ 1, 2, 3 ] }
[ 1, 2, 3 ]
-- End --


Passing a non-string value throws an exception.

-- Testcase --
{%
	json(true);
%}
-- End --

-- Expect stderr --
Type error: Passed value is neither a string nor an object
In line 2, byte 11:

 `    json(true);`
  Near here ---^


-- End --


Unparseable JSON throws exceptions.

-- Testcase --
{%
	json('[ "incomplete", "array" ');
%}
-- End --

-- Expect stderr --
Syntax error: Failed to parse JSON string: unexpected end of data
In line 2, byte 33:

 `    json('[ "incomplete", "array" ');`
  Near here -------------------------^


-- End --

-- Testcase --
{%
	json('invalid syntax');
%}
-- End --

-- Expect stderr --
Syntax error: Failed to parse JSON string: unexpected character
In line 2, byte 23:

 `    json('invalid syntax');`
  Near here ---------------^


-- End --

-- Testcase --
{%
	json('[] trailing garbage');
%}
-- End --

-- Expect stderr --
Syntax error: Trailing garbage after JSON data
In line 2, byte 28:

 `    json('[] trailing garbage');`
  Near here --------------------^


-- End --


Additionally, `json()` accepts objects implementing a read method as input.
During JSON parsing, the read method is repeatedly invoked with a buffer size
hint as sole argument. The return value of the read method is converted to a
string if needed and passed on to the JSON parser. A `null` or an empty string
return value is treated as EOF, ending the parse process.

-- Testcase --
{%
	let fs = require("fs");

	// parse JSON from open file handle
	printf("%.J\n",
		json(fs.open("files/test.json"))
	);
%}
-- End --

-- Expect stdout --
{
	"hello": "world"
}
-- End --

-- File test.json --
{"hello":"world"}
-- End --


The `json()` function is able to parse JSON from any object providing a `read()`
method that incrementally yields JSON source data.

-- Testcase --
{%
	let parts = [
		'{"some"',
		':',
		'"object"',
		', ',
		'"etc."',
		':',
		!0,  // this is stringified to "true"
		'}'
	];

	let producer = {
		read: function(size) {
			return shift(parts);
		}
	};

	// parse JSON from producer object
	printf("%.J\n",
		json(producer)
	);
%}
-- End --

-- Expect stdout --
{
	"some": "object",
	"etc.": true
}
-- End --


Passing objects or resources not providing a `read()` method yields an exception.

-- Testcase --
{%
	json({});
%}
-- End --

-- Expect stderr --
Type error: Input object does not implement read() method
In line 2, byte 9:

 `    json({});`
  Near here -^


-- End --


Exceptions triggered by the `read()` method are properly forwarded.

-- Testcase --
{%
	json({
		read: function() {
			die("Exception in read()");
		}
	});
%}
-- End --

-- Expect stderr --
Exception in read()
In [anonymous function](), line 4, byte 29:
  called from function json ([C])
  called from anonymous function ([stdin]:6:3)

 `            die("Exception in read()");`
  Near here ---------------------------^


-- End --


EOF stops parsing and does not lead to further `read()` invocations.

-- Testcase --
{%
	let parts = [
		'["some",',
		'"JSON array",',
		'true,false,1,2,3',
		']',
		'',                  // empty string treated as EOF
		'{"some":',          // this is not reached in the first pass
		'"object"}',
		null,		         // null treated as EOF
		'"test ',            // this is not reached in the second pass
		'value"'
	];

	let producer = { read: () => shift(parts) };

	printf("%.J\n", [
		json(producer),
		json(producer),
		json(producer)
	]);
%}
-- End --

-- Expect stdout --
[
	[
		"some",
		"JSON array",
		true,
		false,
		1,
		2,
		3
	],
	{
		"some": "object"
	},
	"test value"
]
-- End --