Kenpali JSON Specification
Literals
A literal expression has the form {"literal": <value>}. The value can be null, true, false, or any valid JSON string or number.
Examples:
# Literal null
{"literal": null}
>> null# Literal false
{"literal": false}
>> false# Literal true
{"literal": true}
>> true# Literal number
{"literal": 1}
>> 1# Literal string
{"literal": "foobar"}
>> "foobar"Names
# Binding a name
{
"defining": [["foo", {"literal": 42}]],
"result": {"name": "foo"}
}
>> 42# Binding multiple names
{
"defining": [
["bar", {"literal": 42}],
["baz", {"name": "bar"}],
["foo", {"name": "baz"}]
],
"result": {"name": "foo"}
}
>> 42# Name used before assignment
{
"defining": [
["foo", {"name": "baz"}],
["bar", {"literal": 42}],
["baz", {"name": "bar"}]
],
"result": {"name": "foo"}
}
!! nameUsedBeforeAssignment {"name": "baz"}# Name declared more than once in the same scope
{
"defining": [
["foo", {"literal": 42}],
["foo", {"literal": 97}]
],
"result": {"name": "foo"}
}
!! duplicateName {"name": "foo"}# Scope
{
"defining": [
[
"foo",
{
"defining": [
["bar", {"literal": 42}]
],
"result": {"literal": null}
}
]
],
"result": {"name": "bar"}
}
!! nameNotDefined {"name": "bar"}# A name from an enclosing scope
{
"defining": [
["foo", {"literal": 42}]
],
"result": {
"defining": [
["bar", {"literal": 73}]
],
"result": {"name": "foo"}
}
}
>> 42# Shadowing
{
"defining": [
["foo", {"literal": 42}]
],
"result": {
"defining": [
["foo", {"literal": 73}]
],
"result": {"name": "foo"}
}
}
>> 73# Expression statements
{
"defining": [
[null, {"literal": 42}]
],
"result": {"literal": 73}
}
>> 73Arrays
# Empty array
{"array": []}
>> []# Array of literals
{"array": [{"literal": 1}, {"literal": 2}, {"literal": 3}]}
>> [1, 2, 3]# Array with elements of mixed types
{"array": [{"literal": null}, {"literal": 1}, {"literal": "foo"}]}
>> [null, 1, "foo"]# Nested arrays
{"array": [{"array": [{"literal": 1}]}]}
>> [[1]]# Array containing an expression to evaluate
{
"defining": [["foo", {"literal": 42}]],
"result": {"array": [{"name": "foo"}]}
}
>> [42]# Array with spread
{
"array": [
{"literal": 42},
{
"spread": {
"array": [
{"literal": 1},
{"literal": 2},
{"literal": 3}
]
}
},
{"literal": 97}
]
}
>> [42, 1, 2, 3, 97]# Array destructuring
{
"defining": [
[
{"arrayPattern": ["foo", "bar"]},
{
"array": [
{"literal": 42},
{"literal": 97}
]
}
]
],
"result": {
"array": [
{"name": "bar"},
{"name": "bar"},
{"name": "foo"}
]
}
}
>> [97, 97, 42]# Array destructuring with rest
{
"defining": [
[
{"arrayPattern": ["foo", {"rest": "bar"}, "baz"]},
{
"array": [
{"literal": 42},
{"literal": 1},
{"literal": 2},
{"literal": 3},
{"literal": 97}
]
}
]
],
"result": {
"array": [
{"name": "baz"},
{"name": "foo"},
{"name": "bar"}
]
}
}
>> [97, 42, [1, 2, 3]]Objects
# Empty object
{"object": []}
>> {}# Object with literal values
{
"object": [
["foo", {"literal": "bar"}],
["spam", {"literal": "eggs"}]
]
}
>> {foo: "bar", spam: "eggs"}# Object with explicit literal keys
{
"object": [
[{"literal": "foo"}, {"literal": "bar"}],
[{"literal": "spam"}, {"literal": "eggs"}]
]
}
>> {foo: "bar", spam: "eggs"}# Object with values of mixed types
{
"object": [
["foo", {"literal": null}],
["bar", {"literal": 1}],
["baz", {"array": [{"literal": 2}]}]
]
}
>> {foo: null, bar: 1, baz: [2]}# Nested objects
{
"object": [
[
"foo",
{
"object": [["bar", {"literal": "baz"}]]
}
]
]
}
>> {foo: {bar: "baz"}}# Object with expression keys and values
{
"defining": [
["key", {"literal": "foo"}],
["value", {"literal": 42}]
],
"result": {
"object": [
[{"name": "key"}, {"name": "value"}]
]
}
}
>> {foo: 42}# Object with spread
{
"object": [
["answer", {"literal": 42}],
{
"spread": {
"object": [
["bar", {"literal": 1}],
["baz", {"literal": 2}]
]
}
},
["question", {"literal": 69}]
]
}
>> {answer: 42, bar: 1, baz: 2, question: 69}# Object destructuring
{
"defining": [
[
{"objectPattern": ["foo", "bar"]},
{
"object": [
["bar", {"literal": 42}],
["foo", {"literal": 97}]
]
}
]
],
"result": {
"array": [
{"name": "foo"},
{"name": "foo"},
{"name": "bar"}
]
}
}
>> [97, 97, 42]# Object destructuring with rest
{
"defining": [
[
{"objectPattern": ["bar", {"rest": "others"}]},
{
"object": [
["baz", {"literal": 216}],
["bar", {"literal": 42}],
["foo", {"literal": 97}]
]
}
]
],
"result": {
"array": [
{"name": "bar"},
{"name": "others"}
]
}
}
>> [42, {baz: 216, foo: 97}]# Object destructuring with aliases
{
"defining": [
[
{
"objectPattern": [
{"name": "spam", "property": "foo"},
{"name": "eggs", "property": "bar"}
]
},
{
"object": [
["foo", {"literal": 42}],
["bar", {"literal": 97}]
]
}
]
],
"result": {
"array": [
{"name": "eggs"},
{"name": "eggs"},
{"name": "spam"}
]
}
}
>> [97, 97, 42]Defining and Calling Functions
# No parameters, no arguments
{
"defining": [
["foo", {"given": {}, "result": {"literal": 42}}]
],
"result": {"calling": {"name": "foo"}}
}
>> 42# One positional parameter, one positional argument
{
"defining": [
["foo", {"given": {"params": ["x"]}, "result": {"name": "x"}}]
],
"result": {
"calling": {"name": "foo"},
"args": [{"literal": 42}]
}
}
>> 42# One positional parameter, no arguments
{
"defining": [
["foo", {"given": {"params": ["x"]}, "result": {"name": "x"}}]
],
"result": {"calling": {"name": "foo"}}
}
!! missingArgument {"name": "x"}# One optional positional parameter, one positional argument
{
"defining": [
[
"foo",
{
"given": {
"params": [
{
"name": "x",
"defaultValue": {"literal": 73}
}
]
},
"result": {"name": "x"}
}
]
],
"result": {"calling": {"name": "foo"}, "args": [{"literal": 42}]}
}
>> 42# One optional positional parameter, no arguments
{
"defining": [
[
"foo",
{
"given": {
"params": [
{
"name": "x",
"defaultValue": {"literal": 73}
}
]
},
"result": {"name": "x"}
}
]
],
"result": {"calling": {"name": "foo"}}
}
>> 73# Default value referencing a name
{
"defining": [
["foo", {"literal": 73}],
[
"bar",
{
"given": {
"params": [
{
"name": "x",
"defaultValue": {"name": "foo"}
}
]
},
"result": {"name": "x"}
}
]
],
"result": {"calling": {"name": "bar"}}
}
>> 73# Positional rest parameter
{
"defining": [
[
"foo",
{
"given": {
"params": [{"rest": "args"}]
},
"result": {"name": "args"}
}
]
],
"result": {
"calling": {"name": "foo"},
"args": [{"literal": 42}, {"literal": 97}]
}
}
>> [42, 97]# Spread positional argument
{
"defining": [
[
"foo",
{
"given": {
"params": ["bar", "baz"]
},
"result": {
"array": [
{"name": "baz"},
{"name": "baz"},
{"name": "bar"}
]
}
}
]
],
"result": {
"calling": {"name": "foo"},
"args": [
{
"spread": {
"array": [
{"literal": 42},
{"literal": 97}
]
}
}
]
}
}
>> [97, 97, 42]# One named parameter, one argument with that name
{
"defining": [
["foo", {"given": {"namedParams": ["x"]}, "result": {"name": "x"}}]
],
"result": {
"calling": {"name": "foo"},
"namedArgs": [["x", {"literal": 42}]]
}
}
>> 42# One named parameter, no arguments
{
"defining": [
["foo", {"given": {"namedParams": ["x"]}, "result": {"name": "x"}}]
],
"result": {"calling": {"name": "foo"}}
}
!! missingArgument {"name": "x"}# One named parameter, one positional argument
{
"defining": [
["foo", {"given": {"namedParams": ["x"]}, "result": {"name": "x"}}]
],
"result": {
"calling": {"name": "foo"},
"args": [{"literal": 42}]
}
}
!! missingArgument {"name": "x"}# Named rest parameter
{
"defining": [
[
"foo",
{
"given": {
"namedParams": [{"rest": "namedArgs"}]
},
"result": {"name": "namedArgs"}
}
]
],
"result": {
"calling": {"name": "foo"},
"namedArgs": [
["bar", {"literal": 42}],
["baz", {"literal": 97}]
]
}
}
>> {bar: 42, baz: 97}# Spread named argument
{
"defining": [
[
"foo",
{
"given": {
"namedParams": ["bar", "baz"]
},
"result": {
"array": [
{"name": "baz"},
{"name": "baz"},
{"name": "bar"}
]
}
}
]
],
"result": {
"calling": {"name": "foo"},
"namedArgs": [
{
"spread": {
"object": [
["bar", {"literal": 42}],
["baz", {"literal": 97}]
]
}
}
]
}
}
>> [97, 97, 42]# Array destructuring in parameters
{
"defining": [
[
"foo",
{
"given": {
"params": [
{"arrayPattern": ["foo", "bar"]}
]
},
"result": {
"array": [
{"name": "bar"},
{"name": "bar"},
{"name": "foo"}
]
}
}
]
],
"result": {
"calling": {"name": "foo"},
"args": [
{
"array": [
{"literal": 42},
{"literal": 97}
]
}
]
}
}
>> [97, 97, 42]# Calling a non-function
{
"calling": {"literal": 42}
}
!! notCallable {"value": 42}# A name from an enclosing function
{
"defining": [
["x", {"literal": 73}],
[
"foo",
{
"given": {"params": ["y"]},
"result": {
"array": [
{"name": "x"},
{"name": "y"}
]
}
}
]
],
"result": {"calling": {"name": "foo"}, "args": [{"literal": 42}]}
}
>> [73, 42]A function body can reference names that were in scope when the function was defined, even if those names are out of scope when the function is called.
# Closure
{
"calling": {
"calling": {
"given": {},
"result": {
"defining": [["x", {"literal": 73}]],
"result": {
"given": {"params": ["y"]},
"result": {
"array": [
{"name": "x"},
{"name": "y"}
]
}
}
}
}
},
"args": [{"literal": 42}]
}
>> [73, 42]On the other hand, names that are in scope when the function is called don’t leak into the function body.
# Leakage
{
"defining": [
[
"leaky",
{"given": {"params": ["x"]}, "result": {"name": "intruder"}}
]
],
"result": {
"defining": [
["intruder", {"literal": 42}]
],
"result": {"calling": {"name": "leaky"}, "args": [{"literal": 73}]}
}
}
!! nameNotDefined {"name": "intruder"}Indexing
# Indexing strings
{
"indexing": {"literal": "foobar"},
"at": {"literal": 4}
}
>> "b"# Indexing strings - wrong index type
{
"indexing": {"literal": "foobar"},
"at": {"literal": "baz"}
}
!! wrongType {"value": "baz", "expectedType": "number"}# Indexing arrays
{
"indexing": {
"array": [
{"literal": "foo"},
{"literal": "bar"}
]
},
"at": {"literal": 2}
}
>> "bar"# Indexing arrays - index from end
{
"indexing": {
"array": [
{"literal": "foo"},
{"literal": "bar"}
]
},
"at": {"literal": -2}
}
>> "foo"# Indexing arrays - wrong index type
{
"indexing": {
"array": [
{"literal": "foo"},
{"literal": "bar"}
]
},
"at": {"literal": "baz"}
}
!! wrongType {"value": "baz", "expectedType": "number"}# Indexing arrays - index less than minus length
{
"indexing": {
"array": [
{"literal": "foo"},
{"literal": "bar"}
]
},
"at": {"literal": -3}
}
!! indexOutOfBounds {"value": ["foo", "bar"], "length": 2, "index": -3}# Indexing arrays - index 0
{
"indexing": {
"array": [
{"literal": "foo"},
{"literal": "bar"}
]
},
"at": {"literal": 0}
}
!! indexOutOfBounds {"value": ["foo", "bar"], "length": 2, "index": 0}# Indexing arrays - index greater than length
{
"indexing": {
"array": [
{"literal": "foo"},
{"literal": "bar"}
]
},
"at": {"literal": 3}
}
!! indexOutOfBounds {"value": ["foo", "bar"], "length": 2, "index": 3}# Indexing objects
{
"indexing": {
"object": [
["foo", {"literal": "bar"}],
["spam", {"literal": "eggs"}]
]
},
"at": {"literal": "spam"}
}
>> "eggs"# Indexing objects - wrong index type
{
"indexing": {
"object": [
["foo", {"literal": "bar"}],
["spam", {"literal": "eggs"}]
]
},
"at": {"literal": 42}
}
!! wrongType {"value": 42, "expectedType": "string"}{
"indexing": {
"object": [
["foo", {"literal": "bar"}],
["spam", {"literal": "eggs"}]
]
},
"at": {"literal": "baz"}
}
!! missingProperty {"value": {foo: "bar", spam: "eggs"}, "key": "baz"}# Indexing something non-indexable
{
"indexing": {"literal": 42},
"at": {"literal": 2}
}
!! wrongType {"value": 42, "expectedType": {"either": ["string", "array", "object"]}}Errors
# Error short-circuiting through function calls
{
"calling": {
"given": {},
"result": {"literal": 42}
},
"args": [
{
"defining": [
[{"arrayPattern": ["foo"]}, {"array": []}]
],
"result": {"name": "foo"}
}
]
}
!! missingElement {"name": "foo"}# Error short-circuiting through arrays
{
"array": [
{
"defining": [
[{"arrayPattern": ["foo"]}, {"array": []}]
],
"result": {"name": "foo"}
}
]
}
!! missingElement {"name": "foo"}# Error short-circuiting through objects
{
"object": [
[
"foo",
{
"defining": [
[{"arrayPattern": ["foo"]}, {"array": []}]
],
"result": {"name": "foo"}
}
]
]
}
!! missingElement {"name": "foo"}# Error catching
{
"calling": {
"given": {},
"result": {"literal": 42}
},
"args": [
{
"catching": {
"defining": [
[{"arrayPattern": ["foo"]}, {"array": []}]
],
"result": {"name": "foo"}
}
}
]
}
>> 42