# `json_pointer`

The `json_pointer` library provides predicates for parsing, generating, and evaluating JSON Pointers as specified by RFC 6901, plus support for Relative JSON Pointer:

- https://www.rfc-editor.org/rfc/rfc6901

- https://json-schema.org/draft/2020-12/relative-json-pointer

It supports both the plain string syntax and the URI fragment syntax for absolute JSON Pointers. Relative JSON Pointers use the plain string syntax. Reference tokens can be represented as atoms, `chars(List)`, or `codes(List)`.

## API documentation

Open the ../../apis/library_index.html#json_pointer link in a web browser.

## Loading

To load all entities in this library, load the `loader.lgt` file:

    | ?- logtalk_load(json_pointer(loader)).

## Testing

To test this library predicates, load the `tester.lgt` file:

    | ?- logtalk_load(json_pointer(tester)).

## Representation

The library defines the `json_pointer(_Representation_)` parametric object where `_Representation_` can be one of:

- `atom` - reference tokens are represented as atoms

- `chars` - reference tokens are represented as `chars(List)`

- `codes` - reference tokens are represented as `codes(List)`

When using the default `json_pointer` object, reference tokens are represented as atoms.

Relative JSON Pointer values are represented as `relative(Up, Shift, Suffix)`:

- `Up` is the number of ancestor steps

- `Shift` is the optional signed array index adjustment

- `Suffix` is either a list of reference tokens or the atom `'#'`

## Examples

Parse and evaluate a pointer:

    | ?- json_pointer::parse(atom('/foo/0'), Pointer),
         json_pointer::evaluate(Pointer, {foo-[bar, baz]}, Value).
    Pointer = [foo, '0']
    Value = bar
    yes

Generate a URI fragment representation:

    | ?- json_pointer::generate_fragment(atom(Fragment), ['a b', 'c/d']).
    Fragment = '#/a%20b/c~1d'
    yes

Evaluate a Relative JSON Pointer from a known context path:

    | ?- json_pointer::evaluate_relative(relative(1, 0, ['0']), [foo, '1'], {foo-[bar, baz]}, Value).
    Value = bar
    yes