package jsont

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Indices
Paths
Path syntax

package jsont

jsont
- Jsont
  - Array
  - Base
  - Error
    
    Context
  - Json
  - Meta
  - Object
    
    Case
    
    Mem
    
    Mems
  - Path
  - Repr
    
    Dict
    
    Type
    
    Id
  - Sort
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JSON paths.

Paths are used for keeping track of erroring contexts and for specifying query and update locations.

Indices

type index =

| Mem of string node
(*
Indexes the value of the member n of an object.
*)
| Nth of int node
(*
Indexes the value of the nth element of an array.
*)

The type for indexing operations on JSON values.

val pp_index : index fmt

pp_index formats indexes.

val pp_index_trace : index fmt

pp_index formats indexes and their location.

Paths

type t

The type for paths, a sequence of indexing operations.

val root : t

root is the root path.

val is_root : t -> bool

is_root p is true iff p is the root path.

val nth : ?meta:Meta.t -> int -> t -> t

nth n p indexes the array indexed by p at index n.

val mem : ?meta:Meta.t -> string -> t -> t

mem n p indexes the object indexed by p at member n.

val rev_indices : t -> index list

rev_indices p are the indices of p in reverse order, the last indexing operation appears first.

val of_string : string -> (t, string) Stdlib.result

of_string s parses a path according to the path syntax.

val pp : t fmt

pp formats paths.

val pp_trace : t fmt

pp_trace formats paths as a stack trace, if not empty.

Path syntax

Path provide a way for end users to address JSON and edit locations.

A path is a sequence of member and list indexing operations. Applying the path to a JSON value leads to either a JSON value, or nothing if one of the indices does not exist, or an error if ones tries to index a non-indexable value.

Here are a few examples of paths.

{
  "ocaml": {
    "libs": ["jsont", "brr", "cmdliner"]
  }
}

ocaml.libs        # value of member "libs" of member "ocaml"
ocaml.libs.[0]    # first element of member "libs" of member "ocaml"

More formally a path is a . seperated list of indices. An index is written [i]. i can a zero-based list index. Or i can be an object member name n. If there is no ambiguity, the surrounding brackets can be dropped.

Notes.

The syntax has no form of quoting at the moment this means key names can't contain, [, ], or start with a number.
It would be nice to be able to drop the dots in order to be compatible with JSONPath syntax.
Reintroduce and implement negative indices (they are parsed).