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https://github.com/paurkedal/ocaml-kojson
Combinators for matching JSON
https://github.com/paurkedal/ocaml-kojson
json ocaml parser-combinators yojson
Last synced: 2 days ago
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Combinators for matching JSON
- Host: GitHub
- URL: https://github.com/paurkedal/ocaml-kojson
- Owner: paurkedal
- License: lgpl-3.0
- Created: 2013-11-16T09:45:17.000Z (about 11 years ago)
- Default Branch: master
- Last Pushed: 2023-01-07T09:23:48.000Z (about 2 years ago)
- Last Synced: 2025-01-10T22:47:35.273Z (12 days ago)
- Topics: json, ocaml, parser-combinators, yojson
- Language: OCaml
- Homepage: http://paurkedal.github.io/ocaml-kojson/
- Size: 51.8 KB
- Stars: 3
- Watchers: 4
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- Changelog: CHANGES.md
- License: COPYING
Awesome Lists containing this project
README
# Kojson - JSON Parser Combinators
## Synopsis
Kojson provides combinators to construct functions to match JSON values in a
convenient and asymptotically efficient way. The patterns take as input the
polymorphic variant `Yojson.Basic.json` wrapped with location information
for precise error reporting. The library provides two top-level modules:
* `Kojson` - Contains general definitions.
* `Kojson_pattern` - Contains the combinators. You should open this where
needed. It provides a `K` substructure to match trees, a `Ka`
substructure to match associations, and some operators.
For details, see [the API reference](http://paurkedal.github.io/ocaml-kojson/).
### Example
The following decodes a list of objects containing two mandatory and one
optional attributes:
```OCaml
open Kojson_pattern
open Unprime
open Unprime_option
let decode_log =
K.list begin
K.assoc begin
"time"^: K.int %> fun time ->
"facility"^?: Option.map K.string %> fun facility_opt ->
"message"^: K.string %> fun message ->
Ka.stop (time, facility_opt, message)
end
end
```
The input to this is constructed with `Kojson.jin_of_json` and it will throw
a `Kojson.Mismatch` exception if the pattern does not match. E.g. loading
the JSON data from a file:
```OCaml
let handle_error fp msg = failwith ("Cannot load "^fp^": "^msg^"\n")
let load_log_file fp =
try decode_log (Kojson.jin_of_json (Yojson.Basic.from_file fp)) with
| Yojson.Json_error msg -> handle_error fp msg
| Kojson.Mismatch (path, expect) ->
handle_error fp (Kojson.string_of_mismatch (path, expect))
```
If the file does not contain valid JSON data, then Yojson will point to the
file and line number. If the pattern does not match, then Kojson will
indicate the logical path of the mismatch using labels and indices.
## Installation
The package is available though the [author's OPAM repository][1]:
opam repo add paurkedal https://github.com/paurkedal/opam-repo-paurkedal.git
opam install kojson
Alternatively use `topkg/pkg.ml` (or `opam pin`) from a Git checkout or tar
extraction.
### Dependencies
* [Prime](https://github.com/paurkedal/ocaml-prime)
* [Topkg](http://erratique.ch/software/topkg) (build only)
* [Yojson](http://mjambon.com/yojson.html)
### See Also
* [atdgen](https://github.com/mjambon/atdgen)
* [deriving-yojson](https://github.com/hhugo/deriving-yojson)
* [jsont](http://erratique.ch/software/jsont)
* [piqi](http://piqi.org/)
* [ppx_deriving_yojson](https://github.com/whitequark/ppx_deriving_yojson)
[1]: https://github.com/paurkedal/opam-repo-paurkedal