A Haskell implementation of the most commonly used [JSON Schema](http://json-schema.org/) specification ([Draft 4](https://github.com/json-schema-org/json-schema-spec/wiki/Specification-Links#draft-4)).
[Hackage](https://hackage.haskell.org/package/hjsonschema) / [GitHub](https://github.com/seagreen/hjsonschema) / [Travis CI](https://travis-ci.org/seagreen/hjsonschema)
# Notes
+ As of 2017 [json-schema-org](https://github.com/json-schema-org/json-schema-spec) has begun releasing new drafts of the standard. Once this work stabilizes `hjsonschema` will add coverage for the latest draft.
+ Requires [pcre](http://www.pcre.org/) (`pkgs.pcre` in Nixpkgs).
+ Schemas with circular references can cause infinite loops. hjsonschema does loop detection but it may not be solid yet -- please open an issue if you find a situation where it fails.
# Example
See [here](https://github.com/seagreen/hjsonschema/blob/master/examples/Simple.hs).
# Tests
Run all tests:
`stack test`
Run only local tests:
`stack test hjsonschema:local`
Run remote tests (makes GETs to json-schema.org, also temporarily starts an HTTP server on port 1234):
`stack test hjsonschema:remote`
# Details
## Goals
+ Be a correct and fast implementation of the spec.
+ Be a useful reference for implementers in other languages. Haskell's high level nature, expressive type system and referential transparency suit this purpose well.
## Good Parts
+ Passes all the required tests in the [language agnostic test suite](https://github.com/json-schema/JSON-Schema-Test-Suite).
+ Very modular, which should make it easy to support future versions of the specification.
## Bad Parts
+ Uses the [pcre-heavy](https://hackage.haskell.org/package/pcre-heavy) regular expression library for the "pattern" validator. It should use a library based on the ECMA 262 regex dialect, which the [spec](http://json-schema.org/latest/json-schema-validation.html#anchor33) requires.
+ Currently doesn't support the optional `"format"` validators.
## Vendoring
+ `JSON-Schema-Test-Suite` is vendored from commit # aabcb3427745ade7a0b4d49ff016ad7eda8b898b [here](https://github.com/json-schema-org/JSON-Schema-Test-Suite).
+ `src/draft4.json` is from commit # f3d5aeb5ffbe9d9a5a0ceb761dc47c7c4c2efa68 [here](https://github.com/json-schema/json-schema).
## Credits
[TJ Weigel](http://tjweigel.com/) created the logo.
[Tim Baumann](https://github.com/timjb) wrote [aeson-schema](https://hackage.haskell.org/package/aeson-schema), on which hjsonschema's test code and its implementation of `SchemaGraph` were based.
[Julian Berman](https://github.com/Julian) maintains the fantastic [language agnostic test suite](https://github.com/json-schema/JSON-Schema-Test-Suite).