Intro

An implementation of JSON Schema Draft 4 in haskell.

Status

Still in development. Lacks solid code to fetch remote schemas.

Example

{-# LANGUAGE OverloadedStrings #-}

module Main where

import Data.Aeson
import qualified Data.HashMap.Strict as H
import qualified Data.JsonSchema as JS
import qualified Data.Vector as V

main :: IO ()
main = do
  eitherGraph <- JS.fetchRefs JS.draft4 rawSchema H.empty
  case eitherGraph of
    Left e  -> print e
    Right g ->
      case JS.compileDraft4 g rawSchema of
        Left e2 -> print e2
        Right a -> print $ JS.validate a invalidData

rawSchema :: JS.RawSchema
rawSchema = JS.RawSchema
  { JS._rsURI = ""
  , JS._rsObject = H.singleton "uniqueItems" (Bool True) -- Schema JSON goes here.
  }

invalidData :: Value
invalidData = Array (V.fromList ["foo", "foo"])

Output:

fromList ["Val error against uniqueItems True for: Array (fromList [String \"foo\",String \"foo\"])"]

Install Tests

git submodule update --init

Run Tests

cd JSON-Schema-Test-Suite/remotes
python -m SimpleHTTPServer 1234

Then run the normal cabal test from another terminal.

Note that the tests require an internet connection.

Notes

• This uses the regexpr regular expression library fo the "pattern" validator. I have no idea if this is compatible with the ECMA 262 regex dialect, which the spec requires.

• draft4.json is from commit # cc8ec81ce0abe2385ebd6c2a6f2d6deb646f874a here.

Credits

Thanks to Julian Berman for the fantastic test suite.

Also thanks to Tim Baumann for his aeson-schema library. Hjsonschema's test code and its implementation of Graph both come from Aeson-Schema.