json-pointer

JSON Pointers (RFC 6901) for Aeson.

This library implements:

• A JsonPointer type, which can be constructed from fragments via a Monoid instance
• A parser and a printer, including support for the ~1 and ~0 escape sequences
• FromJSON, ToJSON and ToSchema (openapi3) instances
• Functions for pointing into Aeson Values

Parser accepts both the plain form ("/foo/bar") and the relative URI form ("#/foo/bar"), but no URL decoding is performed in either case.

Printer always produces the plain form.

Example

You can use make repl to start a REPL with the library loaded.

>>> import Data.Aeson
>>> import Data.JsonPointer

>>> let doc = object ["foo" .= [object ["bar" .= (1 :: Int)]]]
>>> let pointer = atKey "foo" <> atIndex 0 <> atKey "bar"

>>> pointTo pointer doc
Just (Number 1.0)

>>> show pointer
"/foo/0/bar"

>>> parseJsonPointer "#/foo/0/bar"
Right /foo/0/bar

Checks

make check         # format-check, lint and test
make format        # apply the formatting instead of just checking it

The individual checks are make format-check (fourmolu over src and test, cabal-fmt over the cabal file), make lint (hlint) and make test. make help lists the rest.

The tools are not part of the build, install them once:

cabal install fourmolu cabal-fmt hlint

The same three checks run on every pull request, see .github/workflows/ci.yaml.

Provenance

This library is based off of https://hackage.haskell.org/package/json-pointer.

The license to the original code is included in the LICENSE file.