circe / circe-droste

Recursion schemes for Circe

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This project includes some tools for working with Circe's representation of JSON documents using recursion schemes. It currently includes a pattern functor for io.circe.Json and some basic integration with Droste.


Count all the nulls anywhere in a document!

import higherkindness.droste.Algebra, higherkindness.droste.scheme.cata
import io.circe.pattern.JsonF, io.circe.droste._, io.circe.literal._

val nullCounter: Algebra[JsonF, Int] = Algebra {
  case JsonF.NullF => 1
  case JsonF.ArrayF(xs) => xs.sum
  case JsonF.ObjectF(fs) =>
  case _ => 0

val doc = json"""{"x":[null,{"y":[1,null,true,[null,null]]}]}"""

val result = cata(nullCounter).apply(doc) // result: Int = 4

Or you can use Droste's foldMap:

import higherkindness.droste.syntax.project._
import io.circe.droste._, io.circe.literal._

val doc = json"""{"x":[null,{"y":[1,null,true,[null,null]]}]}"""

val result = doc.foldMap(j => if (j.isNull) 1 else 0) // result: Int = 4

Contributors and participation

This project supports the Scala code of conduct and we want all of its channels (Gitter, GitHub, etc.) to be welcoming environments for everyone.

Please see the Circe contributors' guide for details on how to submit a pull request.


circe-droste is licensed under the Apache License, Version 2.0 (the "License"); you may not use this software except in compliance with the License.

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.