Algebra and Interpreters for Describing CRUD Applications.
Branch: master
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
Failed to load latest commit information.


** Please note that the Bones project is currently a work in progress. **


The purpose of this library is to remove as much boilerplate as possible out of a CRUD/REST application.
Some REST services (including Swagger doc) can be written in as little as 5 expressions.

  • Define the input and output and error schema -- Using a declarative syntax, describe the expected data.
  • Define the allowable CRUD actions for a schema type.
  • Pass the items to an interpreter.

Schema DSL

Bones defines a Domain Specific Language (DSL) for describing CRUD applications with validation.

Using the DSL will result in creating a Generalized Algebraic Data Type (GADT) data structure. The GADT structure describes the data, validation and available Create/Read/Update/Delete (CRUD) actions.

As an example, we will describe a Person CRUD application. For a complete running service writing to the Database, refer to the Example

import com.bones.syntax._
import com.bones.validation.ValidationDefinition.{IntValidation => iv, StringValidation => sv}

case class Person(name: String, age: Int)

val personSchema = (
  kvp("name", string(sv.matchesRegex("^[a-zA-Z ]*$".r))) ::
  kvp("age", int(iv.min(0))) ::

case class Error(error: String)
val errorDef = (kvp("error", string) :: KvpNil).convert[Error]

val personService = ServiceOps.withPath("person")
    .withCreate(personSchema, personWithId, errorDef)
    .withRead(personWithId, errorDef)
    .withUpdate(personSchema, personWithId, errorDef)
    .withDelete(personWithId, errorDef)


The power in creating a GADT structure, is that we can provide different interpretations of the defined Schema. Once the basic description of the service is created, many different programs can interpret not only the data structure in different contexts, but also define implied behavior. If implied behavior is similar between systems, then the exact same interpreter can be used across services and the only change would be the schema and service description as described above.

I other words, if services perform similar behavior, such as write to Kafka, S3, a Database or an external services, the boilerplate code can be reduced by using GADTs. This project is to provide a common vocabulary, and reasonable API, for any CRUD service. See below for the list of interpreters.

This example uses the Scala http4s.

val service =
    // .withContentType(protobufFormat) Not implemented yet.

// The generated endpoint will take care of unmarshalling JSON and validating against the schema defined above.
// If successfull, will pass the Person case class to the specified function.
// Also responsible for marshalling the Error or Successful Results.
val http4Service: HttpRoutes[IO] = service.forService(
    person => IO { Right(person) }, // create: a function from Person => IO[Either[Error,Person]] 
    id => IO { Right(Person("Janis Ian", 30, None))}, //read: a function from long => IO[Either[Error,Person]]
    (id, person) => IO { Right(person) }, //update: a function from (long,Person) => IO[Either[Error, Person]]
    id => IO { Right(Person("Janis Ian", 30, None))} // delete: a function from (long) => IO[Either[Error, Person]]

object PersonEndpoint extends IOApp {

  override def run(args: List[String]): IO[ExitCode] = {

    BlazeBuilder[IO].bindHttp(8080, "localhost").mountService(http4Service, "/")

We can use the same schema to generate Swagger compliant doc. This will eventually be integrated in the http4s interpreter.

val openApi = new OpenAPI()




Version 0.5.0-SNAPSHOT includes validation, CRUD and the http4s REST Interpreter.

Http4s Circe Interpreter (currently the only interpreter)

Basic CRUD capabilities implemented with http4s, circe and doobie. libraryDependencies += "com.github.oletraveler" %% "bones-http4s-circe" % "0.5.0-SNAPSHOT"


Build Status


  • "Your bones got a little machine" - Black Francis
  • The API for this project is adapted from the Joi Project .
  • John De Goes Free Applicative Talk
  • Kris Knuttycombe's Xenomorph Library is similar to this.
  • Scodec is an amazing library. I learned a lot from that library.