dhallj-magnolia

This library provides generic derivation of dhallj Encoder and Decoder typeclasses using magnolia.

To use dhallj-magnolia add the following dependency to your build.sbt:

libraryDependencies += "pl.msitko" %% "dhallj-magnolia" % "0.1.3"

Limitations of Scala 3 version of the library

Dhallj-magnolia is published for both Scala 2.13 and Scala 3. Limitations of Scala 3 branch of the library:

• Your project consuming dhallj-magnolia has to have the compilation flag -Yretain-trees enabled if you rely on default values for case classes
• Derivation doesn't work for value classes

Examples

Consider the following ADT:

sealed trait Bar
final case class Bar1(a: Int) extends Bar
final case class Bar2(b: String) extends Bar
final case class Foo(a: Int, b: String, bar: Bar)

Automatic Encoder derivation

import org.dhallj.codec.syntax._
import pl.msitko.dhallj.generic.encoder.auto._

val input = Foo(12, "abc", Bar2("abcd"))
input.asExpr.toString
// """{a = 12, b = "abc", bar = (<Bar1 : {a : Natural} | Bar2 : {b : Text}>.Bar2) {b = "abcd"}}"""

Additionally, dhallj's Encoder[A] has dhallType method which prints out dhall type for A. So, following the example, we can:

import org.dhallj.codec.Encoder
println(Encoder[Foo].dhallType(None, None))
// {a : Natural, b : Text, bar : <Bar1 : {a : Natural} | Bar2 : {b : Text}>}

Automatic Decoder derivation

import org.dhallj.syntax._
import pl.msitko.dhallj.generic.decoder.auto._

val input = """{a = 12, b = "abc", bar = (<Bar1 : {a : Natural} | Bar2 : {b : Text}>.Bar2) {b = "abcd"}}"""

for {
  parsed  <- input.parseExpr
  decoded <- parsed.normalize().as[Foo]
} yield decoded
// Right(Foo(12,abc,Bar2(abcd)))

Semi-automatic Encoder derivation

import org.dhallj.codec.syntax._
import pl.msitko.dhallj.generic.encoder.semiauto._

implicit val barEncoder = deriveEncoder[Bar]
implicit val fooEncoder = deriveEncoder[Foo]

val input = Foo(12, "abc", Bar2("abcd"))
input.asExpr.toString
// """{a = 12, b = "abc", bar = (<Bar1 : {a : Natural} | Bar2 : {b : Text}>.Bar2) {b = "abcd"}}"""

Semi-automatic Decoder derivation

import org.dhallj.syntax._
import pl.msitko.dhallj.generic.decoder.semiauto._

implicit val barDecoder = deriveDecoder[Bar]
implicit val fooDecoder = deriveDecoder[Foo]

val input = """{a = 12, b = "abc", bar = (<Bar1 : {a : Natural} | Bar2 : {b : Text}>.Bar2) {b = "abcd"}}"""

for {
  parsed  <- input.parseExpr
  decoded <- parsed.normalize().as[Foo]
} yield decoded
// Right(Foo(12,abc,Bar2(abcd)))