Added Defer instance, bump to 0.2.0. (#1)

By adding `Defer[Parsley]`, there is now support for idiomatic recursive
parser construction.

README.md

@@ -2,24 +2,26 @@
 
 
 ## What is `parsley-cats`?
-The `parsley-cats` library exposes `cats` instances for `MonoidK[Parsley]`, `Monad[Parsley]`, and `FunctorFilter[Parsley]`.
+The `parsley-cats` library exposes `cats` instances for `MonoidK[Parsley]`, `Monad[Parsley]`, and `FunctorFilter[Parsley]` as well as `Defer[Parsley]`.
 Care should still be taken to not define truly recursive parsers using the `cats` API (although monadic parser with `flatMap`
-may be generally recursive, just slow).
+may be generally recursive, just slow). In particular, make use of `Defer[Parsley].fix`
+to handle recursion, or plain `lazy val` based construction (as in regular `parsley` use).
 
 ## How do I use it? [![parsley-cats Scala version support](https://index.scala-lang.org/j-mie6/parsley-cats/parsley-cats/latest-by-scala-version.svg?platform=jvm)](https://index.scala-lang.org/j-mie6/parsley-cats/parsley-cats) [![parsley-cats Scala version support](https://index.scala-lang.org/j-mie6/parsley-cats/parsley-cats/latest-by-scala-version.svg?platform=sjs1)](https://index.scala-lang.org/j-mie6/parsley-cats/parsley-cats) [![parsley-cats Scala version support](https://index.scala-lang.org/j-mie6/parsley-cats/parsley-cats/latest-by-scala-version.svg?platform=native0.4)](https://index.scala-lang.org/j-mie6/parsley-cats/parsley-cats)
 
 Parsley cats is distributed on Maven Central, and can be added to your project via:
 
 ```scala
-libraryDependencies += "com.github.j-mie6" %% "parsley-cats" % "0.1.0"
+libraryDependencies += "com.github.j-mie6" %% "parsley-cats" % "0.2.0"
 ```
 
 it requires `parsley` and `cats-core` to also be dependencies of your project. The current version
 matrix for `parsley-cats`:
 
 | `parsley-cats` version | `parsley` version | `cats-core` version |
 | :--------------------: | :---------------: | :-----------------: |
-| `0.1.0`                | `>= 4 && < 5`     | `>= 2.8 && < 3`     |
+| `0.1.x`                | `>= 4 && < 5`     | `>= 2.8 && < 3`     |
+| `0.2.x`                | `>= 4 && < 5`     | `>= 2.8 && < 3`     |
 
 Documentation can be found [**here**][Link-Scaladoc]
 

build.sbt

@@ -8,7 +8,7 @@ val Scala3 = "3.2.1"
 Global / onChangedBuildSource := ReloadOnSourceChanges
 
 inThisBuild(List(
-  tlBaseVersion := "0.1",
+  tlBaseVersion := "0.2",
   organization := "com.github.j-mie6",
   startYear := Some(2022),
   homepage := Some(url("https://github.com/j-mie6/parsley-cats")),
@@ -38,7 +38,10 @@ lazy val `parsley-cats` = crossProject(JVMPlatform, JSPlatform, NativePlatform)
       "com.github.j-mie6" %%% "parsley" % "4.0.0" % Provided,
       "org.scalatest" %%% "scalatest" % "3.2.12" % Test,
       "org.typelevel" %%% "cats-laws" % "2.8.0" % Test,
-    )
+    ),
+    mimaPreviousArtifacts := Set(
+      "com.github.j-mie6" %% "parsley-cats" % "0.1.0",
+    ),
   )
   .jsSettings(
       Test / scalaJSLinkerConfig := scalaJSLinkerConfig.value.withESFeatures(_.withESVersion(ESVersion.ES2018))

parsley-cats/shared/src/main/scala/parsley/DeferForParsley.scala

@@ -0,0 +1,9 @@
+package parsley
+
+import cats.Defer
+
+import Parsley.LazyParsley
+
+private [parsley] class DeferForParsley extends Defer[Parsley] {
+    def defer[A](p: =>parsley.Parsley[A]): parsley.Parsley[A] = ~p
+}

parsley-cats/shared/src/main/scala/parsley/cats.scala

@@ -3,7 +3,7 @@
  */
 package parsley
 
-import cats.{Monad, MonoidK, FunctorFilter}
+import cats.{Monad, MonoidK, FunctorFilter, Defer}
 
 /** Contains instances for `cats` typeclasses.
   *
@@ -20,4 +20,10 @@ object catsinstances {
                             with FunctorForParsley
                             with MonoidKForParsley
                             with FunctorFilterForParsley
+
+    /** Instance for `cats` `Defer` typeclass, which allows for recursive parser generation.
+      *
+      * @since 0.2.0
+      */
+    implicit val deferForParsley: Defer[Parsley] = new DeferForParsley
 }

parsley-cats/shared/src/test/scala/parsley/CatsSuite.scala

@@ -4,6 +4,7 @@ import org.scalatest.flatspec.AnyFlatSpec
 import org.scalatest.matchers.should.Matchers._
 import org.scalactic.source.Position
 
+import parsley.Parsley.pure
 import parsley.character.{item, digit, char}
 import parsley.catsinstances._
 
@@ -48,4 +49,11 @@ class CatsSuite extends AnyFlatSpec {
         applyLaw(monoidKLaws.monoidKLeftIdentity(item), monoidKLaws.monoidKRightIdentity(item))("", "a", "b")
         applyLaw(monoidKLaws.combineAllK(Vector(char('a'), char('b'), char('c'))))("", "a", "b", "c")
     }
+
+    "Defer" should "allow for the construction of recursive parsers" in {
+        val manya = deferForParsley.fix[List[Char]] { self =>
+            char('a') <::> self <|> pure(Nil)
+        }
+        manya.parse("aaaaaaaaaaaab") shouldBe Success(List.fill(12)('a'))
+    }
 }