Add Bimonad for Function0

katz/src/main/kotlin/katz/instances/Function0Bimonad.kt

@@ -0,0 +1,34 @@
+package katz
+
+// We don't we want an inherited class to avoid equivalence issues, so a simple HK wrapper will do
+data class Function0<out A>(internal val f: () -> A) : HK<Function0.F, A> {
+
+    class F private constructor()
+
+    companion object : Bimonad<Function0.F>, GlobalInstance<Bimonad<Function0.F>>() {
+
+        override fun <A, B> flatMap(fa: HK<Function0.F, A>, f: (A) -> HK<Function0.F, B>): HK<Function0.F, B> =
+                f(fa.ev().invoke())
+
+        override fun <A, B> coflatMap(fa: HK<Function0.F, A>, f: (HK<Function0.F, A>) -> B): HK<Function0.F, B> =
+                { f(fa) }.k()
+
+        override fun <A> pure(a: A): HK<Function0.F, A> =
+                { a }.k()
+
+        override fun <A> extract(fa: HK<Function0.F, A>): A =
+                fa.ev().invoke()
+
+        override fun <A, B> tailRecM(a: A, f: (A) -> HK<F, Either<A, B>>): HK<F, B> =
+                f(a).ev().invoke().let { either ->
+                    when (either) {
+                        is Either.Left -> tailRecM(either.a, f)
+                        is Either.Right -> ({ either.b }).k()
+                    }
+                }
+    }
+}
+
+fun <A> (() -> A).k(): HK<Function0.F, A> = Function0(this)
+
+fun <A> HK<Function0.F, A>.ev() = (this as Function0<A>).f

katz/src/test/kotlin/katz/data/CoreaderTest.kt

@@ -1,9 +1,8 @@
-package katz.data
+package katz
 
 import io.kotlintest.KTestJUnitRunner
 import io.kotlintest.matchers.shouldBe
 import io.kotlintest.properties.forAll
-import katz.*
 import org.junit.runner.RunWith
 
 @RunWith(KTestJUnitRunner::class)

katz/src/test/kotlin/katz/data/Function0Test.kt

@@ -0,0 +1,33 @@
+package katz
+
+import io.kotlintest.KTestJUnitRunner
+import io.kotlintest.matchers.shouldBe
+import org.junit.runner.RunWith
+
+@RunWith(KTestJUnitRunner::class)
+class Function0Test : UnitSpec() {
+    init {
+        "Function0Monad.binding should for comprehend over all values of multiple Function0" {
+            Function0.binding {
+                val x = Function0 { 1 }.bind()
+                val y = !Function0 { 2 }
+                val z = bind { Function0 { 3 } }
+                yields(x + y + z)
+            }.ev().invoke() shouldBe 6
+        }
+
+        "Function0Comonad.cobinding should for comprehend over all values of multiple Function0" {
+            Function0.cobinding {
+                val x = Function0 { 1 }.extract()
+                val y = !Function0 { 2 }
+                val z = extract { Function0 { 3 } }
+                yields(x + y + z)
+            } shouldBe 6
+        }
+
+        "Function0Comonad.duplicate should create an instance of Function0<Function0<A>>" {
+            Function0.duplicate(Function0 { 3 }).ev().invoke().ev().invoke() shouldBe
+                    Function0 { Function0 { 3 } }.ev().invoke().ev().invoke()
+        }
+    }
+}

katz/src/test/kotlin/katz/data/IdTest.kt

@@ -1,11 +1,7 @@
-package katz.data
+package katz
 
 import io.kotlintest.KTestJUnitRunner
 import io.kotlintest.matchers.shouldBe
-import katz.Id
-import katz.UnitSpec
-import katz.binding
-import katz.cobinding
 import org.junit.runner.RunWith
 
 @RunWith(KTestJUnitRunner::class)

katz/src/test/kotlin/katz/data/ReaderTest.kt

@@ -1,8 +1,7 @@
-package katz.data
+package katz
 
 import io.kotlintest.KTestJUnitRunner
 import io.kotlintest.matchers.shouldBe
-import katz.*
 import org.junit.runner.RunWith
 
 @RunWith(KTestJUnitRunner::class)