diff --git a/README.md b/README.md
index 7591b688e696c12b93f5a2740a3e7726631774c3..89261a2a4fdb1a5c3e60b9a40f67a059a67637b3 100644
--- a/README.md
+++ b/README.md
@@ -18,6 +18,9 @@ usually marked with `???`. Lectures not listed here are not migrated to Scala
| 4: Laziness | [`laziness`](src/main/scala/laziness/) | `testOnly laziness.*`
| 5: Algebras, Laws and monoids | [`algebra`](src/main/scala/algebra/) | `testOnly algebra.*`
| 6: Foldables and Functors | [`foldfunc`](src/main/scala/foldfunc/) | `testOnly foldfunc.*`
+| 7: Monads | [`monads`](src/main/scala/monads/) | `testOnly monads.*`
+| 8: Applicative Functors | [`applicative`](src/main/scala/applicative/) | `testOnly applicative.*`
+| 9: An algebraic View on Monads | [`readerwriter`](src/main/scala/readerwriter/) | `testOnly readerwriter.*`
## Usage tips:
To keep your local solutions to the exercises when pulling from the repository,
diff --git a/src/main/scala/readerwriter/Randoms.scala b/src/main/scala/readerwriter/Randoms.scala
index a5cc3ea19aa9e84ea2a290e6c2bef32fa192d578..e1ff2cb040507304a6b781eaa7ba9b441ff7498e 100644
--- a/src/main/scala/readerwriter/Randoms.scala
+++ b/src/main/scala/readerwriter/Randoms.scala
@@ -1,19 +1,15 @@
package readerwriter
-import readerwriter.internal.State, State._
-import util._
+import readerwriter.internal.State, State.*
object Randoms:
def threeInts: State[RNG, (Int, Int, Int)] = ???
- /*@formatter:off*/
def randomInt: State[RNG, Int] = for
rng <- get[RNG]
(rng2, i) = rng.nextInt
_ <- set(rng2)
yield i
- /*@formatter:on*/
-
def nonNegativeInt: State[RNG, Int] = for
i <- randomInt
@@ -23,6 +19,8 @@ trait RNG:
def nextInt: (RNG, Int)
case class Simple(seed: Long) extends RNG:
+ /** Basically the same formula as in java.util.Random
+ * See https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/Random.html#next(int) */
def nextInt: (RNG, Int) =
val newSeed = (seed * 0x5DEECE66DL + 0xBL) & 0xFFFFFFFFFFFFL
val nextRNG = Simple(newSeed)
diff --git a/src/main/scala/readerwriter/Readers.scala b/src/main/scala/readerwriter/Readers.scala
index 18b7dc9cd8a99b8054b5305a92c8404d228f4ac6..eeae72fa4afca74c9d075a2cae120d79a414d7b7 100644
--- a/src/main/scala/readerwriter/Readers.scala
+++ b/src/main/scala/readerwriter/Readers.scala
@@ -2,8 +2,7 @@ package readerwriter
import java.time.LocalDate
-import readerwriter.internal.Reader, Reader._
-import util._
+import readerwriter.internal.Reader, Reader.*
final case class Request(
user: Option[String],
diff --git a/src/main/scala/readerwriter/Writers.scala b/src/main/scala/readerwriter/Writers.scala
index 3abbc1a184a37114d8c3ab91cfe1df74307cfa02..3f50ba9de0a9f6a734bfd865925ed50b1df8100c 100644
--- a/src/main/scala/readerwriter/Writers.scala
+++ b/src/main/scala/readerwriter/Writers.scala
@@ -1,9 +1,7 @@
package readerwriter
-import readerwriter.internal.Writer, Writer._
-import util._
-
+import readerwriter.internal.Writer, Writer.{*, given}
object Writers:
/* everything required to use tell and the monad operations
@@ -13,7 +11,6 @@ object Writers:
def collatzSearch(start: Int, limit: Int): Writer[List[String], Int] = ???
-
object CollatzWithoutWriter:
def collatzDepth(n: Int): (List[String], Int) =
if n == 1 then
diff --git a/src/main/scala/readerwriter/internal/Reader.scala b/src/main/scala/readerwriter/internal/Reader.scala
index e9a12b9e916d912e95728917fd33eb38656e62d6..f2d6e0c997f45832ea4ebe5beb4c3675e011d880 100644
--- a/src/main/scala/readerwriter/internal/Reader.scala
+++ b/src/main/scala/readerwriter/internal/Reader.scala
@@ -2,7 +2,7 @@ package readerwriter.internal
import applicative.Monad
-case class Reader[R, A](run: R => A)
+case class Reader[-R, A](run: R => A)
object Reader:
def ask[R]: Reader[R, R] = Reader(x => x)
diff --git a/src/main/scala/readerwriter/internal/State.scala b/src/main/scala/readerwriter/internal/State.scala
index ca0ae913b02084027fc5a98b8704d3696fd15ec8..b41c36e237ec0501a4c8b01eb0a1ee5e71e0bc52 100644
--- a/src/main/scala/readerwriter/internal/State.scala
+++ b/src/main/scala/readerwriter/internal/State.scala
@@ -8,6 +8,9 @@ import applicative.Monad
case class State[S, A] private (run: S => (S, A))
case object State:
+ def get[S]: State[S, S] = State(s => (s, s))
+ def set[S](s: S): State[S, Unit] = State(_ => (s, ()))
+
given stateMonad[S]: Monad[[a] =>> State[S, a]] with
def pure[A](a: A): State[S, A] = State(s => (s, a))
extension [A](fa: State[S, A])
@@ -15,6 +18,3 @@ case object State:
val (s1, a) = fa.run(s)
f(a).run(s1)
)
-
- def get[S]: State[S, S] = State(s => (s, s))
- def set[S](s: S): State[S, Unit] = State(_ => (s, ()))
diff --git a/src/main/scala/readerwriter/internal/Writer.scala b/src/main/scala/readerwriter/internal/Writer.scala
index 7e4e0b85637dbebc65393a10f966fbffb34f6a84..1a7ee8d064713c8d0acfca8377d7b7d28d565462 100644
--- a/src/main/scala/readerwriter/internal/Writer.scala
+++ b/src/main/scala/readerwriter/internal/Writer.scala
@@ -6,6 +6,7 @@ import applicative.Monad
final case class Writer[L, A](v: (L, A))
object Writer:
+
given [A]: Monoid[List[A]] with
def zero: List[Nothing] = List.empty
def combine(l1: List[A], l2: List[A]): List[A] = l1 ++ l2
diff --git a/src/main/scala/util/package.scala b/src/main/scala/util/package.scala
deleted file mode 100644
index b3402eacf8c76a175214803d7825f6a50bde07b2..0000000000000000000000000000000000000000
--- a/src/main/scala/util/package.scala
+++ /dev/null
@@ -1,6 +0,0 @@
-import applicative.Monad
-
-package object util:
- implicit class MonadOps[F[_] : Monad, A](fa: F[A]):
- def flatMap[B](f: A => F[B]): F[B] = implicitly[Monad[F]].flatMap(fa)(f)
- def map[B](f: A => B): F[B] = implicitly[Monad[F]].map(fa)(f)
diff --git a/src/test/scala/readerwriter/ReaderSpec.scala b/src/test/scala/readerwriter/ReaderSpec.scala
index bf036ac6b2d0291476e605bd7dbb2c33db4d39ab..78878e8a63b129f7318f87216c14c3365b2c964f 100644
--- a/src/test/scala/readerwriter/ReaderSpec.scala
+++ b/src/test/scala/readerwriter/ReaderSpec.scala
@@ -27,6 +27,6 @@ class ReaderSpec extends AnyFlatSpec with Matchers with AppendedClues with Pendi
}
"sayBye" should "contain the correct user name and date" in {
- Readers.sayBye.run(exampleRequest) shouldBe "Goodbye Mister X, today is 2019-06-26"
+ Readers.sayBye.run(exampleRequest) shouldBe "Goodbye Mister X, now is 2019-06-26"
}