.gitlab-ci.yml

@@ -26,7 +26,7 @@ grade:
   tags:
     - cs210
   image:
-    name: registry.gitlab.com/fnux/cs210-grading-images/progfun2-streams:20191030-43a7371aecb1bee74b8e4c3b0aba175f3ff4d0c6
+    name: registry.gitlab.com/fnux/cs210-grading-images/progfun2-codecs:20191027-dfbea8aed96096ed3af1cf1958549b97328d4c25
     entrypoint: [""]
   allow_failure: true
   before_script:

README.md

@@ -1,7 +1,6 @@
-# CS-210: Streams (Bloxorz)
-
+# CS-210: Codecs
 
 Please follow the [instructions from the main course
-respository](https://gitlab.epfl.ch/lamp/cs-210-functional-programming-2019/blob/master/week9/00-homework7.md).
+respository](https://gitlab.epfl.ch/lamp/cs-210-functional-programming-2019/blob/master/week11/00-homework8.md).
 
 Grading and submission details can be found [here](https://gitlab.epfl.ch/lamp/cs-210-functional-programming-2019/blob/master/week1/02-grading-and-submission.md).

build.sbt

@@ -1,12 +1,16 @@
 course := "progfun2"
-assignment := "streams"
+assignment := "codecs"
 name := course.value + "-" + assignment.value
-testSuite := "streams.BloxorzSuite"
+testSuite := "codecs.CodecsSuite"
 
 scalaVersion := "0.19.0-RC1"
-
-scalacOptions ++= Seq("-language:implicitConversions", "-deprecation")
-libraryDependencies += "com.novocode" % "junit-interface" % "0.11" % Test
-libraryDependencies += ("org.scalacheck" %% "scalacheck" % "1.14.2").withDottyCompat(scalaVersion.value)
+scalacOptions ++= Seq("-deprecation")
+libraryDependencies ++= Seq(
+  ("org.scalacheck" %% "scalacheck" % "1.14.2" % Test).withDottyCompat(scalaVersion.value),
+  ("org.typelevel" %% "jawn-parser" % "0.14.2").withDottyCompat(scalaVersion.value),
+  "com.novocode" % "junit-interface" % "0.11" % Test
+)
 
 testOptions in Test += Tests.Argument(TestFrameworks.JUnit, "-a", "-v", "-s")
+
+initialCommands in console := """import codecs.{_, given}"""

src/main/scala/codecs/codecs.scala

@@ -0,0 +1,283 @@
+package codecs
+
+/**
+  * A data type modeling JSON values.
+  *
+  * For example, the `42` integer JSON value can be modeled as `Json.Num(42)`
+  */
+sealed trait Json {
+  /**
+   * Try to decode this JSON value into a value of type `A` by using
+   * the given decoder.
+   *
+   * Note that you have to explicitly fix `A` type parameter when you call the method:
+   *
+   * {{{
+   *   someJsonValue.decodeAs[User] // OK
+   *   someJsonValue.decodeAs       // Wrong!
+   * }}}
+   */
+  def decodeAs[A](given decoder: Decoder[A]): Option[A] = decoder.decode(this)
+}
+
+object Json {
+  /** The JSON `null` value */
+  case object Null extends Json
+  /** JSON boolean values */
+  case class Bool(value: Boolean) extends Json
+  /** JSON numeric values */
+  case class Num(value: BigDecimal) extends Json
+  /** JSON string values */
+  case class Str(value: String) extends Json
+  /** JSON objects */
+  case class Obj(fields: Map[String, Json]) extends Json
+  /** JSON arrays */
+  case class Arr(items: List[Json]) extends Json
+}
+
+/**
+  * A type class that turns a value of type `A` into its JSON representation.
+  */
+trait Encoder[-A] {
+
+  def encode(value: A): Json
+
+    /**
+    * Transforms this `Encoder[A]` into an `Encoder[B]`, given a transformation function
+    * from `B` to `A`.
+    *
+    * For instance, given a `Encoder[String]`, we can get an `Encoder[UUID]`:
+    *
+    * {{{
+    *   def uuidEncoder(given stringEncoder: Encoder[String]): Encoder[UUID] =
+    *     stringEncoder.transform[UUID](uuid => uuid.toString)
+    * }}}
+    *
+    * This operation is also known as ?contramap?.
+    */
+  def transform[B](f: B => A): Encoder[B] =
+    Encoder.fromFunction[B](value => this.encode(f(value)))  
+}
+
+object Encoder extends GivenEncoders {
+
+  /**
+   * Convenient method for creating an instance of encoder from a function `f`
+   */
+  def fromFunction[A](f: A => Json) = new Encoder[A] {
+    def encode(value: A): Json = f(value)
+  }
+
+}
+
+trait GivenEncoders {
+
+  /** An encoder for the `Unit` value */
+  given Encoder[Unit] = Encoder.fromFunction(_ => Json.Null)
+
+  /** An encoder for `Int` values */
+  given Encoder[Int] = Encoder.fromFunction(n => Json.Num(BigDecimal(n)))
+
+  /** An encoder for `String` values */
+  given Encoder[String] =
+    Encoder.fromFunction(str => Json.Str(str))
+
+  /** An encoder for `Boolean` values */
+  given Encoder[Boolean] =
+    Encoder.fromFunction(v => Json.Bool(v))
+
+  /**
+    * Encodes a list of values of type `A` into a JSON array containing
+    * the list elements encoded with the given `encoder`
+    */
+  given [A](given encoder: Encoder[A]): Encoder[List[A]] =
+    Encoder.fromFunction(as => Json.Arr(as.map(encoder.encode)))
+
+}
+
+/**
+  * A specialization of `Encoder` that returns JSON objects only
+  */
+trait ObjectEncoder[-A] extends Encoder[A] {
+  // Refines the encoding result to `Json.Obj`
+  def encode(value: A): Json.Obj
+
+  /**
+    * Combines `this` encoder with `that` encoder.
+    * Returns an encoder producing a JSON object containing both
+    * fields of `this` encoder and fields of `that` encoder.
+    */
+  def zip[B](that: ObjectEncoder[B]): ObjectEncoder[(A, B)] =
+    ObjectEncoder.fromFunction { (a, b) =>
+      Json.Obj(this.encode(a).fields ++ that.encode(b).fields)
+    }
+}
+
+object ObjectEncoder {
+
+  /**
+    * Convenient method for creating an instance of object encoder from a function `f`
+    */
+  def fromFunction[A](f: A => Json.Obj): ObjectEncoder[A] = new ObjectEncoder[A] {
+    def encode(value: A): Json.Obj = f(value)
+  }
+
+  /**
+    * An encoder for values of type `A` that produces a JSON object with one field
+    * named according to the supplied `name` and containing the encoded value.
+    */
+  def field[A](name: String)(given encoder: Encoder[A]): ObjectEncoder[A] =
+    ObjectEncoder.fromFunction(a => Json.Obj(Map(name -> encoder.encode(a))))
+
+}
+
+/**
+  * The dual of an encoder. Decodes a serialized value into its initial type `A`.
+  */
+trait Decoder[+A] {
+  /**
+    * @param data The data to de-serialize
+    * @return The decoded value wrapped in `Some`, or `None` if decoding failed
+    */
+  def decode(data: Json): Option[A]
+
+  /**
+    * Combines `this` decoder with `that` decoder.
+    * Returns a decoder that invokes both `this` decoder and `that`
+    * decoder and returns a pair of decoded value in case both succeed,
+    * or `None` if at least one failed.
+    */
+  def zip[B](that: Decoder[B]): Decoder[(A, B)] =
+    Decoder.fromFunction { json =>
+      this.decode(json).zip(that.decode(json))
+    }
+
+  /**
+    * Transforms this `Decoder[A]` into a `Decoder[B]`, given a transformation function
+    * from `A` to `B`.
+    *
+    * This operation is also known as ?map?.
+    */
+  def transform[B](f: A => B): Decoder[B] =
+    Decoder.fromFunction(json => this.decode(json).map(f))
+}
+
+object Decoder extends GivenDecoders {
+
+  /**
+    * Convenient method to build a decoder instance from a function `f`
+    */
+  def fromFunction[A](f: Json => Option[A]): Decoder[A] = new Decoder[A] {
+    def decode(data: Json): Option[A] = f(data)
+  }
+
+  /**
+    * Alternative method for creating decoder instances
+    */
+  def fromPartialFunction[A](pf: PartialFunction[Json, A]): Decoder[A] =
+    fromFunction(pf.lift)
+
+}
+
+trait GivenDecoders {
+
+  /** A decoder for the `Unit` value */
+  given Decoder[Unit] =
+    Decoder.fromPartialFunction { case Json.Null => () }
+
+  /** A decoder for `Int` values. Hint: use the `isValidInt` method of `BigDecimal`. */
+  // TODO Define a given `Decoder[Int]` instance
+  given Decoder[Int] = 
+    Decoder.fromFunction{ case Json.Num(v) => if v.isValidInt then Some(v.intValue) else None
+                          case _ => None}
+
+  /** A decoder for `String` values */
+  // TODO Define a given `Decoder[String]` instance
+  given Decoder[String] = 
+    Decoder.fromPartialFunction{ case Json.Str(str) => str}
+
+  /** A decoder for `Boolean` values */
+  // TODO Define a given `Decoder[Boolean]` instance
+  given Decoder[Boolean] = 
+    Decoder.fromPartialFunction{ case Json.Bool(v) => v}
+  /**
+    * A decoder for JSON arrays. It decodes each item of the array
+    * using the given `decoder`. The resulting decoder succeeds only
+    * if all the JSON array items are successfully decoded.
+    */
+  given [A](given decoder: Decoder[A]): Decoder[List[A]] =
+    Decoder.fromFunction {
+      case Json.Arr(items: List[Json]) => Some(items.map(v => decoder.decode(v).get))
+      case _ => None
+    }
+
+  /**
+    * A decoder for JSON objects. It decodes the value of a field of
+    * the supplied `name` using the given `decoder`.
+    */
+  def field[A](name: String)(given decoder: Decoder[A]): Decoder[A] =
+    Decoder.fromFunction{
+      case Json.Obj(field: Map[String, Json]) => decoder.decode(field.get(name).get)
+      case _ => None
+    }
+
+}
+
+case class Person(name: String, age: Int)
+
+object Person extends PersonCodecs
+
+trait PersonCodecs {
+
+  /** The encoder for `Person` */
+  given Encoder[Person] =
+    ObjectEncoder.field[String]("name")
+      .zip(ObjectEncoder.field[Int]("age"))
+      .transform[Person](user => (user.name, user.age))
+
+  /** The corresponding decoder for `Person` */
+  given Decoder[Person] ={
+    Decoder.field[String]("name").zip(Decoder.field[Int]("age")).transform[Person](user => Person(user._1, user._2))
+    }
+
+}
+
+case class Contacts(people: List[Person])
+
+object Contacts extends ContactsCodecs
+
+trait ContactsCodecs {
+
+  // TODO Define the encoder and the decoder for `Contacts`
+  // The JSON representation of a value of type `Contacts` should be
+  // a JSON object with a single field named ?people? containing an
+  // array of values of type `Person` (reuse the `Person` codecs)
+  given Encoder[Contacts] = 
+    ObjectEncoder.field[List[Person]]("people").transform[Contacts](c => c.people)
+
+  given Decoder[Contacts] = 
+    Decoder.field[List[Person]]("people").transform[Contacts](p => Contacts(p))
+
+}
+
+// In case you want to try your code, here is a simple `Main`
+// that can be used as a starting point. Otherwise, you can use
+// the REPL (use the `console` sbt task).
+object Main {
+
+  def main(args: Array[String]): Unit = {
+    println(renderJson(42))
+    println(renderJson("foo"))
+
+    val maybeJsonString = parseJson(""" "foo" """)
+    val maybeJsonObj    = parseJson(""" { "name": "Alice", "age": 42 } """)
+    val maybeJsonObj2   = parseJson(""" { "name": "Alice", "age": "42" } """)
+    // Uncomment the following lines as you progress in the assignment
+    println(maybeJsonString.flatMap(_.decodeAs[Int]))
+    println(maybeJsonString.flatMap(_.decodeAs[String]))
+    println(maybeJsonObj.flatMap(_.decodeAs[Person]))
+    println(maybeJsonObj2.flatMap(_.decodeAs[Person]))
+    println(renderJson(Person("Bob", 66)))
+  }
+
+}

src/main/scala/codecs/json.scala

@@ -0,0 +1,74 @@
+package codecs
+
+import org.typelevel.jawn.{ Parser, SimpleFacade }
+import scala.collection.mutable
+import scala.util.Try
+
+// Utility methods that decode values from `String` JSON blobs, and
+// render values to `String` JSON blobs
+
+/**
+ * Parse a JSON document contained in a `String` value into a `Json` value, returns
+ * `None` in case the supplied `s` value is not a valid JSON document.
+ */
+def parseJson(s: String): Option[Json] = Parser.parseFromString[Json](s).toOption
+
+/**
+  * Parse the JSON value from the supplied `s` parameter, and then try to decode
+  * it as a value of type `A` using the given `decoder`.
+  *
+  * Returns `None` if JSON parsing failed, or if decoding failed.
+  */
+def parseAndDecode[A](s: String)(given decoder: Decoder[A]): Option[A] =
+  for {
+    json <- parseJson(s)
+    a    <- decoder.decode(json)
+  } yield a
+
+/**
+  * Render the supplied `value` into JSON using the given `encoder`.
+  */
+def renderJson[A](value: A)(given encoder: Encoder[A]): String =
+  render(encoder.encode(value))
+
+private def render(json: Json): String = json match {
+  case Json.Null    => "null"
+  case Json.Bool(b) => b.toString
+  case Json.Num(n)  => n.toString
+  case Json.Str(s)  => renderString(s)
+  case Json.Arr(vs) => vs.map(render).mkString("[", ",", "]")
+  case Json.Obj(vs) => vs.map { case (k, v) => s"${renderString(k)}:${render(v)}" }.mkString("{", ",", "}")
+}
+
+private def renderString(s: String): String = {
+  val sb = new StringBuilder
+  sb.append('"')
+  var i = 0
+  val len = s.length
+  while (i < len) {
+    s.charAt(i) match {
+      case '"' => sb.append("\\\"")
+      case '\\' => sb.append("\\\\")
+      case '\b' => sb.append("\\b")
+      case '\f' => sb.append("\\f")
+      case '\n' => sb.append("\\n")
+      case '\r' => sb.append("\\r")
+      case '\t' => sb.append("\\t")
+      case c =>
+        if (c < ' ') sb.append("\\u%04x" format c.toInt)
+        else sb.append(c)
+    }
+    i += 1
+  }
+  sb.append('"').toString
+}
+
+given SimpleFacade[Json] {
+  def jnull() = Json.Null
+  def jtrue() = Json.Bool(true)
+  def jfalse() = Json.Bool(false)
+  def jnum(s: CharSequence, decIndex: Int, expIndex: Int) = Json.Num(BigDecimal(s.toString))
+  def jstring(s: CharSequence) = Json.Str(s.toString)
+  def jarray(vs: List[Json]) = Json.Arr(vs)
+  def jobject(vs: Map[String, Json]) = Json.Obj(vs)
+}

src/main/scala/streams/Bloxorz.scala

@@ -1,49 +0,0 @@
-package streams
-
-/**
- * A main object that can be used to execute the Bloxorz solver
- */
-object Bloxorz extends App {
-
-  /**
-   * A level constructed using the `InfiniteTerrain` trait which defines
-   * the terrain to be valid at every position.
-   */
-  object InfiniteLevel extends Solver with InfiniteTerrain {
-    val startPos = Pos(1,3)
-    val goal = Pos(5,8)
-  }
-
-  println(InfiniteLevel.solution)
-
-  /**
-   * A simple level constructed using the StringParserTerrain
-   */
-  abstract class Level extends Solver with StringParserTerrain
-
-  object Level0 extends Level {
-    val level =
-      """------
-        |--ST--
-        |--oo--
-        |--oo--
-        |------""".stripMargin
-  }
-
-  println(Level0.solution)
-
-  /**
-   * Level 1 of the official Bloxorz game
-   */
-  object Level1 extends Level {
-    val level =
-      """ooo-------
-        |oSoooo----
-        |ooooooooo-
-        |-ooooooooo
-        |-----ooToo
-        |------ooo-""".stripMargin
-  }
-
-  println(Level1.solution)
-}

src/main/scala/streams/GameDef.scala

@@ -1,170 +0,0 @@
-package streams
-
-/**
- * This trait represents the layout and building blocks of the game
- */
-trait GameDef {
-
-  /**
-   * The case class `Pos` encodes positions in the terrain.
-   *
-   * IMPORTANT NOTE
-   *  - The `row` coordinate denotes the position on the vertical axis
-   *  - The `col` coordinate is used for the horizontal axis
-   *  - The coordinates increase when moving down and right
-   *
-   * Illustration:
-   *
-   *     0 1 2 3   <- col axis
-   *   0 o o o o
-   *   1 o o o o
-   *   2 o # o o    # is at position Pos(2, 1)
-   *   3 o o o o
-   *
-   *   ^
-   *   |
-   *
-   *   row axis
-   */
-  case class Pos(row: Int, col: Int) {
-    /** The position obtained by changing the `row` coordinate by `d` */
-    def deltaRow(d: Int): Pos = copy(row = row + d)
-
-    /** The position obtained by changing the `col` coordinate by `d` */
-    def deltaCol(d: Int): Pos = copy(col = col + d)
-  }
-
-  /**
-   * The position where the block is located initially.
-   *
-   * This value is left abstract, it will be defined in concrete
-   * instances of the game.
-   */
-  def startPos: Pos
-
-  /**
-   * The target position where the block has to go.
-   * This value is left abstract.
-   */
-  def goal: Pos
-
-  /**
-   * The terrain is represented as a function from positions to
-   * booleans. The function returns `true` for every position that
-   * is inside the terrain.
-   *
-   * As explained in the documentation of class `Pos`, the `row` axis
-   * is the vertical one and increases from top to bottom.
-   */
-  type Terrain = Pos => Boolean
-
-
-  /**
-   * The terrain of this game. This value is left abstract.
-   */
-  def terrain: Terrain
-
-
-  /**
-   * In Bloxorz, we can move left, right, Up or down.
-   * These moves are encoded as case objects.
-   */
-  sealed abstract class Move
-  case object Left  extends Move
-  case object Right extends Move
-  case object Up    extends Move
-  case object Down  extends Move
-
-  /**
-   * This function returns the block at the start position of
-   * the game.
-   */
-  def startBlock: Block = Block(startPos, startPos)
-
-
-  /**
-   * A block is represented by the position of the two cubes that
-   * it consists of. We make sure that `b1` is lexicographically
-   * smaller than `b2`.
-   */
-  case class Block(b1: Pos, b2: Pos) {
-
-    // checks the requirement mentioned above
-    require(b1.row <= b2.row && b1.col <= b2.col, s"Invalid block position: b1=$b1, b2=$b2")
-
-    /**
-     * Returns a block where the `row` coordinates of `b1` and `b2` are
-     * changed by `d1` and `d2`, respectively.
-     */
-    def deltaRow(d1: Int, d2: Int) = Block(b1.deltaRow(d1), b2.deltaRow(d2))
-
-    /**
-     * Returns a block where the `col` coordinates of `b1` and `b2` are
-     * changed by `d1` and `d2`, respectively.
-     */
-    def deltaCol(d1: Int, d2: Int) = Block(b1.deltaCol(d1), b2.deltaCol(d2))
-
-
-    /** The block obtained by moving left */
-    def left =
-      if isStanding then
-        deltaCol(-2, -1)
-      else if b1.row == b2.row then
-        deltaCol(-1, -2)
-      else
-        deltaCol(-1, -1)
-
-    /** The block obtained by moving right */
-    def right =
-      if isStanding then
-        deltaCol(1, 2)
-      else if b1.row == b2.row then
-        deltaCol(2, 1)
-      else
-        deltaCol(1, 1)
-
-    /** The block obtained by moving up */
-    def up =
-      if isStanding then
-        deltaRow(-2, -1)
-      else if b1.row == b2.row then
-        deltaRow(-1, -1)
-      else
-        deltaRow(-1, -2)
-
-    /** The block obtained by moving down */
-    def down =
-      if isStanding then
-        deltaRow(1, 2)
-      else if b1.row == b2.row then
-        deltaRow(1, 1)
-      else
-        deltaRow(2, 1)
-
-
-    /**
-     * Returns the list of blocks that can be obtained by moving
-     * the current block, together with the corresponding move.
-     */
-    def neighbors: List[(Block, Move)] = 
-      List((left, Left), (right, Right), (up, Up), (down, Down))
-
-    /**
-     * Returns the list of positions reachable from the current block
-     * which are inside the terrain.
-     */
-    def legalNeighbors: List[(Block, Move)] = neighbors.filter{
-      case (b, _) => b.isLegal
-    }
-
-    /**
-     * Returns `true` if the block is standing.
-     */
-    def isStanding: Boolean = b1 == b2
-
-    /**
-     * Returns `true` if the block is entirely inside the terrain.
-     */
-    def isLegal: Boolean = terrain(b1) && terrain(b2)
-  }
-}

src/main/scala/streams/InfiniteTerrain.scala

@@ -1,15 +0,0 @@
-package streams
-
-/**
- * This trait defines an infinite terrain, where the block can
- * go on any position.
- *
- * It keeps the `startPos` and the `goal` positions abstract.
- *
- * Using this trait is useful for testing. It can be used to find
- * the shortest path between two positions without terrain
- * restrictions.
- */
-trait InfiniteTerrain extends GameDef {
-  val terrain: Terrain = (pos: Pos) => true
-}

src/main/scala/streams/Solver.scala

@@ -1,103 +0,0 @@
-package streams
-
-/**
- * This component implements the solver for the Bloxorz game
- */
-trait Solver extends GameDef {
-
-  /**
-   * Returns `true` if the block `b` is at the final position
-   */
-  def done(b: Block): Boolean = b.b1 == goal && b.isStanding
-
-  /**
-   * This function takes two arguments: the current block `b` and
-   * a list of moves `history` that was required to reach the
-   * position of `b`.
-   *
-   * The `head` element of the `history` list is the latest move
-   * that was executed, i.e. the last move that was performed for
-   * the block to end up at position `b`.
-   *
-   * The function returns a lazy list of pairs: the first element of
-   * the each pair is a neighboring block, and the second element
-   * is the augmented history of moves required to reach this block.
-   *
-   * It should only return valid neighbors, i.e. block positions
-   * that are inside the terrain.
-   */
-  def neighborsWithHistory(b: Block, history: List[Move]): LazyList[(Block, List[Move])] = {
-    lazy val result = b.legalNeighbors.map({pair=> (pair._1, pair._2 +: history)})
-    result.to(LazyList)
-  }
-
-  /**
-   * This function returns the list of neighbors without the block
-   * positions that have already been explored. We will use it to
-   * make sure that we don't explore circular paths.
-   */
-  def newNeighborsOnly(neighbors: LazyList[(Block, List[Move])],
-                       explored: Set[Block]): LazyList[(Block, List[Move])] = {
-                         neighbors.filter(n => !explored.contains(n._1))
-                       }
-
-  /**
-   * The function `from` returns the lazy list of all possible paths
-   * that can be followed, starting at the `head` of the `initial`
-   * lazy list.
-   *
-   * The blocks in the lazy list `initial` are sorted by ascending path
-   * length: the block positions with the shortest paths (length of
-   * move list) are at the head of the lazy list.
-   *
-   * The parameter `explored` is a set of block positions that have
-   * been visited before, on the path to any of the blocks in the
-   * lazy list `initial`. When search reaches a block that has already
-   * been explored before, that position should not be included a
-   * second time to avoid cycles.
-   *
-   * The resulting lazy list should be sorted by ascending path length,
-   * i.e. the block positions that can be reached with the fewest
-   * amount of moves should appear first in the lazy list.
-   *
-   * Note: the solution should not look at or compare the lengths
-   * of different paths - the implementation should naturally
-   * construct the correctly sorted lazy list.
-   */
-  def from(initial: LazyList[(Block, List[Move])],
-           explored: Set[Block]): LazyList[(Block, List[Move])] = {
-            if (initial.isEmpty) LazyList.empty
-            else {
-              val more = for {
-                pair <- initial
-                next <- newNeighborsOnly (neighborsWithHistory(pair._1, pair._2), explored)
-           } yield next
-           initial #::: from(more, explored ++ (more.map(_._1)))
-          }
-         }
-
-
-  /**
-   * The lazy list of all paths that begin at the starting block.
-   */
-  lazy val pathsFromStart: LazyList[(Block, List[Move])] = from(neighborsWithHistory(startBlock, List[Move]()), Set(startBlock))
-
-  /**
-   * Returns a lazy list of all possible pairs of the goal block along
-   * with the history how it was reached.
-   */
-  lazy val pathsToGoal: LazyList[(Block, List[Move])] = pathsFromStart.filter({case (b, m) => done(b)})
-
-  /**
-   * The (or one of the) shortest sequence(s) of moves to reach the
-   * goal. If the goal cannot be reached, the empty list is returned.
-   *
-   * Note: the `head` element of the returned list should represent
-   * the first move that the player should perform from the starting
-   * position.
-   */
-  lazy val solution: List[Move] = pathsToGoal.headOption match {
-    case None => List.empty
-    case Some(pair) => (pair._2).reverse
-  }
-}

src/main/scala/streams/StringParserTerrain.scala

@@ -1,83 +0,0 @@
-package streams
-
-/**
- * This component implements a parser to define terrains from a
- * graphical ASCII representation.
- *
- * When mixing in that component, a level can be defined by
- * defining the field `level` in the following form:
- *
- *   val level =
- *     """------
- *       |--ST--
- *       |--oo--
- *       |--oo--
- *       |------""".stripMargin
- *
- * - The `-` character denotes parts which are outside the terrain
- * - `o` denotes fields which are part of the terrain
- * - `S` denotes the start position of the block (which is also considered
-     inside the terrain)
- * - `T` denotes the final position of the block (which is also considered
-     inside the terrain)
- *
- * In this example, the first and last lines could be omitted, and
- * also the columns that consist of `-` characters only.
- */
-trait StringParserTerrain extends GameDef {
-
-  /**
-   * A ASCII representation of the terrain. This field should remain
-   * abstract here.
-   */
-  val level: String
-
-  /**
-   * This method returns terrain function that represents the terrain
-   * in `levelVector`. The vector contains parsed version of the `level`
-   * string. For example, the following level
-   *
-   *   val level =
-   *     """ST
-   *       |oo
-   *       |oo""".stripMargin
-   *
-   * is represented as
-   *
-   *   Vector(Vector('S', 'T'), Vector('o', 'o'), Vector('o', 'o'))
-   *
-   * The resulting function should return `true` if the position `pos` is
-   * a valid position (not a '-' character) inside the terrain described
-   * by `levelVector`.
-   */
-  def terrainFunction(levelVector: Vector[Vector[Char]]): Pos => Boolean = {
-    case Pos(x,y) => (for{
-      row <- levelVector.lift(x)
-      ch <- row.lift(y)
-      if(ch != '-')
-    } yield ch).isDefined
-  }
-
-  /**
-   * This function should return the position of character `c` in the
-   * terrain described by `levelVector`. You can assume that the `c`
-   * appears exactly once in the terrain.
-   *
-   * Hint: you can use the functions `indexWhere` and / or `indexOf` of the
-   * `Vector` class
-   */
-  def findChar(c: Char, levelVector: Vector[Vector[Char]]): Pos = {
-    val ys = levelVector.map(_.indexOf(c))
-    val x = ys.indexWhere(_ >= 0)
-
-    Pos(x, ys(x))
-  }
-
-  private lazy val vector: Vector[Vector[Char]] =
-    Vector(level.split("\r?\n").map(str => Vector(str: _*)).toIndexedSeq: _*)
-
-  lazy val terrain: Terrain = terrainFunction(vector)
-  lazy val startPos: Pos = findChar('S', vector)
-  lazy val goal: Pos = findChar('T', vector)
-
-}

src/test/scala/codecs/CodecsSuite.scala

@@ -0,0 +1,115 @@
+package codecs
+
+import org.scalacheck
+import org.scalacheck.{ Gen, Prop }
+import org.scalacheck.Prop.propBoolean
+import org.junit.{ Assert, Test }
+import scala.reflect.ClassTag
+
+class CodecsSuite extends GivenEncoders, GivenDecoders, PersonCodecs, ContactsCodecs, TestEncoders, TestDecoders {
+
+  def checkProperty(prop: Prop): Unit = {
+    val result = scalacheck.Test.check(scalacheck.Test.Parameters.default, prop)
+    def fail(labels: Set[String], fallback: String): Nothing =
+      if labels.isEmpty then throw new AssertionError(fallback)
+      else throw new AssertionError(labels.mkString(". "))
+    result.status match {
+      case scalacheck.Test.Passed | _: scalacheck.Test.Proved => ()
+      case scalacheck.Test.Failed(_, labels)                  => fail(labels, "A property failed.")
+      case scalacheck.Test.PropException(_, e, labels)        => fail(labels, s"An exception was thrown during property evaluation: $e.")
+      case scalacheck.Test.Exhausted                          => fail(Set.empty, "Unable to generate data.")
+    }
+  }
+
+  /**
+    * Check that a value of an arbitrary type `A` can be encoded and then successfully
+    * decoded with the given pair of encoder and decoder.
+    */
+  def encodeAndThenDecodeProp[A](a: A)(given encA: Encoder[A], decA: Decoder[A]): Prop = {
+    val maybeDecoded = decA.decode(encA.encode(a))
+    maybeDecoded.contains(a) :| s"Encoded value '$a' was not successfully decoded. Got '$maybeDecoded'."
+  }
+
+  @Test def `it is possible to encode and decode the 'Unit' value (0pts)`(): Unit = {
+    checkProperty(Prop.forAll((unit: Unit) => encodeAndThenDecodeProp(unit)))
+  }
+
+  @Test def `it is possible to encode and decode 'Int' values (1pt)`(): Unit = {
+    checkProperty(Prop.forAll((x: Int) => encodeAndThenDecodeProp(x)))
+  }
+
+  @Test def `the 'Int' decoder should reject invalid 'Int' values (2pts)`(): Unit = {
+    val decoded = summon[Decoder[Int]].decode(Json.Num(4.2))
+    assert(decoded.isEmpty, "decoding 4.2 as an integer value should fail")
+  }
+
+  @Test def `a 'String' value should be encoded as a JSON string (1pt)`(): Unit = {
+    assert(summon[Encoder[String]].encode("foo") == Json.Str("foo"))
+  }
+
+  @Test def `it is possible to encode and decode 'String' values (1pt)`(): Unit = {
+    checkProperty(Prop.forAll((s: String) => encodeAndThenDecodeProp(s)))
+  }
+
+  @Test def `a 'Boolean' value should be encoded as a JSON boolean (1pt)`(): Unit = {
+    val encoder = summon[Encoder[Boolean]]
+    assert(encoder.encode(true) == Json.Bool(true))
+    assert(encoder.encode(false) == Json.Bool(false))
+  }
+
+  @Test def `it is possible to encode and decode 'Boolean' values (1pt)`(): Unit = {
+    checkProperty(Prop.forAll((b: Boolean) => encodeAndThenDecodeProp(b)))
+  }
+
+  @Test def `a 'List[A]' value should be encoded as a JSON array (0pts)`(): Unit = {
+    val xs = 1 :: 2 :: Nil
+    val encoder = summon[Encoder[List[Int]]]
+    assert(encoder.encode(xs) == Json.Arr(List(Json.Num(1), Json.Num(2))))
+  }
+
+  @Test def `it is possible to encode and decode lists (5pts)`(): Unit = {
+    checkProperty(Prop.forAll((xs: List[Int]) => encodeAndThenDecodeProp(xs)))
+  }
+
+  @Test def `a 'Person' value should be encoded as a JSON object (1pt)`(): Unit = {
+    val person = Person("Alice", 42)
+    val json = Json.Obj(Map("name" -> Json.Str("Alice"), "age" -> Json.Num(42)))
+    val encoder = summon[Encoder[Person]]
+    assert(encoder.encode(person) == json)
+  }
+
+  @Test def `it is possible to encode and decode people (4pts)`(): Unit = {
+    checkProperty(Prop.forAll((s: String, x: Int) => encodeAndThenDecodeProp(Person(s, x))))
+  }
+  
+  @Test def `a 'Contacts' value should be encoded as a JSON object (1pt)`(): Unit = {
+    val contacts = Contacts(List(Person("Alice", 42)))
+    val json = Json.Obj(Map("people" ->
+      Json.Arr(List(Json.Obj(Map("name" -> Json.Str("Alice"), "age" -> Json.Num(42)))))
+    ))
+    val encoder = summon[Encoder[Contacts]]
+    assert(encoder.encode(contacts) == json)
+  }
+
+  @Test def `it is possible to encode and decode contacts (4pts)`(): Unit = {
+    val peopleGenerator = Gen.listOf(Gen.resultOf((s: String, x: Int) => Person(s, x)))
+    checkProperty(Prop.forAll(peopleGenerator)(people => encodeAndThenDecodeProp(Contacts(people))))
+  }
+
+}
+
+trait TestEncoders extends EncoderFallbackInstance
+
+trait EncoderFallbackInstance {
+
+  given [A](given ct: ClassTag[A]): Encoder[A] = throw new AssertionError(s"No given instance of `Encoder[${ct.runtimeClass.getSimpleName}]`")
+
+}
+
+trait TestDecoders extends DecoderFallbackInstance
+
+trait DecoderFallbackInstance {
+
+  given [A](given ct: ClassTag[A]): Decoder[A] = throw new AssertionError(s"No given instance of `Decoder[${ct.runtimeClass.getSimpleName}]")
+
+}

src/test/scala/streams/BloxorzSuite.scala

@@ -1,74 +0,0 @@
-package streams
-
-import org.junit._
-import org.junit.Assert.assertEquals
-
-import Bloxorz._
-
-class BloxorzSuite {
-  trait SolutionChecker extends GameDef with Solver with StringParserTerrain {
-    /**
-     * This method applies a list of moves `ls` to the block at position
-     * `startPos`. This can be used to verify if a certain list of moves
-     * is a valid solution, i.e. leads to the goal.
-     */
-    def solve(ls: List[Move]): Block =
-      ls.foldLeft(startBlock) { case (block, move) =>
-        require(block.isLegal) // The solution must always lead to legal blocks
-        move match
-          case Left => block.left
-          case Right => block.right
-          case Up => block.up
-          case Down => block.down
-      }
-  }
-
-  trait Level1 extends SolutionChecker {
-      /* terrain for level 1*/
-
-    val level =
-    """ooo-------
-      |oSoooo----
-      |ooooooooo-
-      |-ooooooooo
-      |-----ooToo
-      |------ooo-""".stripMargin
-
-    val optsolution = List(Right, Right, Down, Right, Right, Right, Down)
-  }
-
-
-  @Test def `terrain function level 1 (10pts)`: Unit =
-    new Level1 {
-      assert(terrain(Pos(0,0)), "0,0")
-      assert(terrain(Pos(1,1)), "1,1") // start
-      assert(terrain(Pos(4,7)), "4,7") // goal
-      assert(terrain(Pos(5,8)), "5,8")
-      assert(!terrain(Pos(5,9)), "5,9")
-      assert(terrain(Pos(4,9)), "4,9")
-      assert(!terrain(Pos(6,8)), "6,8")
-      assert(!terrain(Pos(4,11)), "4,11")
-      assert(!terrain(Pos(-1,0)), "-1,0")
-      assert(!terrain(Pos(0,-1)), "0,-1")
-    }
-
-  @Test def `find char level 1 (10pts)`: Unit =
-    new Level1 {
-      assertEquals(Pos(1, 1), startPos)
-    }
-
-
-  @Test def `optimal solution for level 1 (5pts)`: Unit =
-    new Level1 {
-      assertEquals(Block(goal, goal), solve(solution))
-    }
-
-
-  @Test def `optimal solution length for level 1 (5pts)`: Unit =
-    new Level1 {
-      assertEquals(optsolution.length, solution.length)
-    }
-
-
-  @Rule def individualTestTimeout = new org.junit.rules.Timeout(10 * 1000)
-}