From 5a1ff4130b217fba9bc3cd0def89da4970bf9143 Mon Sep 17 00:00:00 2001
From: Alexey Rykhalskiy <alexey.rykhalskiy@gmail.com>
Date: Thu, 19 Oct 2023 21:07:32 +0300
Subject: [PATCH] -- type lambda

---
 README.md                                     |  1 -
 .../scala/fwd/ForwardReferenceProblem.scala   | 29 +++++++++++++++++++
 ce3/src/main/scala/gas104/Htttp.scala         |  2 +-
 .../src/main/scala/advanced/TypeLambda1.scala |  1 +
 .../src/main/scala/advanced/TypeLambda3.scala | 28 ++++++++++++++++++
 project/CompilerOptions.scala                 |  1 +
 repositories.md                               | 12 ++++++++
 7 files changed, 72 insertions(+), 2 deletions(-)
 create mode 100644 ce3/src/main/scala/fwd/ForwardReferenceProblem.scala
 create mode 100644 plain2/src/main/scala/advanced/TypeLambda3.scala
 create mode 100644 repositories.md

diff --git a/README.md b/README.md
index 1fde9174..edc0f0fa 100644
--- a/README.md
+++ b/README.md
@@ -130,4 +130,3 @@ I thought I knew Scala...
   - circe
   - shapeless
 - kafka streams processing
-- 
\ No newline at end of file
diff --git a/ce3/src/main/scala/fwd/ForwardReferenceProblem.scala b/ce3/src/main/scala/fwd/ForwardReferenceProblem.scala
new file mode 100644
index 00000000..9ba3c6bb
--- /dev/null
+++ b/ce3/src/main/scala/fwd/ForwardReferenceProblem.scala
@@ -0,0 +1,29 @@
+package fwd
+
+object ForwardReferenceProblem extends App {
+
+  val x = y
+  val y = 5
+
+  println(s"x=$x")
+  println(s"y=$y")
+
+  /** compilation fails 1:
+    *
+    * def noProblem1() = {
+    *   val a = b
+    *   val b = 1
+    * }
+    *
+    */
+
+  /** compilation fails 1:
+    *
+    * def noProblem2() = for {
+    *   b <- Option(a)
+    *   a <- Option(1)
+    * } yield (a, b)
+    *
+    */
+
+}
diff --git a/ce3/src/main/scala/gas104/Htttp.scala b/ce3/src/main/scala/gas104/Htttp.scala
index 05e57920..418a4f84 100644
--- a/ce3/src/main/scala/gas104/Htttp.scala
+++ b/ce3/src/main/scala/gas104/Htttp.scala
@@ -128,7 +128,7 @@ object Htttp {
       case Some(data) =>
         data.traverse_ { x: Row =>
           val r    = URow.from(x)
-          val line = (r.dateTime, r.counter, r.delta)
+          val line = (r.dateTime.toLocalDate, r.counter, r.delta)
           Sync[F].delay(pprint.pprintln(line))
         }
       case None       =>
diff --git a/plain2/src/main/scala/advanced/TypeLambda1.scala b/plain2/src/main/scala/advanced/TypeLambda1.scala
index 2571cfc6..74f95c80 100644
--- a/plain2/src/main/scala/advanced/TypeLambda1.scala
+++ b/plain2/src/main/scala/advanced/TypeLambda1.scala
@@ -96,6 +96,7 @@ object TypeLambda1 extends App {
 
   object solution22 {
     def foo2[F[_, _], B](f: Functor[({ type ab[C] = F[B, C] })#ab]) = ???
+    //                              =============================
   }
 
   object solution23 {
diff --git a/plain2/src/main/scala/advanced/TypeLambda3.scala b/plain2/src/main/scala/advanced/TypeLambda3.scala
new file mode 100644
index 00000000..554cdc8a
--- /dev/null
+++ b/plain2/src/main/scala/advanced/TypeLambda3.scala
@@ -0,0 +1,28 @@
+package advanced
+
+object TypeLambda3 extends App {
+
+  // Functor has one `hole`
+  trait Functor[F[_]]
+
+  // MonadError has two `holes`
+  trait MonadError[F[_], E]
+
+  // Functor can be specified as a type bounds
+  class Repository1[F[_]: Functor]
+
+  // but MonadError can not
+
+  // we can introduce type alias
+  type MonadErrorThrowable[F[_]] = MonadError[F, Throwable]
+
+  // and use it
+  class Repository2[F[_]: MonadErrorThrowable]
+
+  // or use type lambda and not declare alias
+  class Repository3[F[_]: ({ type MET[f[_]] = MonadError[f, Throwable] })#MET]
+
+  // or use type lambda and not declare alias
+  class Repository4[F[_]: MonadError[*[_], Throwable]]
+
+}
diff --git a/project/CompilerOptions.scala b/project/CompilerOptions.scala
index 4b71b7fb..04946718 100644
--- a/project/CompilerOptions.scala
+++ b/project/CompilerOptions.scala
@@ -23,6 +23,7 @@ object CompilerOptions {
     warningsAsFatals, // ??? doesn't work as expected
     matchShouldBeExhaustive,
     lintDeprecation,
+    "-Xcheckinit",
     // "-Xlint:unsound-match",
     // "-Ypartial-unification", // by default since 2.13
     "-language:existentials",
diff --git a/repositories.md b/repositories.md
new file mode 100644
index 00000000..aad41ff2
--- /dev/null
+++ b/repositories.md
@@ -0,0 +1,12 @@
+### repositories
+
+- https://github.com/alexr007/learning-scalajs2.git
+- https://github.com/alexr007/learning-scalajs3.git
+- https://github.com/alexr007/learning-fullstack.git
+- https://github.com/alexr007/learning-doodle.git
+- https://github.com/alexr007/learning-chartreuse.git
+- https://github.com/alexr007/learning-chartreuse.git
+- https://github.com/alexr007/learning-tyrian.git
+- https://github.com/alexr007/learning-haskell.git
+- https://github.com/alexr007/learning-rust.git
+- 
\ No newline at end of file