From bd1be196a879240379a3a6df143e8b019815cf08 Mon Sep 17 00:00:00 2001
From: Alexandre Moreno <alexmorenocano@gmail.com>
Date: Sun, 7 Jan 2024 10:15:57 +0100
Subject: [PATCH] improve type inference of NonDet handlers

---
 core/src/main/scala/evidence/effect/NonDet.scala | 13 ++++++++++++-
 examples/src/main/scala/Example.scala            | 14 +++++++-------
 examples/src/main/scala/Parse.scala              |  8 ++------
 3 files changed, 21 insertions(+), 14 deletions(-)

diff --git a/core/src/main/scala/evidence/effect/NonDet.scala b/core/src/main/scala/evidence/effect/NonDet.scala
index 9b52dea..cbc120e 100644
--- a/core/src/main/scala/evidence/effect/NonDet.scala
+++ b/core/src/main/scala/evidence/effect/NonDet.scala
@@ -5,6 +5,8 @@ import cats.Alternative
 import cats.Monad
 import cats.implicits._
 import evidence.Ctx.In
+import cats.Foldable
+import cats.MonoidK
 
 type NonDet = [E, Ans] =>> NonDet.Syn[E, Ans]
 
@@ -33,7 +35,11 @@ object NonDet:
       NonDet.choose.ifM(x, y)
   }
 
-  def allResults[E, A, F[_]](using
+  def choice[E, A, G[_]](
+      ps: G[Eff[E, A]]
+  )(using G: Foldable[G], F: MonoidK[Eff[E, *]]): Eff[E, A] = G.foldK(ps)
+
+  def amb[E, A, F[_]](using
       F: Alternative[F]
   ): Eff[NonDet :* E, A] => Eff[E, F[A]] =
     Eff.handlerRet(
@@ -49,3 +55,8 @@ object NonDet:
       ,
       _
     )
+
+  def allResults[E, A]: Eff[NonDet :* E, A] => Eff[E, List[A]] = amb[E, A, List]
+
+  def firstResult[E, A]: Eff[NonDet :* E, A] => Eff[E, Option[A]] =
+    amb[E, A, Option]
diff --git a/examples/src/main/scala/Example.scala b/examples/src/main/scala/Example.scala
index a921375..e618c4d 100644
--- a/examples/src/main/scala/Example.scala
+++ b/examples/src/main/scala/Example.scala
@@ -124,7 +124,7 @@ object Example:
         y <- NonDet.choose
       yield (x && !y) || (!x && y)
 
-    println(NonDet.allResults[Nothing, Boolean, Vector](xor).run)
+    println(NonDet.allResults(xor).run)
 
     def branches[F[_]: Monad](using
         F: MonoidK[F],
@@ -135,9 +135,9 @@ object Example:
         y <- G.foldK(List(4, 5, 6).map(_.pure[F]))
       yield (x, y)
 
-    println(branches[Vector])
+    println(branches[List])
 
-    println(NonDet.allResults[Nothing, (Int, Int), Vector](branches).run)
+    println(NonDet.allResults(branches).run)
 
     // def logging[F[_]: Monad](implicit F: Tell[F, Log]): F[Unit] =
     //  // Example of some logging activity in your application
@@ -180,7 +180,7 @@ object Example:
 
     println(
       NonDet
-        .allResults[Nothing, (Int, String), Option](
+        .firstResult(
           Parse.parse("999")(Parse.digit)
         )
         .run
@@ -191,7 +191,7 @@ object Example:
 
     println(
       NonDet
-        .allResults[Nothing, (Int, String), Option](
+        .firstResult(
           Parse.parse("[12345678]")(
             brackets(Parse.number)
           )
@@ -201,9 +201,9 @@ object Example:
 
     println(
       NonDet
-        .allResults[Nothing, (String, String), Option](
+        .firstResult(
           Parse.parse("bazz")(
-            Parse.choice(
+            NonDet.choice(
               Parse.string("foo") :: Parse
                 .string("bar") :: Parse.string("baz") :: Nil
             )
diff --git a/examples/src/main/scala/Parse.scala b/examples/src/main/scala/Parse.scala
index db73c8d..c23e6ff 100644
--- a/examples/src/main/scala/Parse.scala
+++ b/examples/src/main/scala/Parse.scala
@@ -4,10 +4,10 @@ import evidence.*
 import evidence.effect.*
 import cats.implicits._
 import evidence.effect.NonDet.given
-import cats.Alternative
 import cats.Monad
 import cats.MonoidK
 import cats.Foldable
+import cats.Alternative
 
 type Parse = [E, Ans] =>> Parse.Syn[E, Ans]
 
@@ -24,7 +24,7 @@ object Parse:
     )(p)
 
   def many[E, A](p: Eff[E, A]): NonDet :? E ?=> Eff[E, List[A]] =
-    Alternative[Eff[E, *]].combineK(many1(p), List.empty[A].pure)
+    Alternative[Eff[E, *]].combineK(many1(p), Nil.pure)
 
   def many1[E, A](p: Eff[E, A]): NonDet :? E ?=> Eff[E, List[A]] =
     for
@@ -32,10 +32,6 @@ object Parse:
       xs <- many(p)
     yield x :: xs
 
-  def choice[F[_]: Monad, G[_], A](
-      ps: G[F[A]]
-  )(using F: MonoidK[F], G: Foldable[G]): F[A] = G.foldK(ps)
-
   def parse[E, A](
       input: String
   ): NonDet :? E ?=> Eff[Parse :* E, A] => Eff[E, (A, String)] =