Implement FunctorFilter and add some more laws (#108)

* Add mapOrFail, and some more laws

* Use FunctorFilter and names for Parsers

core/shared/src/main/scala/cats/parse/Parser.scala

@@ -21,7 +21,7 @@
 
 package cats.parse
 
-import cats.{Eval, Monad, Defer, Alternative, FlatMap, Now, MonoidK, Order}
+import cats.{Eval, FunctorFilter, Monad, Defer, Alternative, FlatMap, Now, MonoidK, Order}
 import cats.data.{AndThen, Chain, NonEmptyList}
 
 import cats.implicits._
@@ -189,6 +189,33 @@ sealed abstract class Parser[+A] {
   def map[B](fn: A => B): Parser[B] =
     Parser.map(this)(fn)
 
+  /** Transform parsed values using the given function, or fail on None
+    *
+    * When the function return None, this parser fails
+    * This is implemented with select, which makes it more efficient
+    * than using flatMap
+    */
+  def mapFilter[B](fn: A => Option[B]): Parser[B] = {
+    val leftUnit = Left(())
+
+    val first = map { a =>
+      fn(a) match {
+        case Some(b) => Right(b)
+        case None => leftUnit
+      }
+    }
+    Parser.select(first)(Parser.Fail)
+  }
+
+  /** Transform parsed values using the given function, or fail when not defined
+    *
+    * When the function is not defined, this parser fails
+    * This is implemented with select, which makes it more efficient
+    * than using flatMap
+    */
+  def collect[B](fn: PartialFunction[A, B]): Parser[B] =
+    mapFilter(fn.lift)
+
   /** If the predicate is not true, fail
     * you may want .filter(fn).backtrack so if the filter fn
     * fails you can fall through in an oneOf or orElse
@@ -357,11 +384,30 @@ sealed abstract class Parser1[+A] extends Parser[A] {
   def <*[B](that: Parser[B]): Parser1[A] =
     (this ~ that.void).map(_._1)
 
+  /** This method overrides `Parser#collect` to refine the return type.
+    */
+  override def collect[B](fn: PartialFunction[A, B]): Parser1[B] =
+    mapFilter(fn.lift)
+
   /** This method overrides `Parser#map` to refine the return type.
     */
   override def map[B](fn: A => B): Parser1[B] =
     Parser.map1(this)(fn)
 
+  /** This method overrides `Parser#mapFilter` to refine the return type.
+    */
+  override def mapFilter[B](fn: A => Option[B]): Parser1[B] = {
+    val leftUnit = Left(())
+
+    val first = map { a =>
+      fn(a) match {
+        case Some(b) => Right(b)
+        case None => leftUnit
+      }
+    }
+    Parser.select1(first)(Parser.Fail)
+  }
+
   /** This method overrides `Parser#flatMap` to refine the return type.
     */
   override def flatMap[B](fn: A => Parser[B]): Parser1[B] =
@@ -1279,16 +1325,28 @@ object Parser extends ParserInstances {
       case (notSingleChar, _) => notSingleChar.map(Impl.ConstFn(b))
     }
 
-  implicit val catsInstancesParser1: FlatMap[Parser1] with Defer[Parser1] with MonoidK[Parser1] =
-    new FlatMap[Parser1] with Defer[Parser1] with MonoidK[Parser1] {
+  implicit val catsInstancesParser1
+      : FlatMap[Parser1] with Defer[Parser1] with MonoidK[Parser1] with FunctorFilter[Parser1] =
+    new FlatMap[Parser1] with Defer[Parser1] with MonoidK[Parser1] with FunctorFilter[Parser1] {
       def empty[A] = Fail
 
       def defer[A](pa: => Parser1[A]): Parser1[A] =
         defer1(pa)
 
+      def functor = this
+
       def map[A, B](fa: Parser1[A])(fn: A => B): Parser1[B] =
         map1(fa)(fn)
 
+      def mapFilter[A, B](fa: Parser1[A])(f: A => Option[B]): Parser1[B] =
+        fa.mapFilter(f)
+
+      override def filter[A](fa: Parser1[A])(fn: A => Boolean): Parser1[A] =
+        fa.filter(fn)
+
+      override def filterNot[A](fa: Parser1[A])(fn: A => Boolean): Parser1[A] =
+        fa.filter { a => !fn(a) }
+
       def flatMap[A, B](fa: Parser1[A])(fn: A => Parser1[B]): Parser1[B] =
         flatMap10(fa)(fn)
 
@@ -2175,16 +2233,28 @@ object Parser extends ParserInstances {
 }
 
 abstract class ParserInstances {
-  implicit val catInstancesParser: Monad[Parser] with Alternative[Parser] with Defer[Parser] =
-    new Monad[Parser] with Alternative[Parser] with Defer[Parser] {
+  implicit val catInstancesParser
+      : Monad[Parser] with Alternative[Parser] with Defer[Parser] with FunctorFilter[Parser] =
+    new Monad[Parser] with Alternative[Parser] with Defer[Parser] with FunctorFilter[Parser] {
       def pure[A](a: A): Parser[A] = Parser.pure(a)
 
       def defer[A](a: => Parser[A]) = Parser.defer(a)
 
       def empty[A]: Parser[A] = Parser.Fail
 
+      def functor = this
+
       override def map[A, B](fa: Parser[A])(fn: A => B): Parser[B] = Parser.map(fa)(fn)
 
+      def mapFilter[A, B](fa: Parser[A])(f: A => Option[B]): Parser[B] =
+        fa.mapFilter(f)
+
+      override def filter[A](fa: Parser[A])(fn: A => Boolean): Parser[A] =
+        fa.filter(fn)
+
+      override def filterNot[A](fa: Parser[A])(fn: A => Boolean): Parser[A] =
+        fa.filter { a => !fn(a) }
+
       override def product[A, B](fa: Parser[A], fb: Parser[B]): Parser[(A, B)] =
         Parser.product(fa, fb)
 

core/shared/src/test/scala/cats/parse/ParserTest.scala

@@ -496,10 +496,29 @@ object ParserGen {
     )
   }
 
+  def genParser[A](genA: Gen[A]): Gen[Parser[A]] =
+    for {
+      genT <- gen
+      fn <- Gen.function1(genA)(genT.cogen)
+    } yield genT.fa.map(fn)
+
+  def genParser1[A](genA: Gen[A]): Gen[Parser1[A]] =
+    for {
+      genT <- gen1
+      fn <- Gen.function1(genA)(genT.cogen)
+    } yield genT.fa.map(fn)
+
+  implicit def arbParser[A: Arbitrary]: Arbitrary[Parser[A]] =
+    Arbitrary(genParser(Arbitrary.arbitrary[A]))
+
+  implicit def arbParser1[A: Arbitrary]: Arbitrary[Parser1[A]] =
+    Arbitrary(genParser1(Arbitrary.arbitrary[A]))
 }
 
 class ParserTest extends munit.ScalaCheckSuite {
 
+  import ParserGen.{arbParser, arbParser1}
+
   val tests: Int = if (BitSetUtil.isScalaJs) 50 else 2000
 
   override def scalaCheckTestParameters =
@@ -1517,6 +1536,20 @@ class ParserTest extends munit.ScalaCheckSuite {
     }
   }
 
+  property("a.backtrack.peek.orElse(b.peek) == (a.backtrack.orElse(b)).peek") {
+    forAll(ParserGen.gen, ParserGen.gen, Arbitrary.arbitrary[String]) { (a, b, str) =>
+      val pa = a.fa.backtrack
+      val pb = b.fa
+
+      val left = pa.peek.orElse(pb.peek)
+      val right = pa.orElse(pb).peek
+
+      val leftRes = left.parse(str).toOption
+      val rightRes = right.parse(str).toOption
+      assertEquals(leftRes, rightRes)
+    }
+  }
+
   property("a.peek == a.peek *> a.peek") {
     forAll(ParserGen.gen, Arbitrary.arbitrary[String]) { (a, str) =>
       val pa = a.fa.peek
@@ -1580,6 +1613,28 @@ class ParserTest extends munit.ScalaCheckSuite {
     }
   }
 
+  property("!fail == unit") {
+    forAll { (str: String) =>
+      val left = !Parser.fail
+      val right = Parser.unit
+
+      val leftRes = left.parse(str)
+      val rightRes = right.parse(str)
+      assertEquals(leftRes, rightRes)
+    }
+  }
+
+  property("!pure(_) == fail") {
+    forAll { (str: String, i: Int) =>
+      val left = !Parser.pure(i)
+      val right = Parser.fail
+
+      val leftRes = left.parse(str).toOption
+      val rightRes = right.parse(str).toOption
+      assertEquals(leftRes, rightRes)
+    }
+  }
+
   property("anyChar.repAs[String] parses the whole string") {
     forAll { (str: String) =>
       assertEquals(Parser.anyChar.repAs[String].parse(str), Right(("", str)))
@@ -1615,24 +1670,36 @@ class ParserTest extends munit.ScalaCheckSuite {
     }
   }
 
-  /*
   property("select(pa.map(Left(_)))(pf) == (pa, pf).mapN((a, fn) => fn(a))") {
-    forAll(ParserGen.gen, ParserGen.gen, Arbitrary.arbitrary[String]) { (genP, genRes, str) =>
-      val pa = genP.fa
-      val pf = null: Parser[genP.A => genRes.A]
-      assertEquals(Parser.select(pa.map(Left(_)))(pf).parse(str), pf.ap(pa).parse(str))
+    forAll { (pa: Parser[Int], pf: Parser[Int => String], str: String) =>
+      assertEquals(
+        Parser.select(pa.map(Left(_)))(pf).parse(str),
+        (pa, pf).mapN((a, f) => f(a)).parse(str)
+      )
+    }
+  }
+
+  property("select1(pa.map(Left(_)))(pf) == (pa, pf).mapN((a, fn) => fn(a))") {
+    forAll { (pa: Parser1[Int], pf: Parser[Int => String], str: String) =>
+      assertEquals(
+        Parser.select(pa.map(Left(_)))(pf).parse(str),
+        (pa, pf).mapN((a, f) => f(a)).parse(str)
+      )
     }
   }
-   */
 
   property("select(pa.map(Right(_)))(pf) == pa") {
-    forAll(ParserGen.gen, ParserGen.gen, Arbitrary.arbitrary[String]) { (genP, genRes, str) =>
-      val pa = genRes.fa
-      val pf: Parser[genP.A => genRes.A] = Parser.fail
+    forAll { (pa: Parser[String], pf: Parser[Int => String], str: String) =>
       assertEquals(Parser.select(pa.map(Right(_)))(pf).parse(str), pa.parse(str))
     }
   }
 
+  property("select1(pa.map(Right(_)))(pf) == pa") {
+    forAll { (pa: Parser1[String], pf: Parser[Int => String], str: String) =>
+      assertEquals(Parser.select1(pa.map(Right(_)))(pf).parse(str), pa.parse(str))
+    }
+  }
+
   property("p.filter(_ => true) == p") {
     forAll(ParserGen.gen, Arbitrary.arbitrary[String]) { (genP, str) =>
       val res0 = genP.fa.filter(_ => true).parse(str)
@@ -1671,4 +1738,44 @@ class ParserTest extends munit.ScalaCheckSuite {
       )
     }
   }
+
+  property("mapFilter is the same as filter + map") {
+    forAll { (pa: Parser[Int], fn: Int => Option[String], str: String) =>
+      val left = pa.mapFilter(fn)
+      val right = pa.map(fn).filter(_.isDefined).map(_.get)
+
+      assertEquals(left.parse(str), right.parse(str))
+    }
+  }
+
+  property("mapFilter is the same as filter + map Parser1") {
+    forAll { (pa: Parser1[Int], fn: Int => Option[String], str: String) =>
+      val left = pa.mapFilter(fn)
+      val right = pa.map(fn).filter(_.isDefined).map(_.get)
+
+      assertEquals(left.parse(str), right.parse(str))
+    }
+  }
+
+  property("collect is the same as filter + map") {
+    forAll { (pa: Parser[Int], fn: Int => Option[String], str: String) =>
+      val left = pa.collect {
+        case i if fn(i).isDefined => fn(i).get
+      }
+      val right = pa.map(fn).filter(_.isDefined).map(_.get)
+
+      assertEquals(left.parse(str), right.parse(str))
+    }
+  }
+
+  property("collect is the same as filter + map Parser1") {
+    forAll { (pa: Parser1[Int], fn: Int => Option[String], str: String) =>
+      val left = pa.collect {
+        case i if fn(i).isDefined => fn(i).get
+      }
+      val right = pa.map(fn).filter(_.isDefined).map(_.get)
+
+      assertEquals(left.parse(str), right.parse(str))
+    }
+  }
 }