tpolecat

scala> case class Bad(a: Int) { override def equals(a:Any) = true }
scala> val f = (n:Int) => Bad(n)
scala> val g = (b:Bad) => b.a

...

scala> Set(1,2,3).map(f andThen g)
res2: scala.collection.immutable.Set[Int] = Set(1, 2, 3)

scala> Set(1,2,3).map(f).map(g)

tpolecat

// Where the hell does B come from? Looks like a type variable is escaping.

scala> Left(1).disjunction
res14: scalaz.\/[Int,B] = -\/(1)

// It's not Nothing

scala> Left(1).disjunction : (Int \/ Nothing)
<console>:17: error: type mismatch;
 found   : scalaz.\/[Int,B]

tpolecat

name := "just-scalaz"

version := "0.1"

scalaVersion := "2.10.2"

libraryDependencies ++= Seq(
  "org.scalaz" % "scalaz-core_2.10" % "7.0.3",
  "org.scalaz" % "scalaz-effect_2.10" % "7.0.3"
)

tpolecat

// Scala widens Char to Int here, rather than unifying to AnyVal

scala> List('a', 1)
res7: List[Int] = List(97, 1)

// And even widens to Double. Nutty

scala> List('a', 3.14)
res14: List[Double] = List(97.0, 3.14)

tpolecat

// Eta-expansion turns A* to Seq[A]

scala> def foo(ns:Int*) = ns.sum
foo: (ns: Int*)Int

scala> foo(1,2,3)
res0: Int = 6

scala> val foov = foo _
foov: Seq[Int] => Int = <function1>

tpolecat

class Animal(val name: String) {
  override def equals(a: Any): Boolean =
    a match {
      case a: Animal if a.name == name => true
      case _ => false
    }
} 

class Cat(name: String, val color: String) extends Animal(name) {
  override def equals(a: Any): Boolean =

tpolecat

// rank 1

type num[a] = (a => a) => a => a

def zero[a]: num[a] = f => x => x
def succ[a](n: num[a]): num[a] = f => x => f(n(f)(x))

def eval(n: num[Int]): Int = n(_ + 1)(0)

// rank 2

tpolecat

def exists[A](as: List[A], f: A => Boolean): Boolean = 
  as match {
    case Nil      => false
    case a :: as0 => if (f(a)) true else exists(as0, f)
  }

def forall[A](as: List[A], f: A => Boolean): Boolean =
  !exists(as, (a: A) => !f(a))

tpolecat

scala> def a: Any = List(1,2,3).map(x => x + 1)
a: Any

scala> def b: Any = List(1,2,3).map(x => return x + 1)
b: Any

scala> a
res1: Any = List(2, 3, 4)

scala> b

tpolecat

scala> def foo[A[_]] = 1
foo: [A[_]]=> Int

scala> foo[List]
res11: Int = 1

scala> foo[Int]
<console>:24: error: Int takes no type parameters, expected: one
              foo[Int]
                  ^