hoggla.scala

sealed trait Type {}
case class BuiltinType(t: String) extends Type {
  override def toString = t
}
case class UnknownType(name: String) extends Type {
  override def toString = name
}
case class FunctionType(from: Type, to: Type) extends Type {
  override def toString: String = {
    val fromS = from.toString
    (if (fromS.contains("->")) s"($fromS)" else fromS) + " -> " + to
  }
}
case class HKT1(name: String, subtype: Type) extends Type {
  override def toString: String = {
    val subtypeS = subtype.toString
    name + " " + (if (subtypeS.contains("->")) s"($subtypeS)" else subtypeS)
  }
}
val Boolean = BuiltinType("Boolean")
val Int = BuiltinType("Int")

def matches(t1: Type, t2: Type): Boolean = (t1, t2) match {
  case (UnknownType(_), _) => true
  case (_, UnknownType(_)) => true
  case (HKT1(_, a), HKT1(_, b)) => matches(a, b)
  case (BuiltinType(a), BuiltinType(b)) => a == b
  case (FunctionType(fromA, toA), FunctionType(fromB, toB)) => matches(fromA, fromB) && matches(toA, toB)
  case _ => false
}

val signatures: Seq[FunctionType] = Seq(
//  FunctionType(Boolean, Int),
//  FunctionType(Int, Boolean),
//  FunctionType(UnknownType("a"), UnknownType("b")),
//  FunctionType(UnknownType("a"), Int),
//  FunctionType(HKT1("m", UnknownType("a")), Int),
//  FunctionType(FunctionType(UnknownType("a"), UnknownType("b")), FunctionType(UnknownType("a"), FunctionType(Int, Int))),
  FunctionType(HKT1("m", UnknownType("a")), FunctionType(FunctionType(UnknownType("a"), HKT1("m", UnknownType("b"))), HKT1("m", UnknownType("a")))),
  FunctionType(HKT1("m", UnknownType("a")), FunctionType(HKT1("m", UnknownType("b")), HKT1("m", UnknownType("a"))))
)
println("Defined functions:")
signatures.foreach(s => println(" - " + s))
def printMatches(lookingFor: Type): Unit = {
  val matching = signatures.filter(matches(lookingFor, _))
  println(s"${matching.length} matching for $lookingFor:")
  matching.foreach(s => println(" - " + s))
}
printMatches(FunctionType(UnknownType("a"), UnknownType("b")))
printMatches(FunctionType(UnknownType("a"), UnknownType("m b")))