immutable SymbolTable

object SymbolTable {
  val empty = new SymbolTable(Map.empty[String, Symbol] :: Nil)
}

final class SymbolTable private(scopes: List[Map[String, Symbol]]) {
  def inCurrentScope(name: String): Boolean = scopes.head.contains(name)

  def resolve(name: String): Option[Symbol] = scopes.view.map(_.get(name)).find(!_.isEmpty).flatten

  def inScope(name: String): Boolean = !resolve(name).isEmpty

  def isTypeAlias(name: String): Boolean = resolve(name).exists(_.isInstanceOf[TypeAlias])

  def add(name: String, symbol: Symbol): SymbolTable = new SymbolTable(scopes.head + (name -> symbol) :: scopes.tail)

  def openScope: SymbolTable = new SymbolTable(Map.empty[String, Symbol] :: scopes)

  def closeScope: SymbolTable = new SymbolTable(scopes.tail)

  override def toString = scopes.toString
}