Scheme.kt

package ekko.tree

/**
 * Type schemes are used to describe qualified types.
 * Each TGen that appears in [qual] represents a generic that the kind is given
 * by `[kinds] !! n`.
 */
data class Scheme(val kinds: List<Kind>, val qual: Qual<Typ>) {
  companion object {
    fun forall(vararg args: Kind) = fun(qual: Qual<Typ>): Scheme {
      return Scheme(args.toList(), qual)
    }
  }

  override fun toString(): String = when {
    kinds.isEmpty() -> qual.toString()
    else -> {
      val kinds = kinds.mapIndexed { index, kind ->
        "('${letters.elementAt(index)} : $kind)"
      }

      "forall $kinds. $qual"
    }
  }
}