Simple memoization extension with capacity == 1.

Memoize.kt

package io.charlag.memoize

fun <A, E> ((A) -> E).memoize(): ((A) -> E) {
  var arg: A? = null
  var result: E? = null

  return { a ->
    if (a != arg) {
      arg = a
      result = this(a)
    }
    result!!
  }
}

fun <A, B, E> ((A, B) -> E).memoize(): ((A, B) -> E) {
  var arg: Pair<A,B>? = null
  var result: E? = null

  return { a, b ->
    if (a != arg?.first || b != arg?.second) {
      arg = a to b
      result = this(a, b)
    }
    result!!
  }
}