37 lines
984 B
Scala
37 lines
984 B
Scala
package green.thisfieldwas.embracingnondeterminism.extractables.seq
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sealed trait List[+A] extends Extractable[A] {
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def head: A
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def tail: List[A]
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def ::[B >: A](x: B): List[B] = new ::(x, this)
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// satisfies non-empty Seq if present
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// but Seq can be empty by definition, so you have to blindly trust that it
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// has at least one element as this doesn't free you from Seq's void effect
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def extract: Seq[A] = {
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def go(list: List[A]): Seq[A] = list match {
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case h :: t => h +: go(t)
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case Nil => Seq.empty
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}
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Seq(head) ++ go(tail)
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}
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// satisfies true if present
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// satisfies false if void
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// does not indicate if more instances after head
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def isExtractable: Boolean = this.isInstanceOf[::[A]]
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}
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case class ::[+A](head: A, tail: List[A]) extends List[A]
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case object Nil extends List[Nothing] {
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def head: Nothing = throw new NoSuchElementException("Nil.head")
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def tail: Nothing = throw new NoSuchElementException("Nil.tail")
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}
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