38 lines
821 B
Kotlin
38 lines
821 B
Kotlin
package com.smallhacker.util
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interface ImmStack<E>: Iterable<E> {
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fun isEmpty(): Boolean
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val top: E?
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fun pop(): ImmStack<E>
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fun push(value: E): ImmStack<E> = ImmStackImpl(this, value)
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}
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fun <T> immStack(): ImmStack<T> {
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@Suppress("UNCHECKED_CAST")
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return EmptyImmStack as ImmStack<T>
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}
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private class ImmStackImpl<E>(private val parent: ImmStack<E>, override val top: E):
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ImmStack<E> {
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override fun isEmpty() = false
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override fun pop(): ImmStack<E> = parent
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override fun iterator(): Iterator<E> {
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return sequenceOf(top).plus(parent).iterator()
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}
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}
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private object EmptyImmStack: ImmStack<Any?> {
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override fun isEmpty() = true
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override val top: Any? = null
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override fun pop() = this
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override fun iterator() = emptySequence<Any?>().iterator()
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} |