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139 lines
3.5 KiB
C++
139 lines
3.5 KiB
C++
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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#ifndef EXECUTABLE_SEMANTICS_INTERPRETER_STACK_H_
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#define EXECUTABLE_SEMANTICS_INTERPRETER_STACK_H_
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#include <cassert>
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#include <cstddef>
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#include <iterator>
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#include "executable_semantics/interpreter/list_node.h"
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namespace Carbon {
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// A persistent stack data structure.
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//
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// - Note: this data structure leaks memory.
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template <class T>
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struct Stack {
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// A forward iterator over elements of a `Stack`.
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struct Iterator {
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using value_type = T;
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using difference_type = std::ptrdiff_t;
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using pointer = const T*;
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using reference = const T&;
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using iterator_category = std::forward_iterator_tag;
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Iterator(ListNode<T>* x) : p(x) {}
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Iterator(const Iterator& mit) : p(mit.p) {}
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Iterator& operator++() {
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p = p->next;
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return *this;
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}
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Iterator operator++(int) {
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Iterator tmp(*this);
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operator++();
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return tmp;
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}
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bool operator==(const Iterator& rhs) const { return p == rhs.p; }
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bool operator!=(const Iterator& rhs) const { return p != rhs.p; }
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const T& operator*() { return p->curr; }
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const T* operator->() { return &p->curr; }
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private:
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ListNode<T>* p;
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};
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// The position of the first/`Top()` element, or `end()` if
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// `this->IsEmpty()`.
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auto begin() const -> Iterator { return Iterator(head); }
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// The position one past that of the last element.
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auto end() const -> Iterator { return Iterator(nullptr); }
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// Creates an empty instance.
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Stack() { head = nullptr; }
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// Creates an instance containing just `x`.
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Stack(T x) : Stack() { Push(x); }
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// Pushes `x` onto the top of the stack.
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void Push(T x) { head = new ListNode<T>(x, head); }
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// Returns a copy of `*this`, with `x` pushed onto the top.
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auto Pushing(T x) const -> Stack {
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auto r = *this;
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r.Push(x);
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return r;
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}
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// Removes and returns the top element of the stack.
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//
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// - Requires: !this->IsEmpty()
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auto Pop() -> T {
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assert(!IsEmpty() && "Can't pop from empty stack.");
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auto r = head->curr;
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head = head->next;
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return r;
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}
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// Removes the top `n` elements of the stack.
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//
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// - Requires: n >= 0 && n <= Count()
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void Pop(int n) {
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assert(n >= 0 && "Negative pop count disallowed.");
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while (n--) {
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assert(head != nullptr && "Can only pop as many elements as stack has.");
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head = head->next;
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}
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}
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// Returns a copy of `*this`, sans the top element.
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//
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// - Requires: !this->IsEmpty()
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auto Popped() const -> Stack {
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auto r = *this;
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r.Pop();
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return r;
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}
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// Returns the top element of the stack.
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//
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// - Requires: !this->IsEmpty()
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auto Top() const -> T {
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assert(!IsEmpty() && "Empty stack has no Top().");
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return head->curr;
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}
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// Returns `true` iff `Count() > 0`.
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auto IsEmpty() const -> bool { return head == nullptr; }
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// Returns `true` iff `Count() > n`.
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//
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// - Complexity: O(`n`)
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auto CountExceeds(int n) const -> bool {
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if (n < 0)
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return true;
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for (auto p = head; p != nullptr; p = p->next) {
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if (n-- == 0)
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return true;
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}
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return false;
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}
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// Returns the number of elements in `*this`.
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auto Count() const -> int { return std::distance(begin(), end()); }
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private:
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// A linked list of cells containing the elements of self.
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ListNode<T>* head;
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};
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} // namespace Carbon
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#endif // EXECUTABLE_SEMANTICS_INTERPRETER_CONS_LIST_H_
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