72 lines
2.4 KiB
C++
72 lines
2.4 KiB
C++
/* @file List.hpp
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*
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* author: Roland Conybeare, Aug 2025
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*/
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#pragma once
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#include "Sequence.hpp"
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namespace xo {
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namespace obj {
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/** @class List
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* @brief A list element -- aka cons cell
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**/
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class List : public Sequence {
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public:
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/** the empty list. unique sentinel object **/
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static gp<List> nil;
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/** @return non-null iff @p x is actually a List cell (or nil) **/
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static gp<List> from(gp<Object> x);
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/** @return list with first element @p car, and tail @p cdr **/
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static gp<List> cons(gp<Object> car, gp<List> cdr);
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/** @return list with single element @p x1 **/
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template <typename T>
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static gp<List> list(T && x1) {
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return List::cons(x1, nil);
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}
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/** @return list with elements @p x1, ..., @p rest in argument order **/
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template <typename T, typename... Rest>
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static gp<List> list(T && x1, Rest &&... rest) {
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return List::cons(x1, list(rest...));
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}
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/** @return true iff list is empty **/
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bool is_nil() const { return this == nil.ptr(); }
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gp<Object> head() const { return head_; }
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gp<List> rest() const { return rest_; }
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/** @return first element in list; synonym for @ref head **/
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gp<Object> car() const { return head_; }
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/** @return remainder of list after first element; synonym for @ref rest **/
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gp<Object> cdr() const { return rest_; }
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/** @return number of top-level elements in this list **/
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std::size_t size() const;
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gp<Object> list_ref(std::size_t i) const;
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void assign_head(gp<Object> head);
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void assign_rest(gp<List> rest);
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// inherited from Object..
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virtual TaggedPtr self_tp() const final override;
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virtual void display(std::ostream & os) const final override;
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virtual std::size_t _shallow_size() const final override;
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virtual Object * _shallow_copy() const final override;
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virtual std::size_t _forward_children() final override;
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private:
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List(gp<Object> head, gp<List> rest);
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private:
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gp<Object> head_;
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gp<List> rest_;
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};
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}
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} /*namespace xo*/
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