A Lisp-Like Linked List ClassJeffrey D. Oldham2000 Jan 15Andrew Koenig presents a Lisp-like linked list C++ class in chapter 15 of Ruminations on C++. Thisis a short introduction to using the class (header file and implementation file).1 The Linked List ClassUnlike some programming languages, the C++ programming language requires explicit type declarations.Thus, in the following, I will refer to lists of ints, but lists of any other type can also be created.A list iseither an empty listor an item followed by a list.1.1 Empty ListsTo create an empty list, useSeq<int>()To check if a list L is empty, useL.empty()which returns the boolean value true if the list has no items and otherwise false. Using L in a place wherea boolean is expected yields true if the list is not empty and otherwise false. For example, if (L) cout<< "list is not emptyn";.1.2 Nonempty ListsTo add an integer, e.g., 3, to the an existing list L, useSeq<int>(3,L)To check if a list is nonempty, negate the result of checking for an empty list.To obtain a list L’s first item, which has int type, useL.hd()To obtain the rest of the list, which has Seq<int> type, useL.tl() c2000 Jeffrey D. Oldham ([email protected]). All rights reserved. This document may not be redistributedin any form without the express permission of the author.11.3 ExampleThe subst function substitutes one string for another string in a linked list of strings.#include "seq.h" // Note the "", not <>, causes this// directory to be searched as well as the// standard places implied by <>.#include <string>// Given a list of strings, return a (new) list with one string// substituted for the other string.Seq<string> subst(const string & oldString, const string & newString,const Seq<string> & SL) {if (SL.empty())return SL;else if (!SL.empty()) {if (SL.hd() == oldString)return Seq<string>(newString, subst(oldString, newString, SL.tl()));elsereturn Seq<string>(SL.hd(), subst(oldString, newString, SL.tl()));}}2 Logistics of Using the CodeTo use the linked list class with a program you wrote, copy the two files (header file and implementationfile) to the directory containing the program’s C++ code. One way to do this is to use the “Save As...”item on a WWW browser’s file menu.Another way is to issue the shell command wget http://www.cs.trinity.edu/˜joldham/-1321/lectures/lists/seq.h http://www.cs.trinity.edu/˜joldham/1321/lectures/-lists/seq.cc. The wget program copies the specified WWW links to your local directory. See alsothe wget manual. Isn’t wget slick?In your C++ program, add the line#include "seq.h"near the other header inclusions. See also this sample
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