A Lisp-Like Linked List Class¹

2000 Jan 15

Andrew Koenig presents a Lisp-like linked list C++ class in chapter 15 of Ruminations on C++. This is a short introduction to using the class (header file and implementation file).

The Linked List Class

Unlike 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 is

either an empty list
or an item followed by a list.

Empty Lists

To create an empty list, use

Seq<int>()

To check if a list L is empty, use

L.empty()

which returns the boolean value true if the list has no items and otherwise false. Using L in a place where a boolean is expected yields true if the list is not empty and otherwise false. For example, if (L) cout << "list is not empty n";.

Nonempty Lists

To add an integer, e.g., 3, to the an existing list L, use

Seq<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, use

L.hd()

To obtain the rest of the list, which has Seq<int> type, use

L.tl()

Example

The subst function substitutes one string for another string in a linked list of strings.

Logistics of Using the Code

To use the linked list class with a program you wrote, copy the two files (header file and implementation file) 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/~joldham0/1321/lectures/lists/seq.h http://www.cs.trinity.edu/~joldham0/1321/lectures/lists/seq.cc. The wget program copies the specified WWW links to your local directory. See also the 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 program.

Footnotes

2000-01-18