The Scheme Programming Language History and Significance Dmitry Nesvizhsky CIS24 Professor Danny Kopec

Scheme: History Started as an experiment in programming language design by challenging some fundamental design assumptions A dialect of the LISP Programming Language invented by Guy Lewis Steele Jr. and Gerald Jay Sussman

Scheme: History Emerged from MIT in the mid-1970's Originally called Schemer Shortened to Scheme because of a 6 character limitation on file names Designed to have very few regular constructs which compose well to support a variety of programming styles Functional, object-oriented, and imperative

Significant Language Features Supports lexical scoping, uniform evaluation rules, and uniform treatment of data types Does not support the concept of a pointer, uninitialized variables, specialized looping constructs, or explicit storage management All data type are equal What one can do to one data type, one can do to all data types

Significant Language Features There are seven kinds of expressions Constant Variable reference Procedure creation Procedure application Conditional Assignment Sequence

Significant Language Features Scheme also has the usual assortment of data types Characters Strings Arrays Lists Numbers Functions (also called procedures) Boolean Ports Symbols

Significant Language Features Numbers are especially interesting An integer is a rational and a real is a complex Scheme requires no looping constructs Any function which calls itself in the "tail" position is just a loop

Significant Language Features Scheme has several important advantages It is elegantly simple in that regular structure and trivial syntax avoids "special case" confusion Its expressiveness means that one spends little time trying to work around the language It lets users concentrate on what they want to say rather than on how to say it

Significant Language Features Scheme has several important advantages (continued) Supports a variety of styles (including object-oriented) Allows users to better match their solution style to the style of the problems to be solved Its formal underpinnings make reasoning about programs much easier

Significant Language Features Scheme has several important advantages (continued) Its abstractive power makes it easy to separate system specific optimizations from reusable code Its compos ability makes it easy to construct systems from well-tested components

Areas of Application Scheme is currently gaining favor as a first programming language in universities and is used in industry by such companies as TI, HP, and Sun

Areas of Application Here are a few statistics regarding the schools using Scheme: schools using Scheme 286 colleges/universities worldwide of these use Scheme in introductory courses 159 colleges/universities USA only - 49 of these use Scheme in introductory courses 73 secondary schools worldwide 64 secondary schools USA only

Sample Program 1 This program prints the phrase "Hello World“ ; (Scott Ruthfield) (define hello-world (lambda () (begin (write ‘Hello-World) (newline) (hello-world))))

Sample Program 2 Scheme is an imperative language that favors recursion over iteration The basic data structure is the list In Scheme, "car" returns the first element of a list and "cdr" returns the remaining elements of the list There is no need for an "iterator class" or pointers, as in C++ In this program cdr recursion is used as an iterator, moving from element to element in the list The result from each recursive call becomes the input, or term, for the addition operator, there by eliminating the need for a temporary sum variable

Sample Program 2 (continued) ; List Sum ; This program was found in "An Introduction to ; Scheme" by Jerry Smith, Prentice Hall, 1988 (define (list-sum lst) (cond ((null? lst) 0) ((pair? (car lst)) (+(list-sum (car lst)) (list-sum (cdr lst)))) (else (+ (car lst) (list-sum (cdr lst))))))

Scheme Performance Table