Scheme is currently gaining favor as a first programming language in universities and is used in industry by such companies as DEC, TI, Tektronix, HP, and Sun. Scheme is a general-purpose computer programming language.

It is a high-level language(OOP), supporting operations on structured data such as strings, lists, and vectors, as well as operations on more traditional data such as numbers and characters.

Getting Started

Download Latest PLT Scheme Version This program will install like any other program in few clicks.

Running DrScheme & DrScheme Interface

After its install, It can be launched form the Start Menu or from the shortcut icon on the desktop.

Dr Scheme Interface is very simple, above part is the Definition window & just below it you can see the Interaction window.

Getting into Programming

According to Ken Dickey, Scheme is a small, exceptionally clean language which is, very importantly, fun to use. The language was designed to have very few, regular constructs which compose well to support a variety of programming styles including functional, object-oriented, and imperative.

The language standard is only about 50 pages, including a formal, denotational definition of its semantics. Scheme is prefix and C is infix:

In Scheme                                      In C

	(+ 2 3 4)			(2 + 3 + 4)

	(< low x high)			((low < x) && (x < high))

	(+ (* 2 3) (* 4 5))		((2 * 3) + (4 * 5))

	(f x y)				f(x, y)

        (define (sq x) (* x x))		int sq(int x) { return (x * x) }

In Scheme, unnamed functions are created with the key word lambda.

(lambda (x) (* x x))    	-> a function

(define sq (lambda (x) (* x x))

(sq 9)				-> 27

((lambda (x) (* x x)) 9)	-> 27

((if (foo? x) * +) 2 3 4)	-> if (foo? x) is true,

						 then (* 2 3 4)

						 else (+ 2 3 4)

(define (curried-add x) (lambda (y) (+ x y))

(define add3 (curried-add 3)) ;; add3 is a funciton

(add3 7)		-> 10

((curried-add 3) 7)	-> 10

There are seven kinds of expressions:

  Constant:			'foo #Z 3 "a string"

  Variable reference:	foo joe a-long-name-for-an-identifier +

  Procedure creation:	(lambda (z) (* z z z))

  Procedure application:	(cube 37)

  Conditional:			(if (< x 3) sqrt modulo)

  Assignment:			(set! x 5)

  Sequence:			(begin (write x) (write y) (newline))

Scheme has the usual assortment of data types:

  Characters: #a #A #b #B #space #newline

  Strings: "A little string"

  Arrays (called vectors): #(1 2 "string" #x 5)

  Lists: (a little (list of) (lists))

  Numbers: 47 1/3 2.3 4.3e14 1+3i

  Functions (also called procedures)

  Booleans: #t #f

  Ports (e.g. open files)

  Symbols: this-is-a-symbol foo a32 c$23*4&7+3-is-a-symbol-too!

- A vector’s contents can be any data objects.

- Symbols may include the characters + - . * / < = > ! ? : $ % _ & ~ and ^.

- Symbols are case insensitive.

- Symbols are used for identifiers, so identifiers (variable names) are case insensitive.

Useful Resources for Learning Scheme Online

1. R. Kent Dybvig. “The Scheme Programming Language, Second Edition” View

2. Chez Scheme User’s Guide View

3. PLT Scheme Guide by Matthew Flatt, Robert Bruce Findler View

4. Teach Yourself Scheme in Fixnum Days by Dorai Sitaram View

I think that those who want to start programming in Scheme, they can start with it more easily now. The resources that have been mentioned above are itself more then sufficient to learn Scheme.

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