6.001 Recitation #2 – Feb 7, 2003

RI: Konrad Tollmar,

http://www.ai..mit.edu/~konrad/6001/

The MIT Scheme programming environment

Basic Scheme

- primitives / combinations

- abstractions

- lambda

- special form cond / if

1. Evaluate these expressions

(+ 2 3)

(+ (* (/ 12 2) 1000) 1)

(+ 4)

(- 3)

(/ 5)

(/ 60 5 2 3)

(+)

(*)

(-)

(define a 1)

(define a+1 (+ a 1))

a

a+1

(define a 2)

a+1

(define four 4)

four

(+ four 1)

(+ (four) 1)

2. Lambda / Special forms

A. Evaluate these lambda procedures

(define six (lambda () 6))

six

(+ six 1)

(+ (six) 1)

B. Define the lambda procedures twice and second.

(define twice (…))

(twice 2) ==> 4
(twice 3) ==> 6

(define second … )

(second 2 15 3) ==> 15
(second 34 -5 16) ==> -5

C. What is difference?

(define plus +)

(define add

(lambda (x y) (+ x y)))

D. Define an abs function

(define abs …)

E. Procedure abstractions

Define two procedures average and square. Use these procedures to crate a procedure avaragesquares that (surprise;-) average squares, e.g.

(avaragesquares 4 2)

è 10

F. Procedure abstractions

Define a procedure that converts US Dollars to Swedish kronor.

(define RATE 0.105)

(convert “USD” 10)

è 95 SEK

(convert “SEK” 100)

è 10.5 SEK

Hint:

(string=? "PIE" "PIE") => #t

Create some nicer output:

(convert "USD" 10)

USD->SEK: 95.23809523809524

;Value: 95.23809523809524

Hint:

string-append string ...

number->string number

display “string”