CODEWITHSUNDEEP
functional-programmingscheme
abhi09
abhi09

Reputation: 81

which programming practice to follow to evaluate expression in scheme

I am solving problems from htdp.org. I would like to know in scheme which is a better practice to evaluate long expressions having a common operator like '+' or '*'.

Example :

> (* 1 10 10 2 4)                 ; Version A
> (* 1 (* 10 (* 10 (* 2 4))))     ; Version B

Should I follow A or B. Also I please consider the above example for algebraic expressions like surface area of cylinder.

-Abhi

Upvotes: 2

Views: 179

Answers (2)

law-of-fives
law-of-fives

Reputation: 643

A bit of a followup on this. (* a b c ...) is not necessarily equivalent to (* (* a b) ...) when you're talking about timing.

Some implementations may recognize the common operation, but try timing these two definitions of factorial:

(define (f1 n)
  (let loop ((up 2)
             (down n)
             (a 1))
    (cond ((> up down) a)
          ((= up down) (* a up))
          (else
           (loop (+ 1 up) (- 1 down)
                 (* a up down))))))

(define (f2 n)
  (let loop ((up 2)
             (down n)
             (a 1))
    (cond ((> up down) a)
          ((= up down) (* a up))
          (else
           (loop (+ 1 up) (- 1 down)
                 (* a (* up down)))))))

The second procedure is considerably faster than the first for me.

Upvotes: 1

Shaun
Shaun

Reputation: 4018

The real question should be, do they produce different results? Let's try in our REPL:

>> (* 1 10 10 2 4)
800
>> (* 1 (* 10 (* 10 (* 2 4))))
800
>>

Since they're essentially the same (using your example), I'd opt for going with lower ceremony / noise in the code. Use the first one.

Upvotes: 7

Related Questions