newlispfanclub.alh.net

Posted: **Sat Sep 23, 2006 11:13 pm**

The examples given for the use of (let are leaving me confused. I think I understand what (let is for, but in the context of the example, isn't it unnecessary?

Code: Select all

    (define (sum-sq a b)
      (let ((x (* a a)) (y (* b b)))
        (+ x y)))

    (sum-sq 3 4)  → 25

    (define (sum-sq a b)            ; alternative syntax
        (let (x (* a a) y (* b b))
            (+ x y)))

Wouldn't this make more sense in defining a sum-of-squares routine?

Code: Select all

(define (sum-sq a b)
          (+ (* a a) (* b b)))

I know it doesn't demonstrate the use of (let, but (let seems unnecesssary: I checked, and a and b don't seem to be affected outside this function. So what's the point of using (let to isolate values here? Or is it just an artificial example and I shouldn't worry so much? ;-)

Posted: **Sat Sep 23, 2006 11:22 pm**

Wouldn't this make more sense in defining a sum-of-squares routine?

Yes, absolutely, the example has been kept simple for didactic purposes.

Lutz

Posted: **Sun Sep 24, 2006 7:46 pm**

Lutz wrote:
Wouldn't this make more sense in defining a sum-of-squares routine?
Yes, absolutely, the example has been kept simple for didactic purposes.

Lutz

Thanks, just making sure I wasn't missing something.

gc

Posted: **Sun Oct 08, 2006 10:19 pm**

The point is to localise x and y, not a and b.
e.g. suppose x and y were created with set rather than let:

Code: Select all

(define (sum-sq a b)
    (set 'x (* a a))
    (set 'y (* b b))
    (+ x y))

(println (sum-sq 3 4))
(println x)
(println y)

In this case x and y continue to exist outside of the scope they were created in (whereas they would not in the let version).

newlispfanclub.alh.net

Puzzled by (let examples in the documentation

Puzzled by (let examples in the documentation