CODEWITHSUNDEEP
scheme
DJPlayer
DJPlayer

Reputation: 3294

storing values in Scheme globally

I have a series of mathmetical operations I need to perform. The input of the function is n.

the first two operations are summations. using n. The result needs stored as a variable to be used in later functions.

ex. 

main func(n)
       func1 (n)
         returns a1

       func2 (n)
         returns b1

       func4 
         uses b1 to compute c1

       etc....

I've created all the functions sepearted but need to use a main function that merely takes in n, and a way to store the variables globally for use in later functions (without changing them). these are the first 2 functions. 

(define (main n)
 (define (a1func n)
   (let* ((a1 0))
   (let* ((i (- n 1)))
        (if (= n 1) 0
      (+(/ 1 i) (a1func(- n 1)))))))

 (define (a2func n)
   (let ((a2 0))
   (let ((i (- n 1)))
   (if (= n 1) 0
        (+(/ 1 (expt i 2)) (a2func(- n 1)))))))

  (define b1 
    (if (= n 1) 0
        (/(+ n 1)(* 3(- n 1))))) 
  (define b2 
    (if (= n 1) 0
        (/(* 2 (+ n 3 (expt n 2))) (*(- n 1)(* 9 n)))))
  (define c1 (- b1 (/ 1 a1)))   
  (define c2 (+ (- b2 (/ (+ n 2) (* a1 n))) (/ a2 (expt a1 2))))
  (define e1 (/ c1 a1))
  (define e2 (/ c2 (+ (expt a1 2) a2)))
  (list e1 e2))

Upvotes: 3

Views: 1910

Answers (2)

knivil
knivil

Reputation: 906

Functional programming is different from imperative programming. Scheme is a functional language. Do not use bound variables as memory locations. But if you need something like memory locations then use vector.

If you want to use the value of variable in another functior then pass it to that function as a parameter:

(define (fun1 n) ...)
(define (fun2 n) ...)
(define (fun4 n b) ...)

(define (main n)
  (let ((a1 (fun1 n))
        (b1 (fun2 n)))
    (let ((c1 (fun4 n b1)))
      ( .....)))...))))

Upvotes: 1

Vijay Mathew
Vijay Mathew

Reputation: 27174

The idiomatic way to make a function compute result using the output of another function is composition. In the following example, you want add2 to work on the result of add1 and achieve that by composing the functions:

> (define (add1 n) (+ 1 n))
> (define (add2 n) (+ 2 n))

> (add2 (add1 10))
=> 13

If you really want to work with global state, you can do that with the help of closures so that the global namespace itself is not spoiled:

(define (make-adder n)
  (lambda (msg)
    (case msg
      ((one) 
       (set! n (+ 1 n)))       
      ((two) 
       (set! n (+ 2 n))))
    n))


> (define adder (make-adder 10))
> (adder 'one)
11
> (adder 'two)
13

Upvotes: 0

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