CODEWITHSUNDEEP
schemegimpscript-fu
noway
noway

Reputation: 2585

Nested while loop in Scheme with Gimp?

I'm writing a Gimp Script-Fu script, and trying to use a nested while loop. x is set to 15, y is set to 30. y loops up to 35, yet x stays at 15 and the loop quits. What is wrong here? Why is the value of x not changed?

(while (< x 20)
  (while (< y 35)    
    (gimp-message (string-append (number->string x) "-" (number->string y)))
    (set! y (+ y 1)))
  (set! x (+ x 1)))

Upvotes: 1

Views: 985

Answers (1)

Jason Sperske
Jason Sperske

Reputation: 30436

y is never being reset back to 0. Your code will increment y up to 35, then increment x 20 times, however on each subsequent increment of x y is still set to 35.

If you wanted to go over each combination of values of x and y then you would need code more like this:

(while (< x 20)
    (set! y 0)
    (while (< y 35)    
            (gimp-message (string-append (number->string x) "-" (number->string y)))
             (set! y (+ y 1))
            )
    (set! x (+ x 1))
)

Here is a more complete example now that I've had time to work through this question with Gimp (I'm using print instead of gimp-message because I'm working in the console, but it should be interchangeable). To start I'm defining a function called SO that accepts the arguments, x, y that both represents pairs of min and max values:

(define (SO x y)
  (let* ((x! (car x)) (y! (car y)))
    (while (< x! (car (cdr x)))
      (set! y! (car y))
      (while (< y! (car (cdr y)))
        (print (string-append (number->string x!) "-" (number->string y!)))
        (set! y! (+ y! 1))
      )
      (set! x! (+ x! 1))
    )
  )
)

Inside this function, I'm pulling out the first and last values of x and y (with (car x) and (car (cdr x)) then I'm using let* to create two inner variables calledx!andy!that I will be altering the value of (to remove side effects of havingxandy` change after the function is called). If you call this function like so:

(SO '(15 20) '(30 35))

You get the following output:

"15-30"
"15-31"
"15-32"
"15-33"
"15-34"
"16-30"
"16-31"
"16-32"
"16-33"
"16-34"
"17-30"
"17-31"
"17-32"
"17-33"
"17-34"
"18-30"
"18-31"
"18-32"
"18-33"
"18-34"
"19-30"
"19-31"
"19-32"
"19-33"
"19-34"

Upvotes: 2

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