Question

How can I implement loop in plt-scheme like in java-

for(int i=0;i<10;){
     for(int j=0;j<3;){
          System.out.println(""+j);
          j++;
     }
      System.out.println(""+i);
      i++;
}

Answer 1

Your example in Java doesn’t directly map onto the Scheme language by just learning a few new keywords as there aren’t explicit constructs for implementing a for loop in Scheme (unless you write a construct yourself!). The cookbook way to do this in Scheme is to define a recursive function that loops over a list. Here’s an example of how to do a for-loop style function in Scheme:

(define (doit x x-max dx)
  (if (<= x x-max)
    (begin
      ;;...perform loop body with x...
      (doit (+ x dx) x-max dx))))

(doit a b dx) ; execute loop from a to b in steps of dx

Taken from this page:

Guile and Scheme Links

Here’s another link to a page that describes the ideas you need to understand to translate loops from imperative languages to Scheme:

Scheme Looping Constructs

Scheme is a really interesting language to learn, you should also read the Structure and Interpretation of Computer Programs, which is the textbook formerly used for teaching Scheme at MIT.