How to append the current list with another element in Scheme?

Let's say I have a list: a b a a a c e. I want to get rid of all adjacent duplicate, i.e. the two a's in the middle. So the list becomes a b a c e.

The algorithm that I current h开发者_开发百科ave in mind is,

- Check if the current value is equal to the next value by

(equal? (car lst) (car (cdr lst)))

If they are equal then I want to skip the duplicate element, but I don't know how to achieve this behavior in Scheme? Any idea?

- If they're not equal, keep traversing through the list.

By the way, is there a way to implement iterative for loop in Scheme for these types of problem? Because I feel recursion is just overkill for this simple problem.

Thanks,

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I have not written Scheme for a long time, but maybe this will be helpful to you:

(define (remove-adjacent-duplicates list)
    (if (empty? list)                    
        '()                              
        (if (equal? (car list) (cadr list))
            (remove-adjacent-duplicates (cdr list))
            (cons (car list) (remove-adjacent-duplicates (cdr list)))))

Oh, and don't be afraid of recursion, especially in Scheme. It's fun! :)

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Here's an iterative answer for this problem using fold:

(define (uniq lst)
  (fold (lambda (elem result)
          (if (and (pair? result) (equal? elem (car result)))
              result
              (cons elem result)))
        '() (reverse lst)))

(In future, any time you're trying to convert a list to something, consider using fold, and any time you're trying to convert something to a list, consider using unfold. They're very powerful functions!)

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In this case you would want to save the car of the cdr to cons onto the result of your recursive call (ditch the car, it makes checking in a case with like 3 a's easier). Now the question you are asking is what is the recursive call on. Well, now you cons the car of the cdr onto the recurion on the cdr.