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schemeracketvariable-assignmentredefinition

How to fix the 'cannot change constant' error

I have this code so far 

(define (max f g) 
  (define (int-max x y)
    (if (> x y) x y))
  (lambda (x) (int-max (f x) (g x))))

it gives me the error define-values: assignment disallowed; cannot change constant constant: max

I'm not sure how to fix this or what it means.

Solution

  • The problem you are facing is that max is already defined and you are trying to re-define it.

    More importantly, name max is not appropriate for what you are trying to use it for. You are calling max with couple of arguments that are functions. It returns a lambda that can be invoked with a variable.

    Your envisioning usage such as

    ((max sin cos) 10)

    A name such as max-proc-value would be more appropriate and will avoid the problem that you have run into.