Variable Definitions

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Variable Definitions

When you are defining only functions, the order of definitions does not matter. However, the order for variable definitions is significant, because DrScheme evaluates the right-hand side immediately, without looking at the remaining definitions. Therefore,

(define RADIUS 5)
(define DIAMETER (* 2 RADIUS))

is fine, but

(define DIAMETER (* 2 RADIUS))
(define RADIUS 5)

produces the error ``reference to undefined identifier: RADIUS''. DrScheme does not yet know the definition of RADIUS when it tries to evaluate (* 2 RADIUS).

PLT