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Editorial Team
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Asked: 2026-05-30T05:35:25+00:00

(define (even-odd x) (if ( ==(% x 2 ) 0) (1) (0))) when i

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(define (even-odd x)
(if ( ==(% x 2 ) 0) (1) (0)))

when i call( even-odd 5 )
i get this message

;Unbound variable: %
;To continue, call RESTART with an option number:
; (RESTART 11) => Specify a value to use instead of %.
; (RESTART 10) => Define % to a given value.
; (RESTART 9) => Return to read-eval-print level 9.
; (RESTART 8) => Return to read-eval-print level 8.
; (RESTART 7) => Return to read-eval-print level 7.
; (RESTART 6) => Return to read-eval-print level 6.
; (RESTART 5) => Return to read-eval-print level 5.
; (RESTART 4) => Return to read-eval-print level 4.
; (RESTART 3) => Return to read-eval-print level 3.
; (RESTART 2) => Return to read-eval-print level 2.
; (RESTART 1) => Return to read-eval-print level 1.

;Start debugger? (y or n):

Am i doing something wrong ?Also let me know how to select text in edwin.

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1 Answer

  1. Editorial Team

    You have a few problems here; namely that you’re mistaken in the names of the procedures you’re trying to call.

    • % should be modulo
    • == should be eqv?
    • As zvrba noted, remove parenthesis surrounding 0 and 1

    or, if you’re simply trying to tell whether a number is even or odd, a simpler and cleaner way to do this is to simply use the builtin even?.

    (even? 5)
> #f

    or if you actually want 0 and 1 as a result, a cleaner expression could be 

    (if (even? x) 1 0)
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