t3x.org / sketchy / library / negate.html
SketchyLISP
Reference
  Copyright (C) 2006
Nils M Holm

negate

Conformance: SketchyLISP Core

Purpose: Compute the negative value of a number.

Arguments:
X - number

Implementation:

(define (negate x)
  (letrec
    ((_negate (lambda (x)
      (cond ((eq? (car x) '-) (cdr x))
        ((eq? (car x) '+) (cons '- (cdr x)))
        (#t (cons '- x))))))
    (list->integer
      (_negate (integer->list x)) #t)))

Example:

(negate 125) 
=> -125

See also:
digits, -, negative?.