Modification of the integral procedure

The integral procedure used above was analogous to the ''implicit'' definition of the infinite stream of integers in section 3.5.2. Alternatively, we can give a definition of integral that is more like integers-starting-from (also in section 3.5.2):

(define (integral integrand initial-value dt)
  (cons-stream initial-value
               (if (stream-null? integrand)
                   the-empty-stream
                   (integral (stream-cdr integrand)
                             (+ (* dt (stream-car integrand))
                                initial-value)
                             dt))))

When used in systems with loops, this procedure has the same problem as does our original version of integral . Modify the procedure so that it expects the integrand as a delayed argument and hence can be used in the solve procedure shown above.

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