Exercise 3.77: The integral procedure
used above was analogous to the “implicit” definition of the infinite stream
of integers in 3.5.2.  Alternatively, we can give a definition of
integral that is more like integers-starting-from (also in
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.