[plt-scheme] for in-range (was redefinition in module)

On Mar  1, Jos Koot wrote:
> Hi
> I had a look in scheme/private/for.ss. If I understand the code
> correctly in-range computes subsequent values of the variable by
> accumulated addition of the step to the start. When some decades ago
> do-loops with real variables were introduced in fortran, there was
> discussion about how to approach it:
> 
> 1: accumulated addition of the step to the start.
> 
> 2: compute the number of iterations in advance as
>    n=(inexact->exact (ceiling (/ (- finish start) step))))
>    and loop (for ((var (in-range 0 n 1))) (let ((var (+ start (* i step)))) etc))
> 
> The second method was choosen, because it was argued that
> accumulative addition also would accumulate error. The code below
> illustrates the difference:

This is a *much* smaller problem in Scheme, since for the relatively
rare cases that you don't want to loop on just integers, you can just
use exact rationals.

-- 
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                  http://www.barzilay.org/                 Maze is Life!