Comment 4 for bug 181601

> The output of the do macro (all macros) gets re-expanded until it's fully in core form.

Ok, this is not the the case it seems, as letrec is passed to eval-core, and hence wont be expanded further by the expander.

Example:
(do ((x 0 (+ x 1)))
     ((> x 10))
    (display 12))

What is passed to eval-core:
(letrec ((g$loop$226
           (case-lambda
             ((g$x$228)
              (if (> g$x$228 '10)
                (if '#f '#f (void))
                (begin (display '12) (g$loop$226 (+ g$x$228 '1))))))))
  (g$loop$226 '0))

Now eval-core will use the implementation based letrec, and not the one from psyntax.