Just a couple of comments on the fix:
1) The stream-low-level-lazy, ...strict, ...delay and ...force
implementations have a pretty serious bug. This bug was discovered by
Alexandro Forero Cuervo and discussed on the SRFI-45
list (with some spillover to the SRFI-40 list). I posted a
fix - please see the patched SRFI-45 document for the details.
(also, AFC posted a patched version of SRFI-40 incorporating
a version of the fix to this list).
2) I believe the discussion of stream-unfoldn in the first
part of the implementation section was obsoleted by the
SRFI-45-style promises (indeed, the actual implementation
below it was then changed back to using the naive
version, which should be correct and safe for space).