One more comment.  I really think the SRFI will be much more useful
if you specify a "getenv" procedure, with the following prototype:

(getenv variable [default-value])

Variable must be a string naming an environment variable.  The result
is the value of the environment variable as a string.  If the variable
does not exist then the default-value is returned if specified,
otherwise it is an error (an exception is raised or an error is
signaled).

A "putenv" procedure is much less interesting for SRFI 22.  It is only
if you have the ability to spawn sub-processes that it becomes useful,
and that's probably best left to another SRFI.

Marc