I have made what I hope are final changes to the SRFI-1 list library.
There are three sets of changes:

- I've added CONCATENATE and CONCATENATE!.
  (concatenate lists) = (apply append lists)
  The problem with the APPLY/APPEND idiom is that you can blow out
  many Scheme implementations if you apply an n-ary function to too many
  arguments. This has been a problem in Scheme 48, for example. CONCATENATE
  doesn't have this problem.

- I've made UNFOLD be the name of the function that generates list elements
  left-to-right, and UNFOLD-RIGHT be the name of the function that generates
  list elements right-to-left. This is in keeping with the general use of
  the FOO and FOO-RIGHT convention.

  I originally had these backwards. Note that left fold & right unfold are
  inverses, as are right fold and left unfold (which is what led me astray).
  It's important to get this straight now, to establish a convention for
  other unfolders on other composite data structures (e.g., strings & vectors).

- I've added some functions from the Haskell list library:
    split-at  lis i -> [list, list]
    split-at! lis i -> [list, list]

    take-while  pred lis -> list
    take-while! pred lis -> list
    drop-while  pred lis -> list

    span   pred lis -> [list list]
    span!  pred lis -> [list list]
    break  pred lis -> [list list]
    break! pred lis -> [list list]

I apologise for making more additions and changes to the library; it is
way past time to put this thing to bed.

These changes have been incorporated into the draft spec & source found at
    ftp://ftp.ai.mit.edu/people/shivers/srfi/srfi-1/srfi-1.html
    ftp://ftp.ai.mit.edu/people/shivers/srfi/srfi-1/srfi-1.txt
    ftp://ftp.ai.mit.edu/people/shivers/srfi/srfi-1/srfi-1-reference.scm
I have polished these documents to a ready-to-go-final state. Note that
the html spec has an "active" procedure index, with internal links to
all the procedure definitions, so you can easily jump to the definitions
of the new procedures if you wish to check them out.

Today is Sunday. If I hear no complaints by Friday, SRFI-1 will be moved
to "final."
    -Olin