While Ikarus provides `directory-list', it doesn't expose the more primitive {open,read,close}dir() API directly. As a consequence, there will be problems with large directories, where unnecessary allocation is forced upon the user even if she would just filter a few items out of the directory, or just do something to all the files in the directory (imagine implementing "rm -rf" in Scheme).
Below I've pasted the description of a possible API, taken from "The Nearly Complete Scheme48 1.3 Reference Manual" [0]:
— procedure: open-directory-stream filename –> dir-stream
— procedure: directory-stream? object –> boolean
— procedure: read-directory-stream dir-stream –> filename or #f
— procedure: close-directory-stream dir-stream –> unspecified
Directory streams are the low-level interface provided by POSIX to enumerate the contents of a directory. Open-directory-stream opens a new directory stream that will enumerate all of the files within the directory named by filename. Directory-stream? is the disjoint type predicate for directory streams. Read-directory-stream consumes the next filename from dir-stream and returns it, or returns #f if the stream has finished. Note that read-directory-stream will return only simple filenames, not full pathnames. Close-directory-stream closes dir-stream, removing any storage it required in the operating system. Closing an already closed directory stream has no effect.
[0] http://mumble.net/~campbell/darcs/s48-refman/
Will add soon.