The trouble with R[45]RS is that there's so little you can rely on having available, though portable SRFIs of course help. 

John Cowan          http://vrici.lojban.org/~cowan        xxxxxx@ccil.org
"Your honour puts yourself to much trouble correcting my English and
doubtless the final letter will be much better literature; but it will
go from me Mukherji to him Bannerji, and he Bannerji will understand it a
great deal better as I Mukherji write it than as your honour corrects it."
        --19th-century Indian civil servant to his British superior