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I hope this comment is still relevant, as I joined the discussion rather late. It intersects somewhat with the discussions on space retention and stream-unfoldn. The reference implementation of stream-partition appears to evaluate the entire stream before returning any results. As such, it has no advantages over a function that operates on lists. ;; Obvious quick fix: This tests each element twice, ;; and it may have problems with space retention. (define (stream-partition pred? strm) (values (stream-filter pred? strm) (stream-filter (lambda (x) (not (pred? x))) strm))) It might be possible to write a stream-partition that was incremental but still tested each element only once. However, I think it would require explicit shared state between the two result streams. __________________________________________________ Do you Yahoo!? Yahoo! Web Hosting - establish your business online http://webhosting.yahoo.com