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Filter Input Deleting Duplicate Lines

 #!/usr/local/bin/scsh \
 -o tables -e main -s


 USAGE: delete-duplicate-lines.scm < INPUT > OUTPUT
 Copy std INPUT to std OUTPUT w/o duplicates of lines
 !#


 ;; Copy the lines of stdin to stdout
 ;; adding raunch and excitement.
 (define (delete-duplicate-lines)
   (let ((previous-lines (make-string-table)))
     (awk (read-line) (line) ()
          ((table-ref previous-lines line))
          (else (table-set! previous-lines line #t)
                (display line)
                (newline)))))


 (define (main args)
   (if (= (length args) 1)
       (delete-duplicate-lines)
       (format #t "Usage: ~a < INPUT > OUTPUT~%" (first args))))

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