(*sigh*) So just rewrite it with DO [which is IMHO uglier
than the LOOP version, but YM obviously V]:

    > (with-open-file (s "x^2.txt")
        (do ((line (read-line s nil nil) (read-line s nil nil))
             (results nil (cons (split-sequence:split-sequence #\tab line)
                                results)))
            ((null line) (reverse results))))

    (("0" "0") ("0.010101" "0.00010203") ("0.020202" "0.000408122")
     ("0.030303" "0.000918274"))
    >

Or, if you prefer an imperative, side-effecting style
[generates pretty much the same code]:

      (with-open-file (s "x^2.txt")
        (do ((line (read-line s nil nil) (read-line s nil nil))
             (results nil))
            ((null line) (reverse results))
          (push (split-sequence:split-sequence #\tab line) results)))

+---------------
| "csv-parser" - got that working well on CSV files - but big "proper"
| (!) program to do much more complicated job.  Could have hacked it to
| do tab-delimited -- but started afresh.
+---------------

I didn't see that request in the thread, or I would have posted this
[of course, it uses that ugly LOOP thingy]:

    ;;; PARSE-CSV-LINE -- Parse one CSV line into a list of fields,
    ;;; stripping quotes and field-internal escape characters.
    ;;; Lexical states: '(normal quoted escaped quoted+escaped)
    ;;;
    (defun parse-csv-line (line)
      (when (or (string= line "")           ; special-case blank lines
                (char= #\# (char line 0)))  ; or those starting with "#"
        (return-from parse-csv-line '()))
      (loop for c across line
            with state = 'normal
            and results = '()
            and chars = '() do
        (ecase state
          ((normal)
           (case c
             ((#\") (setq state 'quoted))
             ((#\\) (setq state 'escaped))
             ((#\,)
              (push (coerce (nreverse chars) 'string) results)
              (setq chars '()))
             (t (push c chars))))
          ((quoted)
           (case c
             ((#\") (setq state 'normal))
             ((#\\) (setq state 'quoted+escaped))
             (t (push c chars))))
          ((escaped) (push c chars) (setq state 'normal))
          ((quoted+escaped) (push c chars) (setq state 'quoted)))
        finally
         (progn
           (push (coerce (nreverse chars) 'string) results) ; close open field
           (return (nreverse results)))))

-Rob