`eval_str'
----------

eval_str(STR)
     :: STR ($BJ8;zNs(B) $B$rI>2A$9$k(B.

RETURN
     $B%*%V%8%'%/%H(B

STR
     Asir $B$N(B parser $B$,<uM}2DG=$JJ8;zNs(B

   * Asir $B$N(B parser $B$,<uM}2DG=$JJ8;zNs$rI>2A$7$F$=$N7k2L$rJV$9(B.

   * $BI>2A2DG=$JJ8;zNs$O(B, $B<0$rI=$9$b$N$K8B$k(B.

   * $BO@M}E*$K$O(B `rtostr()' $B$N5U4X?t$H$J$k(B.

     [0] eval_str("1+2");
     3
     [1] fctr(eval_str(rtostr((x+y)^10)));
     [[1,1],[x+y,10]]

$B;2>H(B
     *Note `rtostr': rtostr

