Above example is just what i want.but it has some restricts:
it can process 1 recursive digit such as .3333..., but cannot process 2 or more recursive digit (maybe 6 is enough). for example: 0.142857142857...->1/7 ,0.076923076923...->1/13, which has 6 recursive digit. It also need skip leading digit that may not be recursive, e.g. 0.4777?->43/90 ,that leading 4 is not recursive.
Maybe more work needed ,it's not a simple task anyway .
Yann's "DecimalToFraction" is really very useful for me . maybe it could be put plugin to enhance maths function.
Thanks a lot.