This does kinda exist in Scheme and Racket:

    > (/ 1 10)
    1/10
    > (exact? (/ 1 10))
    1/10
    > (/ 1.0 10.0)
    0.1
    > (exact? (/ 1.0 10.0))
    #f
    > (/ #e1.0 #e10.0)   ; #e for "exact"
    1/10
    > (/ #i1 #i10)       ; #i for "inexact"
    0.1

As mentioned in HN before [1], Pyret (which has the same origin as Racket) went further and made the exact literal (now "Exactnum") default, so the inexact literal (now "Roughnum") always requires a preceding `~`.

[1] https://news.ycombinator.com/item?id=28263486

This does not make sense: floating point numbers are not really "approximate". For example, small integer arithmetic using floats is guaranteed to be exact. Your language would be very confusing for this common use case.