a fraction calculator's interface without over.key

1.22: adde/math/handling fractions:
. the Kochan`Fractions Calculator has an over.key,
for allowing a fraction to be entered without eval'ing it;
another way to handle this
is to enter complex expressions:
nothing is eval'd until you hit enter,
so, expecting fractions, the only division happens when
there is the form a/b / c/d .
. also, the policy could be that
div's would be eval'd only when
they represent exact fractions:
eg, 2/5 is 2/5, while 1/2 is 0.5 [1.31:
that does present a problem with the base being decimal, 2*5
but the storage's base being binary?
you could have an exact fraction like 1/5 = 0.2 in base 10,
but that is a irrational number in base 2 .]
. even if it did eval each operator a.s.a.p.,
it could simply reduce and stay exact:
14/10 = 7/5 = (1+2/5).