Is .2 irrational?

[Paul Smee]

There was a 'language' (focal, I believe it was, and was a bit similar to
early BASIC) on the PDP-9 (never saw it anywhere else, was standard there,
yes Virginia I am that old) which stored all numbers as fractions -- that
is, each number used 2 storage locations, one for the numerator and one
for the denominator.  So, subject to storage-unit length, any rational
number within range could be represented exactly.

There were some obvious difficulties, of course, such as the fact that the
maximum magnitude which could be represented depended on the denominator
of the fraction.  Still, it offers an approach...