converting decimal numbers into rational in scheme functions

[Janek Warchoł]

Hi,

i have a function that takes a moment as the argument:

foo =
#(define-music-function (parser location mom)
   (ly:moment?)
   #{
     \override Score.SpacingSpanner.base-shortest-duration = #mom
   #})

\new Staff {
  \foo #(ly:make-moment 1 50)
  c'4 d' e' f'
}

Now, i would like to be able to supply a decimal number and have it
converted to a rational number (i.e. a fraction, which can be easily
converted to a moment), so that i could call the function like this

\foo #0.02  % 1/50 = 0.02

Is there any smart way to do this (a built-in function?  I've searched
for one but haven't found any), or do i have to write a
decimal->rational converter?  Would anyone want to help with this?

best,
Janek