show.hs

showRational :: Int64 -> Rational -> Builder
showRational len n = sign <> TS.showb d <> "." <> decs
  where
    sign =
      if num < 0
        then "-"
        else mempty
    decs = fromLazyText . TL.take len . toLazyText $ go next
    (d, next) = abs num `quotRem` den
    go 0 = mempty
    go x =
      let (d', next') = (10 * x) `quotRem` den
       in TS.showb d' <> go next'
    num = numerator n
    den = denominator n