Format options for Interval or Duration?

[chexxor]

MomentJS has a way to turn a duration into a human-readable string:

https://momentjs.com/docs/#/durations/humanize/

moment.duration(1, "minutes").humanize(); // a minute
moment.duration(2, "minutes").humanize(); // 2 minutes
moment.duration(24, "hours").humanize();  // a day

I've found myself wanting to turn an IsoDuration into a string. I'm not sure if that would belong in this library or not, as it seems tricky to specify the output format, as I haven't seen a similar specification like date's "YYYY". I imagine one way to implement this is like:

formatDuration :: { biggestFirst :: Boolean, ... } -> Duration -> String

-- It might be better to move the unit conversion into a separate function.
msFromDuration :: Duration -> Milliseconds
formatMS :: { fitToBiggestUnit :: Boolean, forceToUnit :: DurationComponent } -> Milliseconds -> String

-- I imagine would need a way to customize this for a locale.
newtype FormatDurationLocale :: FormatDurationLocale (DurationComponent -> String)
formatMS :: FormatDurationLocale -> FormatDurationOpts -> Milliseconds -> String

-- Test it out
-- > formatMS englishDurationLocale defaultDurationOpts { fitToBiggest = true } (msFromDuration tenMinutes)
-- 10 minutes

-- > formatMS (^ same as that ^) (msFromDuration tenDaysTenMinutes)
-- 1 week, 3 days, 10 minutes

-- > formatMS (englishDurationLocale defaultDurationOpts { forceToUnit = Week }) (msFromDuration tenDaysTenMinutes)
-- 1.31 weeks

Have you guys thought about this? Looks like current formatting is only to-from the ISO-8601 duration format.