// parses a token
token := "every 3 secs from 06:30 to 08:30"
ret := ParseSched(v.token, func(bytime *SchedRecurByTime, byday *SchedRecurByDay) {
    // do something
})

// RecurByTime = every decimal_digit (hrs|mins|secs)  ["from" time "to" time] .
// RecurByDay = (every|ordinal) Days ["of" (Months)] (time) .

// VALID input examples
// "every 21 hrs"
// "every 3 secs from 06:30 to 08:30"
// "every 05 mins from 06:30 to 09:30"
// "every monday 05:30"
// "every mon 05:30"
// "every wed 15:40"
// "every sat 05:10"
// "every tue of january 17:23"
// "1st thu of sept 17:23"
// "321st sat of dec 17:23"
// "343rd sun of oct 17:23"
// "313th sun of feb 17:23"
// "312th sun of feb 17:23"
// "232nd sun 17:23"
// "232nd mon,sun 17:23"
// "312th sun of feb,jan,mar 17:23"
//
// INVALID input examples:
// "every tuesday 25:30"
// "every friday 24:70"
// "0th thu of sept 17:23"
// "11st thu of january 17:23"
// "211st thu of january 17:23"
// "321rd sat of dec 17:23"
// "313rd sun of oct 17:23"

type SchedRecurByTime struct {
    N         int
    ClockLbl  string
    FromClock string
    ToClock   string
}

type SchedRecurByDay struct {
    Ord int

    // value is just an empty struct = struct{}{}
    Days map[string]struct{}

    // value is just an empty struct = struct{}{}
    Months map[string]struct{}

    Clock string
}