how get all sundays in between given 2 dates?

If you are looking to find the number of Sundays between two dates -

1. Create a rule called TEST_addNumberToDate with following code

ri!date + ri!number

2. Then create another rule -

with(
  local!count: tointeger(ri!endDate - ri!startDate),
  local!totalDatesInRange: apply(rule!TEST_addNumberToDate(ri!startDate,_),enumerate(local!count)+1),
  local!dayOfTheWeek: apply(fn!weekday,local!totalDatesInRange),
  count(wherecontains(1,dayOfTheWeek))
)

If you are looking to find the number of non working days between two dates, try below code -

with(
 local!int_totalNumberOfDays: tointeger(ri!endDate - ri!startDate),
 local!int_totalNumberOfWorkingDays: calworkdays(ri!startDate,ri!endDate),
 local!int_totalNumberOfNonWorkingDays: local!int_totalNumberOfDays - local!int_totalNumberOfWorkingDays,
 local!int_totalNumberOfNonWorkingDays
)