Function interp_hashset_add 

fn interp_hashset_add(
    args: &[RValue],
    named: &[(String, RValue)],
    context: &BuiltinContext<'_>,
) -> Result<RValue, RError>

Add a string element to a HashSet.

@param s integer scalar: hashset ID @param value character scalar: the element to add @return logical scalar: TRUE if the element was new, FALSE if already present