Function zet::do_calculation

pub fn do_calculation(
    operation: OpName, 
    first_operand: &[u8], 
    rest: impl IntoIterator<Item = Result<Vec<u8>, Error>>, 
    output: impl FnOnce(Box<dyn Iterator<Item = &'_ [u8]> + '_>) -> Result<(), Error>
) -> Result<(), Error>

Calculates and prints the set operation named by op. Each file in files is treated as a set of lines:

• OpName::Union prints the lines that occur in any file,
• OpName::Intersect prints the lines that occur in all files,
• OpName::Diff prints the lines that occur in the first file and no other,
• OpName::Single prints the lines that occur in exactly one file, and
• OpName::Multiple prints the lines that occur in more than one file.