Function read 

pub(crate) fn read<'a, 'd>(
    swaption: El<'a, 'd>,
    ctx: &Context<'_>,
) -> Result<Read<'a, 'd>, FpmlError>

Reads a swaption: a European or Bermudan swaption on its swap, its premium as a fee, a straddle as a payer and a receiver.