Function interp_op_mul 

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

Multiplication operator as a function.

@param e1 first operand @param e2 second operand @return product of e1 and e2