Function interp_op_sub 

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

Subtraction operator as a function (unary negation or binary subtraction).

@param e1 first operand (or sole operand for unary -) @param e2 second operand (optional) @return difference of e1 and e2, or negation of e1 for unary -