How to account interest rate

[Dmitry V'yal]

Derek Atkins wrote:
> Hi,
> 
> "Dmitry V'yal" <akamaus at gmail.com> writes:
> 
>> Hello list,
>>
>> I'm trying make use of scheduled transactions to track money on my
>> bank deposit account. I'm studying how to use scheme scripting. The
>> biggest obstacle for me is the necessary api.
>>
>> I couldn't find any source of documentation. Can anyone give some
>> hints where to start?
> 
> The biggest problem with trying to do this is that the SX system does
> not have a "BalanceAsOfDate" function, so there's no way to compute
> interest based on the "current balance" of an accounts.

Not good..
Would it be hard to add it?
Is it feasible to build the functionality for accounting the interest 
rate on top of it? Or maybe there're some alternative approaches?

Dmitry