Custom .scm script: Query account balance

[Eric Wheeler]

Hello all,

I would like to update our invoice .scm template to include a balance from 
an account containing the customer's name (this is separate from any 
accounts receivable, it is a retainer liability account).

I tried digging through the account piechart.scm and the taxinvoice.scm to 
see if I can come up with a way to query the account something like this:

gnc:account-get-comm-balance-at-date append("Liabilities::Retainers::" coyname)

But I'm not sure how to pass today's date. It's been years since I've 
written scheme so any help would be greatly appreciated!

-Eric

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Eric Wheeler