Common Lisp library for working with commoditized amounts and balances
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CAMBL

Commoditized Amounts and Balances

This library provides a convenient facility for working with commoditized values. It does not allow compound units – and so is not suited for scientific operations – but does work rather nicely for the purpose of financial calculations.

The primary entry point to using this library is the creation of VALUES, which may be of many different types. These VALUES are then used as arguments to a set of basic mathematical OPERATIONS, which also yield VALUES. However, the type of the result may not be the same type as either of the operands.

For example, let’s say you want to create a figure representing 10 US dollars. You then add an INTEGER to this amount, the number 200. The result of such an operation will be an amalgam of the two units involved: Dollars, and No-units. This dual-commodity value is represented as a BALANCE object, whose printed form shows each commodity amount on its own line. For example:

(let ((value (cambl:amount "$100.00")))
    (princ (cambl:format-value (cambl:add value 200))))
  => 200
     $100.00

This library aims to provide convenient access to commoditized math; that is: math involving commodity units. Unlike scientific units, there is no concept of “compound” units. If you divide 1kg by 1m, you do not get “1 kg/m”, but “1 kg” (the unit of the second operand is ignored for multiplication and division). The intended use of this library is in situations such as computing financial transactions.