Penny.Lincoln.Bits.Qty

Penny quantities. A quantity is simply a count (possibly fractional) of something. It does not have a commodity or a Debit/Credit.

Documentation

data Qty

A quantity is always greater than zero. Various odd questions happen if quantities can be zero. For instance, what if you have a debit whose quantity is zero? Does it require a balancing credit that is also zero? And how can you have a debit of zero anyway?

I can imagine situations where a quantity of zero might be useful; for instance maybe you want to specifically indicate that a particular posting in a transaction did not happen (for instance, that a paycheck deduction did not take place). I think the better way to handle that though would be through an addition to DebitCredit - maybe DebitCredit/Zero. Barring the addition of that, though, the best way to indicate a situation such as this would be through transaction memos.

Instances

Eq Qty

Ord Qty

Show Qty

unQty :: Qty -> Decimal

Unwrap a Qty to get the underlying Decimal. This Decimal will always be greater than zero.

partialNewQty :: Decimal -> Qty

Make a new Qty. This function is partial. It will call error if its argument is less than or equal to zero.

newQty :: Decimal -> Maybe Qty

Make a new Qty. Returns Nothing if its argument is less than zero.

add :: Qty -> Qty -> Qty

subt :: Qty -> Qty -> Maybe Qty

mult :: Qty -> Qty -> Qty

zero :: Qty

data Difference

Constructors

LeftBiggerBy Qty

RightBiggerBy Qty

Equal

difference :: Qty -> Qty -> Difference

Subtract the second Qty from the first.