Module documented
Interface digest 5e3d4b05eda38000c6745c9cb47ab260 · 9/9 published names documented
Types
Money
type Money = newtype[Int]An amount of money in minor units — pence, cents — never a float.
A newtype rather than an alias, so it cannot be passed where a plain `Int` is expected: §3.1's "ids of different entities must not be interchangeable" is about amounts too.
Line
model LineOne line on an order: a product, bought some number of times.
| Field | |
|---|---|
sku: Str | What was bought. Opaque here; the catalogue owns the meaning. |
quantity: Int | How many. A line with a quantity of zero is legal and contributes nothing. |
unit_price: Money | The price of one unit when the line was written, not the price today. |
Adjustment
union AdjustmentWhat changes the amount payable, beyond the lines themselves.
| Variant | |
|---|---|
Discount(amount: Money) | A flat reduction. |
Shipping(cost: Money) | Carriage. Free delivery is `Shipping(Money(0))` rather than the absence of this variant. |
Names
| Name | Runs on | Effects |
|---|---|---|
apply_adjustment | any | no effects |
chargeable | any | no effects |
chargeable_count | any | no effects |
line_total | any | no effects |
minor_units | any | no effects |
payable | any | no effects |
apply_adjustment
apply_adjustment(running: Int, adjustment: Adjustment) -> Intdefon anyno effects
What one adjustment does to a running total — a discount subtracts, shipping adds.
chargeable
chargeable(lines: list[Line]) -> list[Line]defon anyno effects
The lines that would actually be charged for — quantity above zero.
`filter_list` is effect-polymorphic (§3.2), so this is pure exactly because its predicate is.
chargeable_count
chargeable_count(lines: list[Line]) -> Intdefon anyno effects
How many lines would be charged for.
line_total
line_total(line: Line) -> Intdefon anyno effects
What one line costs: unit price times quantity.
minor_units
minor_units(m: Money) -> Intdefon anyno effects
Read the minor units out of a `Money`.
The one place the newtype is opened, so a change of representation is a change here rather than everywhere an amount is arithmetic.
payable
payable(line: Line, adjustment: Adjustment) -> Intdefon anyno effects
The amount payable for one line under one adjustment.