Functional Core の四つの例

package main

import (
    "fmt"

    "example.com/order_flow/glue/kaname"
    flow "example.com/order_flow/glue/orderflow"
    "example.com/order_flow/units"
)

…

func main() {
    events := []flow.Event{
        flow.EventAdd{Line: flow.Line{Sku: "pen", Qty: 2, Price: units.USDc(150)}},
        flow.EventAdd{Line: flow.Line{Sku: "ink", Qty: 1, Price: units.USDc(400)}},
        flow.EventPlace{On: kaname.Date{Year: 2026, Month: 10, Day: 22}},
        flow.EventPay{Amount: units.USDc(650)},
        flow.EventPay{Amount: units.USDc(700)},
        flow.EventShip{Tracking: "1Z-42"},
        flow.EventCancel{Reason: "too late"},
    }
    var order flow.Order = flow.OrderCart{}
    for _, event := range events {
        switch r := flow.Next(order, event).(type) {
        case kaname.Err[flow.Order, string]:
            fmt.Printf("%s: refused: %s\n", name(event), r.Error)
        case kaname.Ok[flow.Order, string]:
            order = r.Value
            fmt.Printf("%s: %s\n", name(event), name(order))
        }
    }
}

package main

import (
    "fmt"
    "maps"
    "slices"
    "strings"

    stock "example.com/stock_diff/glue/stockdiff"
)

func main() {
    before := map[string]int64{"ink": 4, "pen": 10, "pad": 2}
    after := map[string]int64{"pen": 7, "pad": 2, "tape": 3}
    for _, c := range stock.Changes(before, after) {
        switch c := c.(type) {
        case stock.ChangeAdded:
            fmt.Printf("added %s: %d\n", c.Sku, c.Qty)
        case stock.ChangeRemoved:
            fmt.Printf("removed %s: %d\n", c.Sku, c.Qty)
        case stock.ChangeChanged:
            fmt.Printf("changed %s: %d -> %d\n", c.Sku, c.Was, c.Now)
        }
    }
    today := stock.Moved(after, []stock.Move{{Sku: "pen", Qty: -7}, {Sku: "glue", Qty: 12}})
    var counts []string
    for _, sku := range slices.Sorted(maps.Keys(today)) {
        counts = append(counts, fmt.Sprintf("%s %d", sku, today[sku]))
    }
    fmt.Println("after the day: " + strings.Join(counts, ", "))
    fmt.Println("to reorder: " + strings.Join(slices.Sorted(maps.Keys(stock.ToReorder(today, 5))), ", "))
}

package main

import (
    "fmt"
    "strings"

    "example.com/handles/glue/handles"
    "example.com/handles/glue/kaname"
)

func main() {
    for _, typed := range []string{" Grace Hopper", "9", "Root", "ünïcode"} {
        switch r := handles.Handle(typed).(type) {
        case kaname.Ok[string, []string]:
            fmt.Printf("%q -> %s\n", typed, r.Value)
        case kaname.Err[string, []string]:
            fmt.Printf("%q -> refused: %s\n", typed, strings.Join(r.Error, "; "))
        }
    }
    for _, typed := range []string{"Ada Lovelace#42", "ada#0"} {
        switch r := handles.TagFn(typed).(type) {
        case kaname.Ok[handles.Tag, []string]:
            fmt.Printf("%q -> %s #%d\n", typed, r.Value.Handle, r.Value.Number)
        case kaname.Err[handles.Tag, []string]:
            fmt.Printf("%q -> refused: %s\n", typed, strings.Join(r.Error, "; "))
        }
    }
}

package main

import (
    "fmt"
    "strings"

    "example.com/catalog/glue/catalog"
    "example.com/catalog/units"
)

func main() {
    garden := catalog.Category{
        Name: "Garden",
        Children: []catalog.Category{
            {Name: "Hand Tools", Items: []catalog.Item{{Sku: "sp-1", Name: "Spade", Price: units.USDc(1999)}, {Sku: "tr-2", Name: "Trowel", Price: units.USDc(899)}}},
            {Name: "Seeds", Children: []catalog.Category{{Name: "Bulbs"}}},
            {Name: "Hoses", Items: []catalog.Item{{Sku: "hr-1", Name: "Hose reel", Price: units.USDc(4500)}}},
        },
    }
    for _, p := range catalog.Paths(garden) {
        fmt.Println(p)
    }
    if kept := catalog.Pruned(garden); kept == nil {
        fmt.Println("kept: nothing")
    } else {
        fmt.Println("kept: " + strings.Join(catalog.Names(*kept), ", "))
    }
    fmt.Println("slugs: " + strings.Join(catalog.Names(catalog.Slugged(garden)), ", "))
    if c := catalog.Cheapest(garden); c == nil {
        fmt.Println("cheapest: none")
    } else {
        fmt.Printf("cheapest: %s, %d cents\n", c.Name, c.Price)
    }
}