Either

Example

package main

import (
    "fmt"
    "log"

    "golang.org/x/exp/constraints"

    "github.com/go-asset/generics/either"
    "github.com/go-asset/generics/list"
    "github.com/go-asset/generics/maybe"
)

func main() {
    result := list.FoldlIter(
        maybe.Nothing[int](),
        readFromUser(),
        add[string, int],
    )

    fmt.Println(result)
}

/*
 * Generic function, to add values (concatenation for string).
 */

 func add[L any, R constraints.Ordered](c maybe.Maybe[R], value either.Either[L, R]) maybe.Maybe[R] {
    if !value.IsRight() {
        log.Printf("Skip: %v\n", value.Left())

        return c
    }

    if c.IsNothing() {
        return maybe.Just(value.Right())
    }

    return maybe.Just(c.Value() + value.Right())
}

/*
 * Helper functions to generate content, like if it's coming from a user.
 */

func readFromUser() chan either.Either[string, int] {
    ch := make(chan either.Either[string, int])

    myList := []either.Either[string, int]{
        either.Right[string](12),
        either.Right[string](2),
        either.Left[string, int]("asd"),
        either.Right[string](8),
    }

    go func() {
        for _, v := range myList {
            ch <- v
        }

        close(ch)
    }()

    return ch
}