Question

如果我的Task有Either err b表示正确（成功）值，我该如何组合/合并/转换它们，以便成功值直接在{{1}中可用}，没有包裹在.fork()中？

Either

Answer 1

这就是我要做的事情：

var Task   = require("data.task");
var Either = require("data.either");

   // eitherYayNay :: Bool -> Either String String
const eitherYayNay = bool =>
    bool ?
        Either.Right("yay") :
        Either.Left("nay");

   // theTask :: Bool -> Task a (Either String String)
const theTask = bool => Task.of(eitherYayNay(bool));

   // niceTask :: Bool -> Task String String
const niceTask = bool => theTask(bool).chain(makeNice);

   // makeNice :: Either String String -> Task String String
const makeNice = either =>
    either.isRight ?
        Task.of(either.value) :
        Task.rejected(either.value);

const fork = bool => niceTask(bool).fork(onError, onValue);

const onError = error => console.log("Error: " + error);

const onValue = value => console.log("Value: " + value);

fork(true);  // Value: yay
fork(false); // Error: nay

参见演示：

var eitherYayNay = function (bool) {
    return bool ?
        Either.Right("yay") :
        Either.Left("nay");
};

var theTask = function (bool) {
    return Task.of(eitherYayNay(bool));
};

var niceTask = function (bool) {
    return theTask(bool).chain(makeNice);
};

var makeNice = function (either) {
    return either.isRight ?
        Task.of(either.value) :
        Task.rejected(either.value);
};

var fork = function (bool) {
    return niceTask(bool).fork(onError, onValue);
};

var onError = function (error) {
    alert("Error: " + error);
}

var onValue = function (value) {
    alert("Value: " + value);
}

fork(true);  // Value: yay
fork(false); // Error: nay

<script src="https://cdn.rawgit.com/aaditmshah/0b27bf3abfaba225b479/raw/f9c6af5e548d27c0d1932b80a9af7e0568c4a89e/task.js"></script>
<script src="https://cdn.rawgit.com/aaditmshah/5bf5e66c37663f3777ee/raw/3110fa24652ed42f005ebc40a39b5138db0063f9/either.js"></script>

希望有所帮助。

可以将`Either`类型转换为`Task`类型吗？

1 个答案: