PureEvalIOAsync
IO 是一个用来控制流程、隔离副作用的单子。
IOAsync 是它的异步版本，支持对 Promise 的包装。
此处是一个 IOAsync 单子使用的总例。
js
const getUserInfo = IOAsync(async () => {
const name = await fetchNameFromDatabase();
const age = await fetchAgeFromDatabase();
return { name, age };
});
const greetUser = (userInfo) => `Hello, ${userInfo.name}! You are ${userInfo.age} years old.`;
getUserInfo.map(greetUser).run().then(console.log).catch(console.error);const getUserInfo = IOAsync(async () => {
const name = await fetchNameFromDatabase();
const age = await fetchAgeFromDatabase();
return { name, age };
});
const greetUser = (userInfo) => `Hello, ${userInfo.name}! You are ${userInfo.age} years old.`;
getUserInfo.map(greetUser).run().then(console.log).catch(console.error);IOAsync
IOAsync 的构造函数，用来进行 IOAsync 的常规构造，传入的函数必须返回一个 Promise 对象。
- Type
- Example
js
IOAsync(async () => 1); //IOAsync 1IOAsync(async () => 1); //IOAsync 1IOAsync.map()
对 IOAsync 中的值进行映射。
- Type
- Example
js
IO(async () => 1).map(add(1)); //IOAsync 2IO(async () => 1).map(add(1)); //IOAsync 2IOAsync.chain()
在当前 IOAsync 任务后拼接新的 IOAsync 任务。
- Type
- Example
js
import { readFile, writeFile } from 'fs';
const myReadFile = (filename) =>
IOAsync(
() =>
new Promise((resolve, reject) => {
readFile(filename, 'utf8', (err, data) => {
if (err) reject(err);
else resolve(data);
});
})
);
const writeFile = (filename, data) =>
IOAsync(
() =>
new Promise((resolve, reject) => {
writeFile(filename, data, 'utf8', (err) => {
if (err) reject(err);
else resolve();
});
})
);
const program = myReadFile('input.txt')
.map((data) => data.toString().toUpperCase())
.chain((data) => writeFile('output.txt', data));
program.run();import { readFile, writeFile } from 'fs';
const myReadFile = (filename) =>
IOAsync(
() =>
new Promise((resolve, reject) => {
readFile(filename, 'utf8', (err, data) => {
if (err) reject(err);
else resolve(data);
});
})
);
const writeFile = (filename, data) =>
IOAsync(
() =>
new Promise((resolve, reject) => {
writeFile(filename, data, 'utf8', (err) => {
if (err) reject(err);
else resolve();
});
})
);
const program = myReadFile('input.txt')
.map((data) => data.toString().toUpperCase())
.chain((data) => writeFile('output.txt', data));
program.run();IOAsync.handle(Algebraic Effects)
handle 方法是一个代数效应(Algebraic Effects)的实现。
采用该方法可以挂载 perform 函数的内容到 IOAsync 上，进而在 effect 中通过 perform 函数执行。
- Type
- Example
js
//calc 1*x + 2*y + 3*z
function fooAsync(x, y, z) {
return IOAsync(async (perform) => {
const a = 1 * (await perform('x'));
const b = 2 * (await perform('y'));
const c = 3 * (await perform('z'));
return a + b + c;
})
.handle(match('x', x, 'y', y, 'z', z))
.run();
}
console.log(await fooAsync(1, 2, 3)); //14//calc 1*x + 2*y + 3*z
function fooAsync(x, y, z) {
return IOAsync(async (perform) => {
const a = 1 * (await perform('x'));
const b = 2 * (await perform('y'));
const c = 3 * (await perform('z'));
return a + b + c;
})
.handle(match('x', x, 'y', y, 'z', z))
.run();
}
console.log(await fooAsync(1, 2, 3)); //14IOAsync.run()
一个 IOAsync 单子在没有执行 run 方法之前都是不会执行的。
run 方法用来执行一个 IOAsync 单子。
WARNING
这个操作是 Unsafe 的。
- Type
- Example
js
import { readFile, writeFile } from 'fs';
const myReadFile = (filename) =>
IOAsync(
() =>
new Promise((resolve, reject) => {
readFile(filename, 'utf8', (err, data) => {
if (err) reject(err);
else resolve(data);
});
})
);
const writeFile = (filename, data) =>
IOAsync(
() =>
new Promise((resolve, reject) => {
writeFile(filename, data, 'utf8', (err) => {
if (err) reject(err);
else resolve();
});
})
);
const program = myReadFile('input.txt')
.map((data) => data.toString().toUpperCase())
.chain((data) => writeFile('output.txt', data));
program.run();import { readFile, writeFile } from 'fs';
const myReadFile = (filename) =>
IOAsync(
() =>
new Promise((resolve, reject) => {
readFile(filename, 'utf8', (err, data) => {
if (err) reject(err);
else resolve(data);
});
})
);
const writeFile = (filename, data) =>
IOAsync(
() =>
new Promise((resolve, reject) => {
writeFile(filename, data, 'utf8', (err) => {
if (err) reject(err);
else resolve();
});
})
);
const program = myReadFile('input.txt')
.map((data) => data.toString().toUpperCase())
.chain((data) => writeFile('output.txt', data));
program.run();