PureEvalIOAsync
IOAsync is an asynchronous version of the IO monad used for controlling flow and isolating side effects. It supports wrapping around Promises.
Here is a general example of using the IOAsync monad:
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
The constructor function for IOAsync, used for standard IOAsync construction. The function passed in must return a Promise object.
- Type
- Example
js
IOAsync(async () => 1); //IOAsync 1IOAsync(async () => 1); //IOAsync 1IOAsync.map()
Maps the value inside IOAsync.
- Type
- Example
js
IOAsync(async () => 1).map(add(1)); //IOAsync 2IOAsync(async () => 1).map(add(1)); //IOAsync 2IOAsync.chain()
Chains a new IOAsync task after the current one.
- 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)
The handle method is an implementation of Algebraic Effects.
This method allows the content of the perform function to be attached to IOAsync, allowing the perform function to be executed within the effect.
- 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()
An IOAsync monad will not execute until the run method is called.
The run method is used to execute an IOAsync monad.
WARNING
This operation is Unsafe.
- 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();