PureEvalIO (Monad)
IO is a monad used for controlling flow and isolating side effects.
Here is a general example of using the IO monad:
js
import { readFileSync } from 'fs';
const myReadFileSync = (path) => IO(() => fs.readFileSync(path, 'utf8'));
const print = (message) => IO(() => console.log(message));
const program = myReadFileSync('./example.txt').chain((content) => print(content));
program.run();import { readFileSync } from 'fs';
const myReadFileSync = (path) => IO(() => fs.readFileSync(path, 'utf8'));
const print = (message) => IO(() => console.log(message));
const program = myReadFileSync('./example.txt').chain((content) => print(content));
program.run();IO
The IO constructor function, used for standard IO construction. The value passed in must be a function.
- Type
- Example
js
IO(() => 1); //IO 1IO(() => 1); //IO 1IO.map()
Maps the value inside IO.
- Type
- Example
js
IO(() => 1).map(add(1)); //IO 2IO(() => 1).map(add(1)); //IO 2IO.chain()
Chains a new IO task after the current one.
- Type
- Example
js
const readFile = (filename) => IO(() => fs.readFileSync(filename, 'utf-8'));
const parseJSON = (str) => IO(() => JSON.parse(str));
const getProp = (prop) => (obj) => IO(() => obj[prop]);
const example = readFile('example.json')
.chain(parseJSON)
.chain(getProp('data'))
.map((data) => data.toUpperCase())
.run();
console.log(example);const readFile = (filename) => IO(() => fs.readFileSync(filename, 'utf-8'));
const parseJSON = (str) => IO(() => JSON.parse(str));
const getProp = (prop) => (obj) => IO(() => obj[prop]);
const example = readFile('example.json')
.chain(parseJSON)
.chain(getProp('data'))
.map((data) => data.toUpperCase())
.run();
console.log(example);IO.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 IO, allowing the perform function to be executed within the effect.
- Type
- Example
js
//calc 1*x + 2*y + 3*z
function foo(x, y, z) {
return IO((perform) => {
const a = 1 * perform('x');
const b = 2 * perform('y');
const c = 3 * perform('z');
return a + b + c;
})
.handle(match('x', x, 'y', y, 'z', z))
.run();
}
console.log(foo(1, 2, 3)); //14//calc 1*x + 2*y + 3*z
function foo(x, y, z) {
return IO((perform) => {
const a = 1 * perform('x');
const b = 2 * perform('y');
const c = 3 * perform('z');
return a + b + c;
})
.handle(match('x', x, 'y', y, 'z', z))
.run();
}
console.log(foo(1, 2, 3)); //14IO.run()
An IO monad will not execute until the run method is called.
The run method is used to execute an IO monad.
WARNING
This operation is Unsafe.
- Type
- Example
js
const readFile = (filename) => IO(() => fs.readFileSync(filename, 'utf-8'));
const parseJSON = (str) => IO(() => JSON.parse(str));
const getProp = (prop) => (obj) => IO(() => obj[prop]);
const example = readFile('example.json')
.chain(parseJSON)
.chain(getProp('data'))
.map((data) => data.toUpperCase())
.run();
console.log(example);const readFile = (filename) => IO(() => fs.readFileSync(filename, 'utf-8'));
const parseJSON = (str) => IO(() => JSON.parse(str));
const getProp = (prop) => (obj) => IO(() => obj[prop]);
const example = readFile('example.json')
.chain(parseJSON)
.chain(getProp('data'))
.map((data) => data.toUpperCase())
.run();
console.log(example);