[Javascript Crocks] Create a Maybe with a `safe` Utility Function

最新推荐文章于 2025-08-23 02:53:08 发布

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最新推荐文章于 2025-08-23 02:53:08 发布

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文章标签： javascript ViewUI

原文链接：http://www.cnblogs.com/Answer1215/p/9026265.html

本文介绍了一种使用安全函数创建Maybe实例的方法，并通过提供自定义的谓词函数实现了灵活的数据类型验证。文中还展示了如何利用高阶函数进行类型检查，并使用了Crocks库简化这一过程。

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In this lesson, we’ll create a safe function that gives us a flexible way to create Maybes based on a value and a predicate function that we supply. We’ll verify its behavior with values that satisfy the predicate, and values that do not.

We can write more functional approach, for example write predicate functions:

const isNumber = n => typeof n === 'number' ? Maybe.Just(n) : Maybe.Nothing();
const isString = s => typeof s === 'string' ? Maybe.Just(s) : Maybe.Nothing();

High order function:

const safe = pred => val => pred(val);

const safeNum = safe(isNumber);
const safeStr = safe(isString);

Those functions are useful when we want use in large scale application, because those are composable.

Full code demo:

const {inc, upper} = require('./utils');
const Maybe = require('crocks/Maybe');

const isNumber = n => typeof n === 'number' ? Maybe.Just(n) : Maybe.Nothing();
const isString = s => typeof s === 'string' ? Maybe.Just(s) : Maybe.Nothing();
const safe = pred => val => pred(val);

const safeNum = safe(isNumber);
const safeStr = safe(isString);

const inputN = safeNum(2); // Just 3 -> 3
const inputS = safeStr('test'); //  Just TEST -> TEST
const input = safeStr(undefined); // Nothing -> 0

const result = inputS
    .map(upper)
    .option("");

console.log(result);

Crocks lib also provides those functions, you actually don't need to write it by yourself.

https://evilsoft.github.io/crocks/docs/functions/predicate-functions.html

const {inc, upper} = require('./utils');
const Maybe = require('crocks/Maybe');
const safe = require('crocks/Maybe/safe');
const { isNumber, isString} = require('crocks/predicates');

/*
const isNumber = n => typeof n === 'number' ? Maybe.Just(n) : Maybe.Nothing();
const isString = s => typeof s === 'string' ? Maybe.Just(s) : Maybe.Nothing();
const safe = pred => val => pred(val);
*/
const safeNum = safe(isNumber);
const safeStr = safe(isString);

const inputN = safeNum(2); // Just 3 -> 3
const inputS = safeStr('test'); //  Just TEST -> TEST
const input = safeStr(undefined); // Nothing -> 0

const result = inputS
    .map(upper)
    .option("");

console.log(result);