纯错误处理
最后更新于：2022-04-02 04:17:56
[TOC]
## “纯”错误处理
- `throw/catch`并不十分“纯”
- 可以使用`Either` 处理纯函数
```
var Left = function(x) {
this.__value = x;
}
Left.of = function(x) {
return new Left(x);
}
Left.prototype.map = function(f) {
return this;
}
var Right = function(x) {
this.__value = x;
}
Right.of = function(x) {
return new Right(x);
}
Right.prototype.map = function(f) {
return Right.of(f(this.__value));
}
```
Left 和 Right 是我们称之为 Either 的抽象类型的两个子类
实例
```
var moment = require('moment');
// getAge :: Date -> User -> Either(String, Number)
var getAge = curry(function(now, user) {
var birthdate = moment(user.birthdate, 'YYYY-MM-DD');
if(!birthdate.isValid()) return Left.of("Birth date could not be parsed");
return Right.of(now.diff(birthdate, 'years'));
});
getAge(moment(), {birthdate: '2005-12-12'});
// Right(9)
getAge(moment(), {birthdate: 'balloons!'});
// Left("Birth date could not be parsed")
```
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