5.19.return.md

5.19.return

一个return表达式可以返回也可以不返回一个值表达式：

A return expression can come with or without an value expression:

return; 
return expression; 

它会离开它被声明所在的控制流最深的函数，当局部函数（第5.11节）被调用时需要被区别：

It leaves the control-flow of the innermost function it is declared in, which has to be distinguished when local functions (5.11) are involved:

function f1() { 
    function f2() { 
        return; 
    } 
    f2(); 
    expression; 
} 

return会离开局部函数 f2，但不会离开 f 1，意味着 expression仍然会被执行。

The return leaves local function f2, but not f1, meaning expression is still evaluated.

如果 return 不带值表达式使用，类型工具确保函数返回类型会返回Void 。如果它有一个值表达式，类型工具 统一（第3.5节）它的类型为它所返回的函数的返回类型（显式指定或者通过前面的return表达式推断）。

If return is used without a value expression, the typer ensures that the return type of the function it returns from is of Void. If it has a value expression,the typer unifies(3.5) its type with the return type (explicitly given or inferred by previous return expressions) of the function it returns from.