創建遞歸識別聯合值

Question

當我有這樣的代碼：

type HtmlNode = 
    | HtmlElement of name:string * attribute:HtmlAttribute list 
    | HtmlText of content:string 

and HtmlAttribute = 
    | HtmlAttribute of name:string * value:string * parent:HtmlNode 

let createElement name attrs = 
    let toAttributes element = [ for name, value in attrs -> HtmlAttribute(name, value, element)] 
    let rec element = HtmlElement(name, attributes) 
    and attributes = toAttributes element 
    element 

編譯器提供了以下錯誤：

Recursive values cannot appear directly as a construction of the type 'HtmlNode' within a recursive binding. This feature has been removed from the F# language. Consider using a record instead.

這是爲什麼？ [讓REC應該支持遞歸值，並與記錄的類似的東西作品的創作。

Answer 1

我不知道爲什麼會被改變，但一個解決方法是使用seq而不是list。

type HtmlNode = 
    | HtmlElement of name:string * attribute:HtmlAttribute seq 
    | HtmlText of content:string 

and HtmlAttribute = 
    | HtmlAttribute of name:string * value:string * parent:HtmlNode 

let createElement name attrs = 
    let rec element = HtmlElement(name, attributes) 
    and attributes = seq { for name, value in attrs -> HtmlAttribute(name, value, element) } 
    element