Ocaml運營商在匿名函數

Question

我想寫一個函數，將解析一個列表並創建一個新的列表，其中包含我想在這種情況下的名稱的話。

我可以令狀的功能一個名字e.g

let extract_name (lst : string list) : string list = 
List.filter (fun x -> x = "George") (lst) 

當我試圖寫它不止一個名字，我得到的錯誤。我重新安排了幾次括號，但仍然出現錯誤。

let extract_name (lst : string list) : string list = 
List.filter (fun x -> x = ("George" || "Victoria")) (lst) 

錯誤

let extract_name (lst : string list) : string list = 
List.filter (fun x -> x = "George" || "Victoria") (lst) 
;; 
Characters 93-103: 
List.filter (fun x -> x = "George" || "Victoria") (lst) 
             ^^^^^^^^^^ 
Error: This expression has type string but an expression was expecte of type bool 
# let extract_name (lst : string list) : string list = 
List.filter (fun x -> x = ("George" || "Victoria")) (lst);; 
Characters 82-90: 
List.filter (fun x -> x = ("George" || "Victoria")) (lst);; 
          ^^^^^^^^ 
Error: This expression has type string but an expression was expected  of type bool 

如何解決這個問題？

Answer 1

您試圖在兩個字符串上應用布爾||運算符，這不起作用並導致類型錯誤。您需要單獨測試與x平等的兩個字符串，然後或者結果：

List.filter (fun x -> (x = "George") || (x = "Victoria")) lst