在 sml 中扩展 #

Question

假设我在 sml 中有一个非常大的列表，然后 sml 显示一些条目，然后开始显示 # 字符。

有人能告诉我如何查看整个列表吗？

Answer 1

假设这是 SML/NJ，您可以使用 printLength、printDepth 以及来自 Control.Print 结构。

以下是 控件文档的片段。 Print 结构：

printDepth
    The depth of nesting of recursive data structure at which ellipsis begins. 

printLength  
    The length of lists at which ellipsis begins. 

stringDepth
    The length of strings at which ellipsis begins. 

例如，我们可以通过更改 printLength 引用来更改不希望在 REPL 中显示的列表元素数量。

- Control.Print.printLength;
val it = ref 12 : int ref
- [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19];
val it = [1,2,3,4,5,6,7,8,9,10,11,12,...] : int list

- Control.Print.printLength := 18;
val it = () : unit
- [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19];
val it = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,...] : int list

- Control.Print.printLength := 100;
val it = () : unit
- [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19];
val it = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19] : int list

请注意，对于字符串和数据结构，省略号被写为散列“#”。例如，可以通过以下字符串看到这一点。请注意 val it = ... 行末尾的“#”，这是因为字符串的默认打印深度为 70 个字符：

- "Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.";
val it = "Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusm#" : string

- Control.Print.stringDepth;
val it = ref 70 : int ref

最后，这是一个如何在嵌套中看到这一点的示例数据结构：

- Control.Print.printDepth;
val it = ref 5 : int ref
- SOME (SOME (SOME (SOME (SOME (SOME (SOME 42))))));
val it = SOME (SOME (SOME (SOME (SOME #))))
  : int option option option option option option option

- Control.Print.printDepth := 10;
val it = () : unit
- SOME (SOME (SOME (SOME (SOME (SOME (SOME 42))))));
val it = SOME (SOME (SOME (SOME (SOME (SOME (SOME 42))))))
  : int option option option option option option option

两个建议的解决方案将导致打印整个列表，无论它有多长。

Answer 2

你可以做这样的事情：

(* Prints a list in its entirety.
 * ls is a list of type 'a list
 * f is a function that converts an 'a to string *)
fun printList f ls =
  let
    (* Prints the contents of the list neatly using f *)
    fun printContents []  = ()
      | printContents [x] = print (f x)
      | printContents (x::xs) = (print (f x ^ ", "); printContents xs)

    val _ = print "[";
    val _ = printContents ls;
    val _ = print "]\n"
    in
        ()
    end;

它的使用示例：

val ls = List.tabulate (1000, fn n => n);
printList Int.toString ls;

如果你想自动执行它，我怀疑你可以。如果我没记错的话，漂亮的打印机是特定于实现的，并且很可能不允许为多态类型安装漂亮的打印机。

Answer 3

Sabastian P. 代码的简短版本：

fun printList f ls =
    print ("[" ^ String.concatWith ", " (map f ls) ^ "]\n");