如何在 SML 中获取整数作为用户输入

Question

I'm trying to get a number from a user. That number is then used to call another function randomList(n) which takes the given number and uses it. I keep getting the error exception option. I've read that adding SOME to the variable declaration or valOf can fix this issue, but it is not working for me. What do I need to change?

fun getNumber() = 
print "Please enter the number of integers: ";
let
    val str = valOf (TextIO.inputLine TextIO.stdIn)
    val i : int = valOf (Int.fromString str)
    in 
    randomList(i)
end;
getNumber();

Answer 1

这里的问题是 fun getNumber() 只包含下一行的 print 语句。如果您希望 print 和 let 都属于 getNumber().

，则需要将它们括在括号内

例如，以下代码编译并回显通过 stdin 传入的输入整数：

fun getNumber() = (
print "Please enter the number of integers: ";
let
    val str = valOf (TextIO.inputLine TextIO.stdIn)
    val i : int = valOf (Int.fromString str)
in
    print(Int.toString(i))
end
);
getNumber();

如何在 SML 中获取整数作为用户输入

How to get an integer as user input in SML

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