Miranda while 和 for 循环

发布于 2024-12-08 19:46:31 字数 152 浏览 0 评论 0原文

我正在寻找一种在 Miranda 中进行 while 循环或 for 循环的方法。

我正在尝试做类似的事情

while(blablanotfinished)
{
if(a=true)blabla
else blabla
}

原文

I'm looking for a way to do while-loops or for-loops in Miranda.

I'm trying to do something like

while(blablanotfinished)
{
if(a=true)blabla
else blabla
}

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成熟稳重的好男人 2024-12-15 19:46:31

Miranda 没有 while 或 for 循环（无论如何，如果没有可变状态，这就没多大意义）。在大多数情况下，您可以改用高阶函数。如果没有高阶函数可以满足您的需要，您可以使用递归。

例如，如果您在命令式语言中有以下 while 循环：

f(start) {
    x = start
    while( !finished(x) ) {
        x = next(x)  
    }
    return x
}

您可以在 Miranda 中递归地表达它，如下所示：

f x = if finished x then x else f (next x)

Miranda doesn't have while- or for-loops (which wouldn't make much sense without mutable state anyway). In most cases you can use higher order functions instead. In cases where there is no higher-order function which does what you need, you can use recursion.

For example if you have the following while-loop in an imperative language:

f(start) {
    x = start
    while( !finished(x) ) {
        x = next(x)  
    }
    return x
}

You would express it recursively in Miranda like this:

f x = if finished x then x else f (next x)

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温柔一刀 2024-12-15 19:46:31

函数式编程风格中的 while/repeat/for 循环如下所示：

while :: (*->bool) -> (*->*) -> * -> *
while p ff state
  = state                , if ~ (p state)
  = while p ff (ff state), otherwise

示例：将数字添加到其相反的位置，直到它成为回文。
提示：起始值 196 导致非常大的数字。

isPalindrome :: num -> bool
isPalindrome n = (str = reverse str) where str = shownum n

addPalindrome :: num -> num
addPalindrome n = n + rev where rev = (numval.reverse.shownum) n

test196 :: num -> num
test196 n = while ((~).isPalindrome) addPalindrome n

test = test196 89

我希望，有人仍然对戈弗/米兰达/哈斯克尔感兴趣。

安娜玛丽·佩森（德国）

while/repeat/for-loops in functional programming style look like this:

while :: (*->bool) -> (*->*) -> * -> *
while p ff state
  = state                , if ~ (p state)
  = while p ff (ff state), otherwise

Sample: Add number to its reverse until it is a palindrome.
Hints: Start value 196 leads to VERY big numbers.

isPalindrome :: num -> bool
isPalindrome n = (str = reverse str) where str = shownum n

addPalindrome :: num -> num
addPalindrome n = n + rev where rev = (numval.reverse.shownum) n

test196 :: num -> num
test196 n = while ((~).isPalindrome) addPalindrome n

test = test196 89

I hope, somebody is still interested in Gofer/Miranda/Haskell.

Annemarie Paysen (Germany)

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