我无法理解下面的fmap实例.有人可以解释一下fmap做什么(在这种情况下)以及如何使用它？或者写一点混淆？谢谢!
newtype Parser a = P { getParser :: String -> Maybe (a, String) }
instance Functor Parser where
fmap f (P p) = P $ \s -> fmap (applyToFirst f) $ p s
{-|
Applies a function to the first component of a pair.
-}
applyToFirst :: (a -> b) -> (a, c) -> (b, c)
applyToFirst f (x, y) = (f x, y)
我有以下几点Repeater：
Repeater{
id: rainDropId
model: 200
delegate: Rectangle {
x: Math.floor(Math.random() * windowId.width)
y: Math.floor(Math.random() * windowId.height)
property int mLayer: Math.floor(Math.random() * 4) + 1
property double mYSpeed: -2.0 * mLayer
width:5
height:5
color: "#3399FF"
radius: width*0.5
}
}
我有一个Timer. 我想Repeater根据自己的属性修改所有元素的位置。我怎样才能rainDropId[index]从Timer?
谢谢
我有这段代码
#include <stdio.h>
typedef signed long long v2signed_long
__attribute__ ((__vector_size__ (sizeof(signed long long) * 2)));
int main()
{
v2signed_long v = {4611686018427387904LL, -9223372036854775808LL};
printf("%lli, %lli\n", v[0], v[1]);
return 0;
}
这给出了以下警告（相关问题没有帮助）：
:7:45: warning: integer literal is too large to be represented in
a signed integer type, interpreting as unsigned
[-Wimplicitly-unsigned-literal]
v2signed_long v = {4611686018427387904LL, -9223372036854775808LL};
有没有办法解决这个警告？谢谢！
我有这个功能:
data Memory = Memory
{visited::[Point]
,dfsstack::[Point]
,currentPoz::Point
}deriving(Eq)
perceiveAndAct :: SVal -> [Cardinal] -> a -> (Action, a)
perceiveAndAct s cs m
| elem W cs == True && elem N cs == True && elem E cs == True && elem S cs == False = (Just S, Memory (visited m) (dfsstack m) (currentPoz m))
把m而不是 Memory (visited m) (dfsstack m) (currentPoz m)工作正常,否则它给了我:
Couldn't match expected type `(a, b)'
against inferred type `Memory -> Point'
In the …您好我正在尝试使用imbricated条件,但我得到解析错误:
parse error on input ‘|’
isAssignMent::String->Bool
isAssignMent a
| a == "" = False
| otherwise
| (head trimmed) == '=' = True
| otherwise = False
where
trimmed = trimRightSide a [' ', '\n']
我究竟做错了什么？谢谢
我需要比较Windows新行字符('\ r \n'),但我得到了
lexical error in string/character literal at character '\\'
['\r\n']
我怎么解决这个问题？
谢谢!
我想清除treeView选择，我使用
static_cast<QTreeView*>(mContext)->selectionModel()->clear();， static_cast<QTreeView*>(mContext)即我正在谈论的树，但是仍然存在次浅蓝色选择，如何完全删除选择？
谢谢！
我有一个上下文菜单,我只想在QTreeView中的项目顶部出现.什么时候在空白的顶部,我什么都不想做.这就是我现在所拥有的
void MainTreeViewController::showContextMenu(const QPoint& pos)
{
QPoint globalPos = mtreeView->mapToGlobal(pos);
QMenu rightClickMenu;
for(int i = 0; i < kCharModelRightClickOptionsCount; ++i){
rightClickMenu.addAction("Menu option");
}
QAction* selectedItem = rightClickMenu.exec(globalPos);
if (selectedItem){
}
}
谢谢!
当我收到UDP消息(使用boost :: asio :: ip :: udp)时,如何通过boost检索IP地址？
谢谢!
我想从QTreeView的条目生成右键菜单.目前我尝试了这个,但我不希望整个treeView生成右键单击然后我过滤鼠标所在的位置.我希望从条目生成信号.
connect(mtreeView, SIGNAL(customContextMenuRequested(const QPoint&)),
this, SLOT(showContextMenu(const QPoint&)));
谢谢!