小编mbr*_*sen的帖子

在以下Haskell代码中:

data Cmd =  
    CmdExit |  
    CmdOther  
    deriving (Read, Show)

guiString2Cmd s =  
    (return (read s :: Cmd)) `catch` \(e :: SomeException) -> return CmdExit

如果我做:

guiString2Cmd "CmdOther"

一切正常.但是,如果我这样做:

guiString2Cmd "some wrong string"

代码崩溃而不是评估为CmdExit.

如何让代码处理异常而不是崩溃？

通过直接将定义和法律翻译成Haskell,我很开心学习类别理论.Haskell当然不是Coq,但它帮助我获得了类别理论的直觉.我的问题是:以下是将一个类别的定义合理地"翻译"到Haskell中吗？

{-
  The following definition of a category is adapted from "Basic Category Theory" by Jaap van Oosten:

  A category is given by a collection of objects and a collection of morphisms.

  Each morphism has a domain and a codomain which are objects.

  One writes f:X->Y (or X -f-> Y) if X is the domain of the morphism f, and Y its codomain.

  One also writes X = dom(f) and Y = cod(f)

  Given two morphisms f and g such …

以下Haskell代码是一个简单的"控制台IO"DSL:

data Ap a = Ap { runAp :: ApStep a }

data ApStep a =
    ApRead   (String -> Ap a)
  | ApReturn a
  | ApWrite  String (Ap a)

ioRead    k   = Ap $ ApRead k
ioReturn  a   = Ap $ ApReturn a
ioWrite   s k = Ap $ ApWrite s k
ioWriteLn s   = ioWrite (s ++ "\n")

apTest =
  ioWriteLn "Hello world!" $
  ioRead $ \i ->
  ioWriteLn ("You wrote [" ++ i ++ "]") $
  ioReturn 10 …

如何在没有VS 2008将文件复制到项目文件夹的情况下将现有C#文件添加到VS 2008 C#项目中？

将现有C++文件添加到C++项目时,VS 2008不会复制文件.它只是使用文件路径.