F# strange printfn problem -

-

I was playing with F # (Visual Studio 2010 Beta 1) around, and I wrote a small console script In which the user asked the input number 2 and one operator and then executed it. It works fine except for a small, but annoying thing: Sometimes my printfn instructions are ignored. I really have a breakpoint in the code to see the case.

Code snippet: 

  Convert (source: string) = Try System.Int32.Parse (Source) with:? System.FormatException - & gt; Printfn "'% s' is not a number!" Source; WaitForExitKey (); Give exit 1 read = printfn "Please enter a number."; Give System.Console.ReadLine num1: int = read () | & Gt; Printfn is running in the Convert / Print function ... Give num2: int = read () | & Gt; // Convert ... but this has not been taken care of

This is not the full source of the course, but I think it will be enough if you need the full source then Just tell.

So my question is very simple: what is the reason for this issue with printfn? Am I doing something wrong?

Thank you in advance, ShdNx

A partial explanation of what is happening , But the short and sweet version is that F # will execute any value on the declaration if it does not take the criteria. 

  read = printfn "Please enter a number." System.Console.ReadLine   
 Since  read  does not take any parameters, its instant announcement is executed and the return value of the function to the identifier  read < / Code>. 
 
 By coincidence, your return value is with a type of work  (unit -> string)  This result is because F # automatically if they do not pass all their parameters  ReadLine  one unit expects the parameter, but since it is not passed, you can actually  read  to the  readLine  function Force it. 
 
 The solution is as follows: 
 
  read () = // read a unit parameter printfn "Please enter the number." Since  read  takes a parameter, it is re-evaluated every time it is called. In addition, we are passing a parameter for  readLine  otherwise we will return the  ReadLine  function as a value.

Comments

Post a Comment

Popular posts from this blog

c++ - Linux and clipboard -

-
After selecting the copies of the buffer in Linux, after the text, we can click and paste the button between the mouse. I think there is a special buffer for this, I want to use it. Programming Language: C ++ Your Library: Qt Thanks. There is just one more correct answer than Paul Dixon, which answers your needs: / P > QClipboard * clipboard = QApplication :: clipboard (); CastString Selected Text = Clipboard-> Text (QClipboard :: Selection);
Read more

Visual Studio 2005: How to speed up builds when a VSMDI is open? -

-
Using Visual Studio 2005, if I open the test in VSMFI and try to run the tests, then sometimes the projects are ready. However, they run very slow. CPU 99% waste and output window VS Shows things associated with compiling it. Is there any way to fix this? It does not make any sense. It is not necessary to upgrade that we are a viable alternative to those people who have to deal with the legacy code. Did you try to upgrade SP1? I do not know of any specific problem in this area, but this will be the first change I tried to do.
Read more

booting ubuntu from usb using virtualbox -

-
I am trying to install Ubuntu on a USB, the problem is that I do not want to repeat the boot once, I want to keep my windows, but I want to boot Ubuntu using the virtualbox and USB to the Ubuntu Want to use my hard drive, but how? The virtualbox will not recognize USB as a hard drive when installing an ISO In virtualbox, you have to create a virtual hard disk. Make a USB drive and tell the virtual box to install a virtual hard drive that you just created. EDIT: To answer some more questions: In the new Virtual Disk dialog, click the button next to the location field, click on the button Virtual Disk on Flash Drive To access, click the arrow next to Save in the Select File in the window next to Save In, and you can access your flash drive from there. I recommend setting the image to be allocated dynamically, because the size of your flash drive is not available disk space. I name the image, then select that image to install Ubuntu in the Verbill box. The virtualbox will never...
Read more