[clean-list] Help Please: Beginner to Clean.. Console I/O

[Khurram Khan]

Dear Peter

Thanks for taking time out and translating the C++ code for us. It was very useful and your explanations as well. We all appriciate your and other members of clean-list's contribution, who helped us understand things.

Regards
Khurram


Date: Mon, 9 May 2011 14:11:20 +0200
From: P.Achten at cs.ru.nl
To: kkjcid at hotmail.com
CC: clean-list at cs.ru.nl
Subject: Re: [clean-list] Help Please: Beginner to Clean.. Console I/O



  


    
  
  
    Dear Khurram and everybody else,

    

    ...back from holidays...

    

    Thanks everybody for the excellent explanations! For your
    convenience, I've included the Clean version of your C++ example in
    this message below. I hope that it demonstrates that basic console
    I/O in Clean is not that different from basic console I/O in C++.
    The key differences are that you must pass around the modified
    environments (notably world and console), and that basic Clean file
    I/O does not offer a >> operation as C++ does. So, for the
    input of integers I use freadline (which reads an entire line
    including terminating newline character), and a local utility
    function, turn_to_Int, that first removes the trailing newline
    character (str%(0,size str-2)) and then uses the standard toInt
    function to obtain the integer value. Note that if you forget to
    eliminate the trailing newline character, toInt will produce 0. This
    is actually also the case for any input that does not match an
    integer denotation exactly (for instance, toInt "100       " also
    returns 0). 

    

    Regards,

    Peter

    

    On 5/4/2011 3:46 PM, Khurram Khan wrote:
    
      
      
      Many thanks for your reply. I've read through let-before section
      and it has developed a bit more understanding now on what is
      happening the "hello1" example. I should've been more specific
      with my question last time. Actually me and a couple of my
      classmates are working together to learn Clean and finding it very
      hard to understand I/O operations in Clean. We believe that
      probably Clean user-guides are written for people who have some
      previous knowledge of functional programming, but we are very keen
      to learn the language and we have up til now found it very
      interesting, specially the fact that it, in many ways, resembles
      to how you write functions in pure mathematical sense. 

      

      However, as we are so much used to C/C++, we were thinking that
      Clean must also have some basic way of doing simple I/O
      operations, like we have "cout" and "cin" in C++, but we are
      unable to develop that understanding from examples "hello1" and
      "hello2". We have also looked at some code provided with Clean IDE
      software as examples, but those examples are also on
      intermediate/advanced level, compared to where we are at the
      moment. 

      

      We were thinking if its possible for you to translate this simple
      code of C++ in Clean and provide some comments on it as well. We
      are certain that it will help solve I/O dilemma for us, and we are
      deeply thankful for the time you take out to help us.

      

      /* Just a simple program performing input/output to user console
      and performing a calculation*/

      

      void main ()

      {

            double FirstNumber=0.0;

            double SecondNumber=0.0;

            double ThirdNumber =0.0;

            double Result =0.0;

      

            cout << "This program will accept three integer
      numbers and find their average value\n\n";

          

            cout << "Enter First Number: ";

            cin >> FirstNumber;

      

            cout << "\nEnter Second Number: ";

            cin >> SecondNumber;

      

            cout << "\nEnter Third Number: ";

            cin >> ThirdNumber;

      

            Result = (FirstNumber+SecondNumber+ThirdNumber)/3;

      

            cout << "\nThe result is : " << Result <<
      "\n\n";

      

            system("pause");

      }

    
    

    ===========================

    Start                :: *World -> *World

      Start world

      # (console,world)    = stdio world

      # console            = console <<< "This program will
      accept three integer numbers and find their average value\n\n"

      # console            = console <<< "Enter First Number: "

      # (i1,console)       = freadline console

      # console            = console <<< "\nEnter Second
      Number: "

      # (i2,console)       = freadline console 

      # console            = console <<< "\nEnter Third Number:
      "

      # (i3,console)       = freadline console

      # (i1,i2,i3)         = (turn_to_Int i1,turn_to_Int i2,turn_to_Int
      i3)

      # result             = fromInt (i1+i2+i3) / 3.0

      # console            = console <<< "\nThe result is : "
      <<< result <<< "\n\n"

      # (ok,world)         = fclose console world

      | not ok             = abort "Could not close stdio.\n"

      | otherwise          = world

      

      turn_to_Int str      = toInt (str%(0,size str-2))

    ===========================

    

    

    p.s.: the evaluation of every Clean program is driven by the need to
    print the outcome of the Start-function. In case of these 
    interactive programs, the outcome is a value of type World.
    Internally, the World is represented by an integer of value 65536.
    This is the reason why that value is also printed on the console. As
    commented by Isaac, you can suppress printing this result via the
    CleanIDE.

    
 		 	   		  
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