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

[Peter Achten]

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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