![Format Specifications
• Used for formatting the input or output,
• These are strings with % markers indicating format
placeholders.
• The syntax of a Format placeholders is −
%[flags][width][.precision]type](https://image.slidesharecdn.com/consoleclass-200516110020/85/F-Console-class-7-320.jpg)
![Type
Type Description
%o Formats any basic integer type formatted as an unsigned octal integer.
%e, %E, %f,
%F, %g, %G
Formats any basic floating point type (float, float32) formatted using a C-style floating point format
specifications.
%e, %E Formats a signed value having the form [-]d.dddde[sign]ddd where d is a single decimal digit, dddd is one or
more decimal digits, ddd is exactly three decimal digits, and sign is + or -.
%f Formats a signed value having the form [-]dddd.dddd, where dddd is one or more decimal digits. The number of
digits before the decimal point depends on the magnitude of the number, and the number of digits after the
decimal point depends on the requested precision.
%g, %G Formats a signed value printed in f or e format, whichever is more compact for the given value and precision.
%M Formats a Decimal value.
%O Formats any value, printed by boxing the object and using its ToString method.
%A, %+A Formats any value, printed with the default layout settings. Use %+A to print the structure of discriminated
unions with internal and private representations.](https://image.slidesharecdn.com/consoleclass-200516110020/85/F-Console-class-10-320.jpg)
![ABC
abc
Cat
Dog
bird
fish
File.txt
O/P
["ABC"; "abc"; "Cat"; "Dog"; "bird"; "fish"]
seq ["ABC"; "Cat"; "Dog"]](https://image.slidesharecdn.com/consoleclass-200516110020/85/F-Console-class-23-320.jpg)
![Calling Delegates
for (a, b) in [ (100, 200); (10, 20) ] do
printfn "%d + %d = %d" a b (InvokeDelegate1 del1 a b)
printfn "%d - %d = %d" a b (InvokeDelegate2 del2 a b)
printfn "%d + %d = %d" a b (InvokeDelegate1 del3 a b)
printfn "%d - %d = %d" a b (InvokeDelegate2 del4 a b)](https://image.slidesharecdn.com/consoleclass-200516110020/85/F-Console-class-38-320.jpg)
F# Console class
- 2. F# - Basic I/O Console Class Basic I/O System.IO Files & Directories Streams
- 3. F# - Basic I/O • Basic Input Output includes − 1. Reading from and writing into console. 2. Reading from and writing into file.
- 4. Core.Printf Module • We have used the various form of functions for writing into the console such as printf and the printfn. • Apart from the above functions, we have also seen the Core.Printf module of F# which has various other methods for printing and formatting using % markers as placeholders.
- 5. Core.Printf Module printf : TextWriterFormat<'T> → 'T Prints formatted output to stdout. printfn : TextWriterFormat<'T> → 'T Prints formatted output to stdout, adding a newline. sprintf : StringFormat<'T> → 'T Prints to a string by using an internal string buffer and returns the result as a string. fprintfn : TextWriter → TextWriterFormat<'T> → 'T Prints to a text writer, adding a newline. fprintf : TextWriter → TextWriterFormat<'T> → 'T Prints to a text writer.
- 6. Core.Printf Module bprintf : StringBuilder → BuilderFormat<'T> → 'T Prints to a StringBuilder. eprintf : TextWriterFormat<'T> → 'T Prints formatted output to stderr. eprintfn : TextWriterFormat<'T> → 'T Prints formatted output to stderr, adding a newline. fprintf : TextWriter → TextWriterFormat<'T> → 'T Prints to a text writer. fprintfn : TextWriter → TextWriterFormat<'T> → 'T Prints to a text writer, adding a newline.
- 7. Format Specifications • Used for formatting the input or output, • These are strings with % markers indicating format placeholders. • The syntax of a Format placeholders is − %[flags][width][.precision]type
- 8. Format Specifications printfn "d: %10d" 212 printfn “%010d” 212 Flag
- 9. Type Type Description %b Formats a bool, formatted as true or false. %c Formats a character. %s Formats a string, formatted as its contents, without interpreting any escape characters. %d, %i Formats any basic integer type formatted as a decimal integer, signed if the basic integer type is signed. %u Formats any basic integer type formatted as an unsigned decimal integer. %x Formats any basic integer type formatted as an unsigned hexadecimal integer, using lowercase letters a through f. %X Formats any basic integer type formatted as an unsigned hexadecimal integer, using uppercase letters A through F.
- 10. Type Type Description %o Formats any basic integer type formatted as an unsigned octal integer. %e, %E, %f, %F, %g, %G Formats any basic floating point type (float, float32) formatted using a C-style floating point format specifications. %e, %E Formats a signed value having the form [-]d.dddde[sign]ddd where d is a single decimal digit, dddd is one or more decimal digits, ddd is exactly three decimal digits, and sign is + or -. %f Formats a signed value having the form [-]dddd.dddd, where dddd is one or more decimal digits. The number of digits before the decimal point depends on the magnitude of the number, and the number of digits after the decimal point depends on the requested precision. %g, %G Formats a signed value printed in f or e format, whichever is more compact for the given value and precision. %M Formats a Decimal value. %O Formats any value, printed by boxing the object and using its ToString method. %A, %+A Formats any value, printed with the default layout settings. Use %+A to print the structure of discriminated unions with internal and private representations.
- 11. Width Value Description 0 Specifies to add zeros instead of spaces to make up the required width. - Specifies to left-justify the result within the width specified. + Specifies to add a + character if the number is positive (to match a - sign for negative numbers). ' ' (space) Specifies to add an extra space if the number is positive (to match a - sign for negative numbers). # Invalid. • The width is an optional parameter. • It is an integer that indicates the minimal width of the result. • For example, %5d prints an integer with at least spaces of 5 characters.
- 12. Width &Flag Flag Value Description 0 Specifies to add zeros instead of spaces to make up the required width. - Specifies to left-justify the result within the width specified. + Specifies to add a + character if the number is positive (to match a - sign for negative numbers). ' ' (space) Specifies to add an extra space if the number is positive (to match a - sign for negative numbers). # Invalid. • The width is an optional parameter. • It is an integer that indicates the minimal width of the result. • For example, %5d prints an integer with at least spaces of 5 characters.
- 13. Precision (optional) • Represents the number of digits after a floating point number. printf "%.2f" 12345.67890 O/P 12345.67 printf "%.7f" 12345.67890 O/P 12345.6789000
- 14. Read/Write Using Console Class • We can read and write to the console using the System.Console class 1. ReadLine 2. Write 3. WrileLine
- 15. Example open System let main() = Console.Write(“Enter your name: ") let name = Console.ReadLine() Console.Write("Hello,{0}", name) main()
- 16. Example:Date open System let main() = Console.WriteLine(System.String.Format("|{0:yy yy-MMM-dd}|", System.DateTime.Now)) main()
- 17. Method Read Reads the next character from the standard input stream. ReadKey() Obtains the next character or function key pressed by the user. The pressed key is displayed in the console window. Clear Clears the console buffer and corresponding console window
- 18. System.IO Namespace Files and Directories System.IO.File System.IO.Directory System.IO.Path System.IO.FileSystemWatcher
- 20. open System.IO type Data() = member x.Read() = // Read in a file with StreamReader. use stream = new StreamReader @"E:Fprogfile.txt" // Continue reading while valid lines. let mutable valid = true while (valid) do let line = stream.ReadLine() if (line = null) then valid <- false else // Display line. printfn "%A" line // Create instance of Data and Read in the file. let data = Data() data.Read() Reading from File And Display the content line by line Use: ensures the StreamReader is correctly disposed of when it is no longer needed.
- 21. • This is a simpler way to read all the lines in a file, but it may be less efficient on large files. • ReadAllLines returns an array of strings. • We use Seq.toList to get a list from the array. • And with Seq.where we get a sequence of only capitalized lines in the list. File.ReadAllLines
- 22. open System open System.IO let lines = File.ReadAllLines(@“E:Fprogfile.txt") // Convert file lines into a list. let list = Seq.toList lines printfn "%A" list // Get sequence of only capitalized lines in list. let uppercase = Seq.where (fun (n : String) -> Char.IsUpper(n, 0)) list printfn "%A" uppercase
- 23. ABC abc Cat Dog bird fish File.txt O/P ["ABC"; "abc"; "Cat"; "Dog"; "bird"; "fish"] seq ["ABC"; "Cat"; "Dog"]
- 24. open System.IO // Name spaces can be opened just as modules File.WriteAllText("test.txt", "Hello Theren Welcome All”) let msg = File.ReadAllText("test.txt") printfn "%s" msg Creates a file called test.txt, writes a message there, reads the text from the file and prints it on the console.
- 25. Delegates in F# • A special function that encapsulate a method and represents a method signature. • Similar to pointers to functions in C or C++. • A reference type variable that holds the address of functions. • The reference can be changed at runtime. • Used for implementing events and call-back functions.
- 26. Delegates in F# • A delegate is referred to as type-safe function pointers, • If the method with two int parameters and a return type is an int then the delegate that you are declaring should also have the same signature. • That is why a delegate is referred to as type-safe function.
- 27. 3 ways to define Delegates Methods Declaration Instantiation Invocation
- 28. Types of Delegates Delegates Types Simple Delegate Multicast Delegate
- 29. Delegates in F# :Syntax type delegate-typename = delegate of type1 -> type2 // Delegate1 works with tuple arguments. type Delegate1 = delegate of (int * int) -> int // Delegate2 works with curried arguments. type Delegate2 = delegate of int * int -> int Syntax Both the delegates can be used to reference any method that has two int parameters and returns an int type variable. argument type(s). return type.
- 30. Point to Remember • Delegates can be attached to function values, and static or instance methods. • F# function values can be passed directly as arguments to delegate constructors. • For a static method the delegate is called by using the name of the class and the method. • For an instance method, the name of the object instance and method is used.
- 31. Point to Remember • The Invoke method on the delegate type calls the encapsulated function. • Also, delegates can be passed as function values by referencing the Invoke method name without the parentheses.
- 32. Example: Implementation of Add & Sub operation using Delegates 1. Define two types of Methods : Static & Instance 2. Define Delegates 3. Invoke delegates 4. Calling static method using delegates 5. Calling Instance method using delegates 6. Calling Delegates
- 33. Method Defining-Static & Instance type Test1() = static member add(a : int, b : int) = a + b static member sub(a : int) (b : int) = a - b member x.Add(a : int, b : int) = a + b member x.Sub(a : int) (b : int) = a - b
- 34. Defining Delegates // Delegate1 works with tuple arguments. type Delegate1 = delegate of (int * int) -> int // Delegate2 works with curried arguments. type Delegate2 = delegate of int * int -> int
- 35. Invoking Delegates let InvokeDelegate1 (dlg : Delegate1) (a : int) (b: int) = dlg.Invoke(a, b) let InvokeDelegate2 (dlg : Delegate2) (a : int) (b: int) = dlg.Invoke(a, b)
- 36. Calling static Method // For static methods, use the class name, the dot operator, and the name of the static method. let del1 : Delegate1 = new Delegate1( Test1.add ) let del2 : Delegate2 = new Delegate2( Test1.sub )
- 37. For Instance Method // For instance methods, use the instance value name, the dot operator, and the instance method name. let testObject = Test1() let del3 : Delegate1 = new Delegate1( testObject.Add ) let del4 : Delegate2 = new Delegate2( testObject.Sub )
- 38. Calling Delegates for (a, b) in [ (100, 200); (10, 20) ] do printfn "%d + %d = %d" a b (InvokeDelegate1 del1 a b) printfn "%d - %d = %d" a b (InvokeDelegate2 del2 a b) printfn "%d + %d = %d" a b (InvokeDelegate1 del3 a b) printfn "%d - %d = %d" a b (InvokeDelegate2 del4 a b)