Useful Services from the System Namespace in Font

Creator PDF417 in Font Useful Services from the System Namespace

Contains functions to convert numeric representations to and from bit representations Contains functions to convert between various numeric representations Contains constants and static methods for trigonometric, logarithmic, and other common mathematical functions Provides objects to act as random number generators Provides objects implementing various types of comparisons on strings (case insensitive, and so on)

In 3 you saw the different forms of string literals (strings with escape characters, verbatim strings, and byte arrays) and the most typical operations such as concatenation using string builders. You may also remember that string values are immutable and that string operations that change their input return a new string that represents the result. In the following sections, we cover further ways to work with strings and text.

One of the most popular ways of working with strings as data is through the use of regular expressions. This is done using the functionality from the .NET System.Text.RegularExpressions namespace. To get started, first note that the F# library includes the following definition: open System.Text.RegularExpressions let regex s = new Regex(s) To this you can add the following Perl-like operators: let (=~) s (re:Regex) = re.IsMatch(s) let (<>~) s (re:Regex) = not (s =~ re) Here the inferred types are as follows: val regex : string -> Regex val ( =~ ) : string -> Regex -> bool val ( <>~ ) : string -> Regex -> bool The infix operators allow you to test for matches: > let samplestring = "This is a string";; val samplestring : string > if samplestring =~ regex "his" then printfn "A Match! ";; A Match! val it : unit = () Regular expressions can include *, +, and symbols for zero or more occurrences, one or more occurrences, and zero or one occurrences of the immediately preceding regular expression and can include parentheses to group regular expressions. For example: > "This is a string" =~ regex "(is )+";; val it : bool = true

Regular expressions can also be used to split strings: > (regex " ").Split("This is a string");; val it : string [] = [|"This"; "is"; "a"; "string"|] Here we have used the regular expression " " for whitespace. In reality, you probably want to use the regular expression " +" to match multiple spaces. Better still, you can match any Unicode whitespace character using \s, including end-of-line markers; however, when using escape characters, you will want to use verbatim strings to specify the regular expression, such as @"\s+". We discussed verbatim strings in 3. Let s try this: > (regex @"\s+").Split("I'm a little teapot");; val it : string [] = [|"I'm"; "a"; "little"; "teapot"|] > (regex @"\s+").Split("I'm a little \t\t\n\t\n\t teapot");; val it : string [] = [|"I'm"; "a"; "little"; "teapot"|] Here s how to match by using the method Match instead of using =~ and IsMatch. This lets you examine the positions of a match. > let m = (regex @"joe").Match("maryjoewashere");; val m : Match > if m.Success then printfn "Matched at position %d" m.Index;; Matched at position 4 val it : unit = () Replacing text is also easy: > let text = "was a dark and stormy night";; val text: string > let t2 = (regex @"\w+").Replace(text, "WORD");; val t2: string > t2;; val it : string = "WORD WORD WORD WORD WORD WORD" Here we ve used the regular expression "\w+" for a sequence of word characters.

Characters other than . $ ^ { [ ( | ) * + \ match themselves. Matches any character, except \n. If RegexOptions.SingleLine is specified, then it matches every character. Matches any of the given characters or character ranges. Any character other than the given characters of character ranges. Matches any character in the named character class specified by {name}. See the .NET documentation for full details. Matches text not included in groups and block ranges specified in {name}. Matches any word character. Matches any nonword character. Matches any whitespace character. Matches any nonwhitespace character. Matches any decimal digit. Matches any nondigit. Matches a bell (alarm) \u0007. Matches a backspace \u0008 if in a [] character class; otherwise, in a regular expression, \b denotes a word boundary (between \w and \W characters). In a replacement pattern, \b always denotes a backspace. Matches a tab \u0009. Matches a carriage return \u000D. Matches a vertical tab \u000B. Matches a form feed \u000C. Matches a new line \u000A. Matches an escape \u001B. Matches a back reference. Matches an ASCII character as octal. Matches an ASCII character using hexadecimal representation (exactly two digits). Matches an ASCII control character; for example, \cC is Ctrl+C. Matches a Unicode character using hexadecimal representation (exactly four digits). When followed by a character that is not recognized as an escaped character, matches that character. For example, \* is the same as \x2A.

\t \r \v \f \n \e \digit \040 \x20 \cC \u0020 \