Scala Expressions and Types 1 19 2011 Opening Discussion Command line impressions Powerful but difficult More confusing than a GUI for copying and moving Similarities to Matlab Remembering memorizing commands What happens if someone restarts a computer you are sshed into Saving terminal sessions Solutions to the IcP Text Files Editors Programs are typically written as plain text files and should be edited with a text editor Notepad is a basic text editor on Windows Word is NOT a text editor Some text editors are better than others for programming In this class we will use vi vi The vi editor is standard on Linux which is one reason we like to use it It is also good for programming Has modes Start in command mode You type in an edit mode i insert I insert at beginning of line a append A append at end of line R replace characters Other Commands x delete characters dd delete lines yy yank copy lines p or P paste before or after r replace a single character J join lines and n search for something and next cw change a word repeat last command u and Crtl r Undo and redo Scala Script First Program Let s go into your course and use vi to write our first Scala program then run it The standard first program is Hello World and I don t want to break with tradition Scala REPL If you just type scala and don t provide a file name to run it will drop you into the REPL Read Evaluate Print Loop Here you can enter individual commands and have them run It is great for testing things out and getting to learn the language Key Terms Token A set of characters that has meaning to the language Statement A set of tokens that give a complete instruction Expression Tokens put together that produce a value Type All values have types A type is a set of values and the operations allowed on them Literal A token that represents a value Numeric String Character Boolean Statements and Semicolon Inference In Scala as with most programming languages programs are made by putting together statements In Scala any expression is a valid statement as are a few other constructs Statements end with semicolons but they will be inferred at the end of a line if they make sense so you rarely type them Operators We can build longer expressions by putting literals together with operators Let s start off by playing with some of the numeric operations you are probably familiar with You can get the remainder after division with Objects An object is defined to be information along with the things you can do with that information The information in an object is called the properties The actions are called methods In Scala even things like Int are objects and have methods on them Methods The normal way to call a method in Scala and most other object oriented languages is to put a period after the object and follow it with the method name The REPL will do tab completion and list methods for you Let s look at the methods on some basic types and try calling them Arguments Some methods need additional information to work To give this to the method we pass in arguments Arguments are put in parentheses and separated by commas if there is more than one The parentheses are generally optional in Scala if there is no argument Operator Syntax All the operators in Scala are really just methods Scala allows any method with zero or one arguments to be called with an operator syntax That means you leave off the dot and the parentheses If a method takes no arguments you can call it without the dot Minute Essay What in today s lectures was confusing Was there anything that surprised you
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