Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Functions and Function Literals1-28-2011Opening DiscussionMinute Essays:Getting rid of vi search highlighting.Do I have any pets?What is the point of having var?Lifetime of REPL variables?Correcting the wage formatting.New terminals without the mouse.Reason for plus in “+word+”.What is Scala reading for 1.0-0.9?MoreHow do we write code to use outside the terminal?Finding in-class code.Importance of Boolean.Spurs chances and respect.ACM and Major's e-mail list.Functions in MathLet's review the concept of functions from math.In algebra a function would take one or more values and give you back a value. The values were generally numbers.In higher level math this is generalized with things like sets.In math functions the same input leads to the same result.Functions in ProgrammingThe concept of a function is critically important to programming.Functions can take one or more arguments and give us back values. (Most languages allow only one return value.)Let's think of some examples of functions that we could write.Functions in ScalaWe declare functions in Scala using def. Here is the general form.def name(ar g1:Type1, arg2:Type2, ...):Type = expressionThe argument list can have zero or more elements. If there are zero even the parentheses can be left off.Function arguments must have types.The return type is optional, but it is recommended.Why Functions?Functions are used in programs for a number of reasons.Reduce code duplication. You can call the same function multiple times and only write it once.Improve readability and maintainability. Good function names make it easier to read. Small functions are easier to test and debug.Break problems down/problem decomposition.Problem DecompositionNever solve a hard problem. If a problem is hard, break it into smaller problems that are easier. Repeat until you are only solving trivial problems.Top-downThis is the “normal” approach where you start with the full problem and break it into pieces.Bottom-upSometimes you realize that different trivial pieces will be useful and build up from those.Function LiteralsJust like 5 is a literal for an Int and “hi” is a literal for a string, you can write literals of functions.The full syntax is an argument list followed by an equals arrow followed by the function expression.(a:Int,b:Int) => 3*a+2*bTypes don't have to be specified in many situations, only if Scala can't figure it out.Minute EssayDo you have any questions about functions?We will look at solutions to IcP #2 on Monday.The reading is highly recommended to help you truly understand
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