Functions and Function Literals 1 28 2011 Opening Discussion Minute 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 More How 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 Math Let 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 Programming The 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 Scala We declare functions in Scala using def Here is the general form def name arg1 Type1 arg2 Type2 Type expression The 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 Decomposition Never 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 down This is the normal approach where you start with the full problem and break it into pieces Bottom up Sometimes you realize that different trivial pieces will be useful and build up from those Function Literals Just 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 b Types don t have to be specified in many situations only if Scala can t figure it out Minute Essay Do 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 concepts
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