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Like most languages, Python has ways of storing groups of objects, which is fortunate because a game with only one alien, one bullet, or one weapon would be quite dull! Python objects that store other objects are known as collections, and one of the simplest and most often used collection is the list. Let s start by creating an empty list: >>> my_list=[] The square brackets create an empty list, which is then assigned to the variable my_list. To add something to a list you can use the append method, which tacks any Python object you give it onto the end. Let s pretend our list is going to hold our shopping for the week, and add a couple of items: >>> my_list.append('chopsticks') >>> my_list.append('soy sauce') Here we have added two strings to my_list, but we could just as easily have added any other of Python s objects, including other lists. If you now type my_list at the Python prompt, it will display the contents of it for you: >>> my_list ['chopsticks', 'soy sauce'] Here we can see that the two strings are now stored inside the list. We cannot live on chopsticks and soy sauce alone, so let s add a few more items to our shopping list: >>> my_list.append('wasabi') >>> my_list.append('fugu') >>> my_list.append('sake') >>> my_list.append('apple pie') >>> my_list ['chopsticks', 'soy sauce', 'wasabi', 'fugu', 'sake', 'apple pie']

In this chapter, you looked at the main features and techniques for language-oriented programming in F#. You have seen various techniques; some use data structures as little languages or work with quotations, which involve working with the existing F# syntax to change or extend it. Others, such as implementing a parser, enable you to work with just about any language that is text-based, whether this language is of your own design (or perhaps more commonly) a preexisting language. All these techniques can lead to big productivity gains if you use them correctly. The next chapter will look at how to parse text using F#. This will allow you to create languages that are not embedded within F#, yet will allow you to work with the main text-based formats that are defined.

For the Display Order History story, the result should be a page that displays a customer s complete history of orders. The developers can immediately recognize four tasks necessary to complete this story: adding a My Account button to a customer s top navigation bar, creating a My Account page with a left-side navigation bar with an Order History link, retrieving all of the customer s previous orders, and displaying those orders. Figure 14-3 shows these tasks.

here are a variety of ways that the player can interact with a game, and this chapter covers the various input devices in detail. In addition to retrieving information from the devices, we will also explore how to translate what the player does into meaningful events in the game. This is extremely important for any game regardless of how good a game looks and sounds, it must also be easy to interact with.

Structured text formats that are readable by both humans and machines have been popular almost since the beginning of computing. Programming languages are a good example of this, but there are many others. Parsing text is related to the previous chapter, language orient programming, because if you want to implement a language that is not embedded in F# then creating a parser for that format would be the first step. However, there are many reasons that you may want to parse an existing text format, so I did not want to limit this chapter to parsing languages. Simple text formats such as comma separated values (CSV) are generally quite straightforward to parse, although even CVS can have its challenges, like handling escape characters correctly. As languages become more complicated, parsing them becomes more challenging. Even apparently simple languages like HTML can present some challenges when parsing. To a certain extent this has driven the popularity of XML, because parsers as prepackaged software components remove a lot of the work of parsing XML. Due to some of the limitations of XML other text formats that do require parsers to be written are still popular. The renewed interest in domain specific languages has led to a renewed interest in parsing text, so new DSLs that are external to programming languages can be created. Fortunately, F# comes with several different tools for parsing text. In this chapter, you ll examine two of them: using fslex.exe & fsyacc.exe using the open source library FParsec As these two examples relate to parsing languages, I ll start off with an example of how you might parse a simple CSV format.