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#blognavi これも忘れないうちに Choosing Sides Comics and Politics - 11/21/2006 - Publishers Weekly Suspension of Disbelief I just can't take the SRA seriously 参考 Cease Fire In Marvel's Civil War - 8/22/2006 - Publishers Weekly Comic Book Politics カテゴリ [メモ] - trackback- 2007年01月18日 23 06 10 #blognavi
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このページはhttp //martinfowler.com/dslwip/Intro.htmlからの引用です | DSL-WIP Home | WORK-IN-PROGRESS - this material is still under development An Introductory Example Last significant update 06 Aug 07 Contents Miss Grant s Controller The State Machine Model Programming the Controller with a Domain Specific Language Languages and Model Using Code-Generation Using Language Workbenches Visualization Picking up this book, you may be asking yourself such questions as what is a DSL , how does it fit in with my usual development work and why would I find such a thing useful ? This chapter begins by looking at these questions. I ll talk about what a DSL is, the various types of DSL, the reasons to use a DSL, and the broader topic of language processing. At this stage I won t talk about how the various styles of DSL work - we ll get into that later. Miss Grant s Controller As is usual for me, I ll base this discussion on an example, as I find that a concrete example usually makes it easier to follow an abstract topic like this. Let s imagine a company that makes systems to control access to secret compartments. Their customers are people who are bored with numeric keypads and security codes, instead preferring something recalling bad movies set in gothic castles. So Miss Grant has a secret compartment in her bedroom that is normally locked and concealed. To open it she has to close the door, open the second draw in her chest, turn her bedside light on - and then the secret panel is unlocked for her to open. Mr G has the same basic system for a panel in his bedroom. He has to open his bathroom door and turn on the main light which allows him to open the panel. The panel reveals a safe, but it has an overriding lock that cannot be opened unless he turns his light off and on again. Mr C has a compartment in his office, he has to close his main door, take a picture off the wall, turn his desklight on three times, open the top draw of his filing cabinet, turn the desklight off - and then the panel s unlocked. If he forgets to turn the desklight off, he wants an alarm to sound. Although this example is deliberately whimsical, the underlying point isn t that unusual. What we have is a family of systems which share most components and behaviors, but have some important differences. In this case we have some kind of controller software which communicates with various devices around the room. The variability is in the sequence of actions that can be carried out and the actions that the software does as a result of these sequences. We want to arrange things so that the company can install a new system with the minimum of effort, so it must be easy for them to program the sequence of actions into the controller. Looking at their many customers they realize there is a common theme to the way they behave. The various devices send events as they are manipulated. The system reacts differently to events depending on the recent sequence of events. This style of thinking about behavior is that of a state machine. Thus it makes sense to build a model of a state machine that can be programmed for individual customers at each site. That way the general behavior can be resued for each customer and setting up a new customer just means writing the specific things for each case. The software is written in java, running on a job lot of toasters they picked up from a failed dot com. The State Machine Model There are many varieties of state machine models around, this one is simple, and with a little twist for the this particular case. There are frameworks out there to run state machines, but we can do with something much simpler that s more suited to this particular domain. By doing this we give up some power for an easier job working with it. This issue isn t really part of the DSL discussion so I won t explore it further. To help understand how the state machine model works, let s take Miss Grant s system. Figure 1 State diagram for Miss Grant The system has a controller that receives events and commands from the various devices scattered around. Each event and command has a four letter code that s the actual signal sent through the communication channels. I want to refer to these in the controller code with symbolic names, so I create event and command classes with a code and a name. I keep them as separate classes (with a superclass) as they play different roles in the controller code. class AbstractEvent... private String name, code; public AbstractEvent(String name, String code) { this.name = name; this.code = code; } public String getCode() { return code;} public String getName() { return name;} public class Command extends AbstractEvent public class Event extends AbstractEvent Figure 2 Class diagram of the state machine framework [TBD Add reset event association to class diagram] The key to the structure is that state class. Each state class keeps track of the events and commands. class State... private String name; private List Command actions = new ArrayList Command (); private Map String, Transition transitions = new HashMap String, Transition (); public void addTransition(Event event, State targetState) { transitions.put(event.getCode(), new Transition(this, event, targetState)); } class Transition... private final State source, target; private final Event trigger; public Transition(State source, Event trigger, State target) { this.source = source; this.target = target; this.trigger = trigger; } public State getSource() {return source;} public State getTarget() {return target;} public Event getTrigger() {return trigger;} public String getEventCode() {return trigger.getCode();} The state machine holds on to its start state. class StateMachine... private State start; public StateMachine(State start) { this.start = start; } Any other states in the machine are then those that are reachable from this state. class StateMachine... public Collection State getStates() { List State result = new ArrayList State (); gatherForwards(result, start); return result; } private void gatherForwards(Collection State result, State start) { if (start == null) return; if (result.contains(start)) return; else { result.add(start); for (State next start.getAllTargets()) { gatherForwards(result, next); } return; } } class State... Collection State getAllTargets() { List State result = new ArrayList State (); for (Transition t transitions.values()) result.add(t.getTarget()); return result; } There is one particular wrinkle to this problem. These controllers have a particular nature to them in that most of the time they are in their start state, which is effectively an idle state. There are events that advance the state machine, and there are events that take you back to that start state. For this case opening the door always takes you back to the start. So I let the machine keep track of reset events. class StateMachine... private List Event resetEvents = new ArrayList Event (); public void addResetEvents(Event... events) { for (Event e events) resetEvents.add(e); } I don t need to have a separate structure for reset events here. I could handle this by simply declaring extra transitions on the state machine like this class StateMachine... private void addResetEvent_byAddingTransitions(Event e) { for (State s getStates()) if (!s.hasTransition(e.getCode())) s.addTransition(e, start); } I prefer explicit reset events on the machine becuase that better expresses the intention of what I m trying to do. While it does complicate the machine a bit, it keeps the clarity of my intention of how a general machine is supposed to work, as well as keeping the intention of how a particular machine is defined. With the structure out of the way, now lets move on to the behavior. As it turns out, it s really quite simple. The controller has a handle method that takes the event code it receives from the device. class Controller... private State currentState; private StateMachine machine; public CommandChannel getCommandChannel() { return commandsChannel; } protected CommandChannel commandsChannel; public void handle(String eventCode) { if (currentState.hasTransition(eventCode)) transitionTo(currentState.targetState(eventCode)); else if (machine.isResetEvent(eventCode)) transitionTo(machine.getStart()); // ignore unknown events } private void transitionTo(State target) { currentState = target; currentState.executeActions(commandsChannel); } class State... public boolean hasTransition(String eventCode) { return transitions.containsKey(eventCode); } public State targetState(String eventCode) { return transitions.get(eventCode).getTarget(); } public void executeActions(CommandChannel commandsChannel) { for (Command c actions) commandsChannel.send(c.getCode()); } class StateMachine... public boolean isResetEvent(String eventCode) { return resetEventCodes().contains(eventCode); } private List String resetEventCodes() { List String result = new ArrayList String (); for (Event e resetEvents) result.add(e.getCode()); return result; } It ignores any events that are not registered on the state. For any events that are recognized, it transitions to the target state and executes any commands defined on that target state. Programming the Controller with a Domain Specific Language Now I ve implemented the state machine model, I can now program Miss Grant s controller like this. Event doorClosed = new Event( doorClosed , D1CL ); Event drawOpened = new Event( drawOpened , D2OP ); Event lightOn = new Event( lightOn , L1ON ); Event doorOpened = new Event( doorOpened , D1OP ); Event panelClosed = new Event( panelClosed , PNCL ); Command unlockPanelCmd = new Command( unlockPanel , PNUL ); Command lockPanelCmd = new Command( lockPanel , PNLK ); Command lockDoorCmd = new Command( lockDoor , D1LK ); Command unlockDoorCmd = new Command( unlockDoor , D1UL ); State idle = new State( idle ); State activeState = new State( active ); State waitingForLightState = new State( waitingForLight ); State waitingForDrawState = new State( waitingForDraw ); State unlockedPanelState = new State( unlockedPanel ); StateMachine machine = new StateMachine(idle); idle.addTransition(doorClosed, activeState); idle.addAction(unlockDoorCmd); idle.addAction(lockPanelCmd); activeState.addTransition(drawOpened, waitingForLightState); activeState.addTransition(lightOn, waitingForDrawState); waitingForLightState.addTransition(lightOn, unlockedPanelState); waitingForDrawState.addTransition(drawOpened, unlockedPanelState); unlockedPanelState.addAction(unlockPanelCmd); unlockedPanelState.addAction(lockDoorCmd); unlockedPanelState.addTransition(panelClosed, idle); machine.addResetEvents(doorOpened); I look at this last bit of code as quite different in nature to the previous peices. The earlier code described how to build the state machine model, this last bit of code is about how to configure that model for one particular controller. You often see divisions like this. On the one hand is library, framework, or component implementation code; on the other is configuration or component assembly code. Essentially it is the separation of common code from variable code. We structure the common code in a set of components that we then configure for different purposes. Here is another way of representing that configuration code. stateMachine start = idle event name= doorClosed code= D1CL / event name= drawOpened code= D2OP / event name= lightOn code= L1ON / event name= doorOpened code= D1OP / event name= panelClosed code= PNCL / command name= unlockPanel code= PNUL / command name= lockPanel code= PNLK / command name= lockDoor code= D1LK / command name= unlockDoor code= D1UL / state name= idle transition event= doorClosed target= active / action command= unlockDoor / action command= lockPanel / /state state name= active transition event= drawOpened target= waitingForLight / transition event= lightOn target= waitingForDraw / /state state name= waitingForLight transition event= lightOn target= unlockedPanel / /state state name= waitingForDraw transition event= drawOpened target= unlockedPanel / /state state name= unlockedPanel action command= unlockPanel / action command= lockDoor / transition event= panelClosed target= idle / /state resetEvent name = doorOpened / /stateMachine This style of representation should look familiar to most readers, I ve expressed it as an XML file. There are several advantages to doing it this way. One obvious reason is that now we don t have to compile a separate java program for each controller we put into the field - instead we can just compile the state machine components plus an appropritate parser into a common jar, and ship the xml file to be read when the machine starts up. Any changes to the behavior of the controller can be done without having to distribute a new jar. (We do, of course, pay for this in that any mistakes in the syntax of the configuration can only be detected at run time.) A second advantage is in the expressiveness of the file itself. We no longer need to worry about the details of making the various connections through variables. Instead we have a more declarative approach that in many ways reads much more clearly. We re also limited in that we can only express configuration in this file - limitations like this often are helpful because they can reduce the chances for people making mistakes in the component assembly code. These advantages are why so many frameworks in Java and C# are configured with XML configuration files. These days it sometimes feels that you re doing more programming with XML than you are with main programming language. Here s another version of the configuration code. events doorClosed D1CL drawOpened D2OP lightOn L1ON doorOpened D1OP panelClosed PNCL end resetEvents doorOpened end commands unlockPanel PNUL lockPanel PNLK lockDoor D1LK unlockDoor D1UL end state idle actions {unlockDoor lockPanel} doorClosed = active end state active drawOpened = waitingForLight lightOn = waitingForDraw end state waitingForLight lightOn = unlockedPanel end state waitingForDraw drawOpened = unlockedPanel end state unlockedPanel actions {unlockPanel lockDoor} panelClosed = idle end This is code, although not in a syntax that s familiar to you. In fact it s a custom syntax that I made up for this example. I think it s a syntax that s easier to write, and above all easier to read, than the XML syntax. It s terser and avoids a lot of the quoting and noise characters that the XML suffers from. You probably wouldn t have done it exactly the same way, but the point is that you can construct whatever syntax you and your team prefers. You can still load it in at runtime (like the XML) but you don t have to (as you don t with the XML) if you want it at compile time. This language is a Domain Specific Language, and shares many of the characteristics of DSLs. Firstly it s suitable only for a very narrow purpose - it can t do anything other than configure this particular kind of state machine. As a result the DSL is very simple - there s no facility for control structures or anything else. It s not even Turing complete. You couldn t write a whole application in this language - all you can do is describe one small aspect of an application. As a result the DSL has to be combined with other languages to get anything done. But the simplicity of the DSL means it s easy to edit and process. Now look again at the XML representation. Is this a DSL? I would argue that it is. It s wrapped in an XML carrier syntax - but it s still a DSL. This example thus raises a design issue - is it better to have custom syntax for a DSL or an XML syntax? The XML syntax can be easier to parse since people are so familiar with parsing XML. (As it happened for this example it took me the about the same amount of time to write the parser for the custom syntax as it did for the XML.) I d contend that the custom syntax is much easier to read, at least in this case. But however you view this choice the core trade-offs around DSLs are the same. Indeed you can argue that most XML configuration files are essentially DSLs. Let s go back a step further, back to the configuration code in Java I showed you earlier - is that a DSL? While you re thinking about that question look at this code. Does this look like a DSL for this problem? event doorClosed, D1CL event drawOpened, D2OP event lightOn, L1ON event doorOpened, D1OP event panelClosed, PNCL command unlockPanel, PNUL command lockPanel, PNLK command lockDoor, D1LK command unlockDoor, D1UL resetEvents doorOpened state idle do actions unlockDoor, lockPanel transitions doorClosed = active end state active do transitions drawOpened = waitingForLight, lightOn = waitingForDraw end state waitingForLight do transitions lightOn = unlockedPanel end state waitingForDraw do transitions drawOpened = unlockedPanel end state unlockedPanel do actions unlockPanel, lockDoor transitions panelClosed = idle end It s a bit noisier than the custom language earlier, but still pretty clear. Readers who have similar language likings to me will probably know that it s Ruby. Ruby gives me a lot of syntactic options that makes for more readable code, so I can make it look very similar to the custom language. Ruby developers would consider this code to be a DSL. I use a subset of the capabilities of Ruby and capture same ideas as our XML and custom syntax. Essentially I m embedding the DSL into ruby, using a subset of ruby as my syntax. To an extent this is more a matter of attitude than of anything else. I m choosing to look at the Ruby code through DSL glasses. But it s a point of view with a long tradition - Lisp programmers often think of creating DSLs inside Lisp. This brings me to pointing out that there are two kinds of textual DSLs which I call external and internal DSLs. AnExternal DSLis a domain specific language represented in a separate language to the main programming language it s working with. This language may be a custom syntax, or it may follow the syntax of another representation (like XML). AnInternal DSLis DSL expressed within the syntax of a general purpose language. It s a stylized use of that language for a domain specific purpose. You may also hear the termembedded DSLas a synonym for internal DSL. Although it is fairly widely used, I avoid this term because you also hear embedded language applied to scripting languages embedded within applications such as VBA in Excel or Scheme in the Gimp. So I use internal DSL to avoid confusion. Now think again about the original java configuration code - is this a DSL? I would argue that it isn t. That code feels like stitching together with an API, while the ruby code above has more the feel of a declarative language. Does this mean you can t do an internal DSL in Java? How about this? public class BasicStateMachine extends StateMachineBuilder { Events doorClosed, drawOpened, lightOn, panelClosed; Commands unlockPanel, lockPanel, lockDoor, unlockDoor; States idle, active, waitingForLight, waitingForDraw, unlockedPanel; ResetEvents doorOpened; protected void defineStateMachine() { doorClosed. code( D1CL ); drawOpened. code( D2OP ); lightOn. code( L1ON ); panelClosed.code( PNCL ); doorOpened. code( D1OP ); unlockPanel.code( PNUL ); lockPanel. code( PNLK ); lockDoor. code( D1LK ); unlockDoor. code( D1UL ); idle .actions(unlockDoor, lockPanel) .transition(doorClosed).to(active) ; active .transition(drawOpened).to(waitingForLight) .transition(lightOn). to(waitingForDraw) ; waitingForLight .transition(lightOn).to(unlockedPanel) ; waitingForDraw .transition(drawOpened).to(unlockedPanel) ; unlockedPanel .actions(unlockPanel, lockDoor) .transition(panelClosed).to(idle) ; } } It s formatted oddly, and uses some unusual programming conventions, but it is valid Java. It s java written in what is these days called a Fluent Interface style. AFluent Interfaceis an API that s designed to read like an internal DSL. This I would call a DSL - although it s more messy than the ruby DSL it still has that declarative flow that a DSL needs. What makes a fluent interface different to a normal API? This is a tough question that I ll spend more time onlater), but it comes down to a rather fuzzy notion of a language-like flow. Given this distinction it s useful to have a name for a non-fluent API - I ll use the termcommand-query API. Languages and Model There s an important inter-relationship here between the various DSLs and the underlying state-machine model. To implement each of these languages I wrote code that translated from expressions in the DSL into calls on the command-query interface of the model. So while I was parsing the custom syntax version and came across commands unlockPanel PNUL I would create a new command object (new Command( unlockPanel , PNUL )) and keep it to one side (in aSymbol Table) so that when I sawactions {unlockPanelI could add it to the appropriate state (usingaddAction). As a result each DSL I ve shown you created the same configuration of objects in the model. The model, as I discussed earlier, is the engine that provides the behavior of the state-machine. So once we have a populated model, we have a running program whose behavior is encoded in the inter-relationships between the objects in that model. This style is often called an Active Object Model, because in order to understand the behavior of the state machine you can t just look at the code, you also have to look at the way object instances are wired together. Of course this is always true to some extent, any program gives different results with different data, but there is a sense of a greater difference here as the presence of the state objects alters the behavior of the system to a significantly greater degree. When people discuss a programming language you often hear them talk about syntax and semantics. The syntax captures the legal expressions of the program, what in the custom syntax DSL is captured by the grammar. The semantics of a program is what it means, that is what it does when it executes. In this case it is the model that defines those semantics - which is why I will refer to it as aSemantic Model. In this example theSemantic Modelis an object model. ASemantic Modelcan also take other forms. It can be a pure data structure with all behavior in separate functions. I would still refer to it as an active model, because the data structure defines the program s behavior. Looking at it from this point of view, the DSL merely acts as a mechanism for expressing how the model is configured. I often refer to a DSL as a thin facade over a framework. Much of the benefits of using this approach comes from the model rather than the DSLs. The fact that I can easily configure a new state machine for a customer is a property of the model, not the DSL. The fact that I can make a change to a controller at run-time, without compiling, is a feature of the model, not the DSL. The fact I m reusing code across multiple installations of controllers is a property of the model, not the DSL. A model provides many benefits without any DSLs present. As a result we use them all the time. We use libraries and frameworks to wisely avoid work. In our own software we construct our own models, building up abstractions that allow us to program faster. Good models, whether published as libraries and frameworks or just serving our own code, can work just fine without any DSL in sight. But DSLs can enhance the the capabilities of a model. The right DSL makes it easier to understand what a particular state machine does. Some DSLs allow you to configure the model at run time. DSLs are thus a useful adjunct to some models. In discussing this example I described a circumstance where the model was built first, and then I layered a DSL over the model to help manipulate it. I described it that way becuase I think that s an easy way to understand how DSLs fit into software development. Although the model-first case is a common one, it isn t the only one. In a different scenario you talk with the domain experts and posit that a state machine approach is something they understand. You then work with the domain experts to create a DSL that they can understand. In this case you build the DSL and model simultaneously. Using Code-Generation In my discussion so far, I process the DSL by populating theSemantic Modeland then execute theSemantic Modelto provide the behavior that I want from the controller. This approach is what s known in language circles as interpretation. When weinterpretsome text, we parse it and immediately produce the result that we want from the program. (Interpret is a tricky word in software circles, since it carries all sorts of connotations for people, however I ll use it strictly to mean this form of immediate execution.) In the language world, the alternative to interpretation is compilation. Withcompilation, we parse some program text and produce an intermediate output, which is then separately processed to provide the behavior we desire. In the context of DSLs the compilation approach is usually referred to ascode-generation. In this case this might mean generating some java code to represent the particular behavior of Miss Grant s controller. Code generation is often awkward in that it often pushes you to an extra compilation. To build your program you have to first compile the state framework and the parser, then run the parser to generate the source code for Miss Grant s controller, then compile that generated code. This makes your build process much more complicated. However an advantage of code generation is that there s no reason why you have to generate code in same programming language that you use for the parser. In this case you can avoid the second compilation step by generating code for a dynamic language such as javascript or jruby. Code generation is also useful when you want to use DSLs with a language platform that doesn t have the tools for DSL support. I ve come across recent projects that generate code for MathCAD, SQL, and COBOL. Many writings on DSLs focus on code-generation, even to the point of making code-generation the primary aim of the exercise. As a result you can find articles and books extolling the virtues of code-generation. In my view, however, code-generation is merely an implementation mechanism, one that isn t actually needed in most cases. Certainly there are plenty of times when you must use code-generation, but there are even more plenty of times when you don t need it. Using code-generation is one case where many people don t use aSemantic Model. In this case you parse the input text and directly produce the generated code. Although this is a common way of working with code-generated DSLs, it isn t one I reccommend for any but the very simplest cases. Using aSemantic Modelallows me to separate the parsing, the execution semantics, and the code generation into separate problems. This separation makes the whole exercise a lot simpler. It also allows me to change my mind. I can change my DSL from an internal to an external DSL (say) without altering my code-generation routines. Similarly I can easily generate multiple outputs without complicating my parse. I can also use both an interpreted model and code generation off the sameSemantic Model. As a result for almost all of this book, I m going to assume aSemantic Modelis present and the centre of the DSL effort. Using Language Workbenches The two styles of DSL I ve shown so far (internal and external) are the traditional ways of thinking about DSLs. They may not be as widely understood and used as they should be, but they have a long history and moderately wide usage. As a result the rest of this book concentrates on getting you started with these approaches using tools that are mature and easy to obtain. But there is a whole new category of tools on the horizon that could change the game of DSLs significantly tools I call Language Workbenches. ALanguage Workbenchis tool designed to help people create new DSLs, together with high quality tooling required to use those DSLs effectively. One of the big disadvantages of using an external DSL is that you re stuck with relatively limited tooling. Setting up syntax highlighting with a text editor is about as far as most people go. While you can argue that the simplicity of a DSL and the small size of the scripts means that may be enough, there s also an argument for the kind of sophisticated tooling that modern post-IntelliJ IDEs support. Language Workbenches make it easy not just to define a parser, but also to define a custom editing environment for that language. All of this is valuable, but the truly interesting aspect of language workbenches is that they allow a DSL designer to go beyond the the traditional text-based source editing, to different forms of language. The most obvious example of this is support for diagrammatic languages, which would allow me to specify the secret panel state machine directly with a state transition diagram. Figure 3 The secret panel state machine displayed in the MetaEdit language workbench.(source MetaCase) Not just does a tool like this allow you to have diagrammtic languages, it also allows you to look at a DSL script from multiple perspectives. In Figure3there is a diagram, but also lists of states and events, and a table to enter the event codes (which could be ommitted from the diagram if there s too much clutter there). This kind of multi-pane visual editing environment has been around for a while in lots of tools, but it s been a lot of effort to build something like this for yourself. One promise of language workbenches is that they make it quite easy to do this, certainly I was easily able to put together a similar example to Figure3quite quickly on my first play with the MetaEdit tool. The tools allows me to define theSemantic Modelfor state machines, define the graphical and tabular editors in Figure3and write a code generator from theSemantic Model. However, while such tools certainly look good, many developers are naturally suspicious of such doodleware tools. There are some very pragmatic reasons why a textual source representation makes sense. As a result other tools head in that direction, providing post-IntelliJ style capabilities such as syntax-directed editing, symbol completion and the like to textual languages. My own suspicion here is that if language workbenches really take off, the languages they ll produce aren t anything like what we consider to be a programming language. One of the common benefits of tools like this is that they allow non-programmers to program. I often sniff at that notion by pointing out that this was the original intent of COBOL. Yet I must also acknowledge a programming environment that has been extremely successful in providing programming tools to non-programmers who program without thinking of themselves of programming - spreadsheets. In programming language terms spreadsheets are based on a quite unusual computational model. Their appeal comes from a very deep integration of the notions of language and tool. Thus it s no surprise that Charles Simonyi combines both a history of development of these kinds of user tools with a long history of developing ideas in language workbenches. As a result I think that language workbenches have a remarkable potential. If they fulfill this they could entirely change the face of software development. This potential, however profound, is still somewhat in the future. It s still early days for language workbenches with new approaches appearing regularly and older tools still subject to deep evolution. As a result I don t have that much to say about them here, as I think they will change quite dramatically during the hoped-for lifetime of this book. But I do have a chapter on them at the end, as I think they are well worth keeping an eye on. Visualization One the great advantages of using a Language Workbench is that this enables you to a wider range of representations of the DSL, in particular graphical representations. However even with a textual DSL you can obtain a diagrammatic representation. Indeed we saw this very early on in this chapter. When looking at Figure1it might have struck you that the diagram was not as neatly drawn as I usually do. The reason for this is that I didn t draw the diagram, I generated it automatically from theSemantic Modelof Miss Grant s controller. Not just do my state machine classes execute, they also are able to render themselves use the dot language. The dot langauge is part of the GraphViz package, which is an open-source tool that allows you to describe mathematical graph structures (nodes and edges) and then automatically plot them. It figures out how to lay out the graph, you just tell it what the nodes and edges are, what shapes to use, and some other hints. Using a tool like GraphViz is extremely helpful for many kinds of DSLs because it gives another representation. Thisvisualizationrepresentation is similar to the DSL itself in that it allows a human to understand the model. The diference between a visualization and the source is that it isn t editable - however it can provide options that are too hard in an editable form, such as a diagram like this. In the terms of a language workbench you can think of a visualization as a read-only projection. It s something that can be less important for graphical language workbenches, since you use a diagram anyway, but it s still sometimes a handy technique. Visualizations don t have to be graphical. I often use a simple textual visualization to help me debug while I m writing a parser. I ve seen people generate visualizations in Excel to help communicate with domain experts. The point is that once you have done the hard work of creating a component framework like this, adding visualizations is really easy. You ll note here that the visualizations are produced from the framework, not the DSL, so you can do this even if you aren t using a DSL to populate the framework. Indeed the techniques in this book can be used for creating visualizations above and beyond DSL usage. A partial parser for a general purpose language can be used to visualize useful aspects of a general purpose program. Any interesting data strucutre can be visualized in interesting ways. Significant Revisions 06 Aug 07 First Draft 09 Apr 08 Split example from general issues
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ブクガ。2014年始動のアイドルグループ。 サクライケンタ プロデュースの変拍子サウンドが特徴。 リンク Twitter 公式サイト Wikipedia 曲など
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今日 - 合計 - SEGA EXTREME SPORTSの攻略ページ 目次 基本情報 [部分編集] ストーリー [部分編集] 攻略情報 [部分編集] Tips [部分編集] プチ情報 [部分編集] 関連動画 [部分編集] 参考文献、参考サイト [部分編集] 感想・レビュー 基本情報 [部分編集] ストーリー [部分編集] 攻略情報 [部分編集] Tips [部分編集] プチ情報 [部分編集] 関連動画 [部分編集] 参考文献、参考サイト [部分編集] 感想・レビュー 名前 コメント 選択肢 投票 役に立った (0) 2012年10月09日 (火) 14時56分54秒 [部分編集] ページごとのメニューの編集はこちらの部分編集から行ってください [部分編集] 編集に関して
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メニュー ①FFBE詐欺ガチャ問題 ①テンプレ ②アヤカ表記無し詐欺問題 ②テンプレ ☆スクエニへの連絡方法 Google/Appleへの連絡はこちら 夢幻の迷宮テンプレ その他通報できそうなもの JARO通報テンプレ まとめ記事など 書き込み募集中 スレ立て案内 リンク @wiki @wikiご利用ガイド ここを編集
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雑誌・MOOK DOLPA FILE SP（ドルパファイルスペシャル） 単行本 リカちゃんBook 公式 リカちゃん完全読本 50th ANNIVERSARY かんたん＆わかりやすい フェルトでつくるリカちゃん手縫い服 オールシーズン Barbie60周年アニバーサリー公式ブック 補足事項 関連項目 出版社別掲載リスト
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☆ メニュー ☆ トップページ アルバム5 アルバム4 アルバム3 アルバム2 アルバム 西遊記メモ 西遊記装備 育成テンプレリンク リンク集 不正行為の報告について コメントページ 更新履歴 取得中です。 ここを編集
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de_portの攻略 （写真・攻略追記など歓迎です） de_port ★爆破設置地点Ａ ★爆破設置地点Ｂ 防衛ポイント1 生存力： 対雑魚： 対BOSS： 対ブラックホール： C4防衛： 意見等はこちらへ 名前 コメント すべてのコメントを見る