Ive looked at them, but I decided bison, just like flex might not be the best or the fastest tools, but they provide lots of information, documentation and tutorials, which makes it much easier to implement them. Creating an ast now that the code is tokenized, and parsed grammatically, we need to figure out how to actually make it work. How can we make sure that when i enter a a 1, that the variable a is actually incremented. Unfortunally, we are still a long way from making that happen, since there are anoth steps that needs to be taken care. Once we have parsed our grammar, we will convert our code into a so-called ast-tree. An Abstract Syntax Tree (ast is a tree-like representation of the code that can easily be processed by a computer. A tree begins with a root-node, this is the start of your program.
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When we are parsing the tokens, the parser will try and match the tokens against the grammar rules provided. If this would be the only place inside our grammar where we would use the T_IF token, it means that a paper t_IF token always is followed by a and after that there might be a variable or a ). Its gold pretty easy to write those grammar rules, as most languages have a fairly small number of rules. Now, if we happen to have written: if a, the tokenizer converts it into T_if t_variable, but the parser will not find a rule that matches, since there are no rules that matches a t_IF followed by a t_variable. At that point, it will throw an syntax error (or you can customize the message it needs to return for instance: Error: an if-statement must be followed by an opening parenthesis. When the complete token-stream is parsed correctly, you have created pretty much your first lint-checker: you can verify if the source-code actually is grammatically correct! Creating these statements from our grammar rules is done automatically by a program called bison. Bison generates a c file from your grammar rules to make your life easier. Never every write your own parser (unless you know what you are doing, and in that case, you wont write a parser anyway but generate them through 3rd party apps like bison. There are others, like antlr and lemon.
Phase 2: parsing From this point we dont have to worry on how a programmer has written his code. Its all converted into generic tokens which we can work with. But just like a natural language like english or Dutch, writing just words down randomly doesnt make it into a sentence that people can understand. The parser phase actually takes the stream of supermarket tokens, and figures out if those tokens actually make sense. For instance, lets assume we have a small bit of code: if (a) The lexer would translate this into tokens: T_if t_parenthesis_open t_variable T_parenthesis_close t_curly_open t_curly_close but suppose we have written something like this: a if Our lexer very happily tokenize this into: T_parenthesis_close T_parenthesis_open t_variable. Now, as said: the parser will take this information and find certain grammar-rules to see if it finds a match. For instance, we could have a grammar-rule describing if-statements: if-statement: T_if t_parenthesis_open t_variable t_parenthesis_close t_if t_parenthesis_open t_parenthesis_close what this does, is telling the parser that an if-statement consists of the T_IF token, followed by a followed by a variable and closed with a ). The second line tells the parser that it could also be a t_IF token, followed by a ( and which would be an empty if-statement (again, it doesnt make sense, but suppose you support it).
Things like variable names are also converted to tokens, which could be the T_variable token (the reviews token itself can hold additional information, in this case, it would be the actual name of the variable, which would be a). The conversion of source-code to tokens is done by a so-called lexer. There are multiple out there, but we decided to use flex for this job. Flex is a pretty old system, but works really well and got lot of documentation and tutorials. This makes it easier to get your write system up and running. The tokenizer also can do things like removing comments and empty lines. Things that makes the code visually easier to read, but are of no use for the compiler. So, phase 1 is complete: a source code is translated into a stream of tokens.
Luckily, this doesnt prevent us from continuing with the rest of the process, but sooner or later we need to have everything documentated and thought out, in order to implement. Step 1: tokenize your code There is a reason why writing a compiler isnt easy, and its the same reason why we implement things like coding standards when we deal with code that is written and/or read by others. If we do things a certain way, it makes it easier to process that information: this is how we define constants, this is how we write an if-else structure, etc etc. For a compiler this works pretty much the same way: it needs to figure out what is what, and in order to do so, it will follow certain rules. Now, the first part in this all is converting your source-code into tokens. For example, there is an T_IF token (the T_ stands for token). So whenever a programmer has written: if (a if(a if (a if(a) or any other possible way to write an if-statement, that if part is replaced by the T_IF token. But some tokens are just single characters. The parenthesis are both tokens as well T_parenthesis_open and T_parenthesis_close for example.
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This and is the easiest step in the whole process, and the only limit is your own imagination. Just write down how your language would look like, what its rules are, how you would do certain stuff. You will run into dead-ends lots of times, since your idea only works for scenario x, but not for scenario. For instance, saffire only supports methods. There are no global functions or procedures like you can find in other languages. This is done to support a more oo type of programming, and so we dont have people printf or str_replace all over the place. Everything is neatly grouped into classes and objects.
But as a side-effect, we are still not 100 sure how we would support anonymous functions, lambdas and closures. But in the end, its just a matter of writing down example code, discuss it with others who find flaws in your reasoning and discuss and decide on a solution. In the end, sooner or later, this will end up in a language specification. This is something that is vital in order to create your compiler: if you have no idea what it will look like, your compiler wont either. With Saffire, we are still in this process: we have decided on a lot of features and specifications, but a lot of things are left open.
Not something that will make it to your desktop soon, but the basic and probably most complex parts of any operating system nevertheless. So i guess its safe to say i know a thing or two about systems. . Unfortunately, all that knowledge is pretty useless when dealing with writing a compiler (or at least: the most important bits of a compiler). But help is on its way: everybody who is into compiler development know about the book that you will need: the (purple) dragon book. If youre a student and use this book in class, you will probably hate.
Other people, like me who never really went to school, and learned it all on the streets, we love this book. Its a bit of dry theory, and you definately have to put away the book once in a while do try to put it all in practice. It will make sense once you get the hang. Now, something like this cannot be written without the help of some smart people who already know this stuff. So a big thank you to, richard van Velzen, who has helped me a lot with getting things up and running. Before you can actually run an application in your language, you have to figure out how the language would work.
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Installing composer: russian roulette. posted on, tagged with: ast bison flex grammar lex saffire yacc. In the thesis last blogpost I was talking about a new language in the making. . Unfortunately, writing a complete new language - from scratch - isnt as easy and takes a fair bit of time. During this development process, i will try and blog a bit on the things we are developing, the problems we are facing and the solutions we are implementing. The current Saffire status: we are able to generate ast trees from Saffire source programs. If you have no clue what Im talking about, no worries: this blogpost will try and explain it all. On writing compilers, ive written some fairly bit of complex code in my life, including an Operating System capable of context switching, memory management, ext2/3, fat16 and vfs capabilities.
dlls, since i have set a limit for incoming e-mails of 60kb on my gmx account. I will send you then an other e-mail address, where you can send the language dll. Last updated: 18-Dec-2014 16:12). Warning : This blogpost has been posted over two years ago. That is a long time in development-world! The story here may not be relevant, complete or secure. Code might not be complete or obsoleted, and even my current vision might have (completely) changed on the subject. So please do read further, but use it with caution. « Saffire: A dive into a new language.
Then change the dll book name in the f file and in the settings of Visual. After this you can edit the resources with Visual. But don't add or delete resource! This may lead to some strange effects. Also you have to replace the entire resource, when new resources will be added to whfc. Then the complete resource must be translated from scratch 8-(.Therefor i have added the getdllver routine. Whenever i made changes to the whfc resources i will increase this number. The actual new version of whfc will check this number and skip all dll's with a non matching number.
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With the language dll you can fully listing customize the look and feel of whfc and translate it in every language you like. To do this you need the sourcecode which contains a project for Visual.0, a small piece of sourcecode and the resources of whfc. Customizing an own language dll, this project generates a "language dll" which must have the following naming convention : whfclang? By a ending, which gives a hint about the language. For the german language you can call it. Whfc searches for all files starting with whfclang and calls Getdlllanguage. The string which must be returned from this function will then be displayed in it's language selection dialog (can be found in the user preferences). The searchpath can be set in the system settings dialog field "Searchpath for language dll's" / Change this variable to your language name static char *c_LangName "English (Example / The dll call for returning the language name char * winapi getdlllanguage(void) return c_LangName; /. Dword winapi getdllver(void) return 4; If you want to generate a new language dll you have to change here the variable c_LangName to your language name.