Grammars for programming languages are written as context-free grammars, . The lexing phase of the compiler or interpreter is sort of a mini. This is presumably what the context-sensitivity of context-sensitive . part of the sentence each word is, and what relation they have to each other. This kind of program is called a parser-generator or compiler-compiler. Computer programmers may find the stack exchange answer to be find more academic introductory materials to be enlightening.
Compiler Design - Syntax Analysis
Syntax is the means you use to convey it, i. Typically, you will use the word dog to convey the idea of a dog. The word dog is made of three letters, or some equivalent sound, and is intended to be the representation of some kind of animal. The key idea is that communication is done through representation of what is to be communicated. Representation structures are usually called syntax, while what is represented is called semantics.
This goes more or less for natural language as well as for programming languages. Words are syntactic entities to represent more or less elementary semantic concepts.
Compiler Design - Syntax Analysis
But these elementary concepts have to be put together in a variety of ways to give more complex meaning. We write the dog to convey that we mean a specific dog, and the dog bites the cat to convey a more complex idea. But the way the words are organized has to be fixed by rules, so that we can tell which of the dog and the cat is actually biting the other.
These rules are syntactic rules, since they tell us how the representation of our message is to be organized. The same is true in mathematics. You have mathematical expression written with a very formal syntax. Some of the rules are: Programming languages are semantically specialized in expressing computations to be performed, rather than expressing problems to be solved, proof of theorems or friendly relations between animal.
But that is the main difference. Representations used in syntax are usually strings of characters, or of sounds for spoken languages.
Context-free grammar - Wikipedia
Semantics usually belong to abstract domain, or possibly to reality, but still abstracted in our thought processes, or to the behavioral domain of devices. The result in then interpreted in whatever way by the receiver.
So what we see of the language is mostly syntax and its structure. The example above are only one of the most common way to define syntactic strings and their structural organization. For a given language, some strings can be assigned a structure, and are said to belong to the language, while others do not.
The same is true for words. Some sequences of letters or sound are legitimate words, while other are not.
Formal languages are just syntax without semantics. They define with a set of rule what sequences can be constructed, using the basic elements of an alphabet.
What the rules are can be very variable, sometimes complex. The program will parse the sentence, find the structure, and run your instructions on each part of the structure.
This kind of program is called a parser-generator or compiler-compiler. This kind of language analysis was invented for automatic analysis of natural language such as English but it turns out that this is most useful for analyzing computer languages. A language designer can write a grammar which captures his new language, then run it through the parser-generator to get a program which parses his language, and translates, interprets, compiles, executes, etc if he wants.
In fact, in most cases you can't really do this. For instance, balanced parentheses are a context-free language, but a language where it is required to declare all variables before you use them is context-sensitive.Context Free Grammar , Derivation of strings and Tree
The parser is a part of the compiler, but additional logic is required to enforce these other requirements. What you then have to do is write a grammar which captures as much of your language as possible, run that through a parser-generator, then write code which enforces the rest of the requirements symbol table handler, etc.
We don't generally use context-sensitive grammars because they are much more poorly supported. I don't know if there is an equivalent to an LR k parser-generator for context-sensitive languages. Yes, a Turing machine or linear bound machine can parse one, but I don't know if there is a general algorithm for turning a context-sensitive grammar into a program for a Turing machine, in the sense that an LR 1 generator makes parse tables for a pushdown machine.
My guess is that the tables which underlie the parser would be exponentially larger. Whether a language is context-free or not has nothing to do with it being functional. It is simply a matter of how complex the language rules and features are to parse. Here's a CFG for the imperative language Brainfuck: Usually, context-free grammars CFGs are only used to roughly specify the syntax of a language. One must distinguish between syntactically correct programs and programs that compile.
Most commonly, compilers split language analysis into syntax analysis that builds and verifies the general structure of a piece of code, and semantic analysis that verifies the meaning of the program. If by "context-free language" you mean " Languages that fit this bill hardly have any rules or complicated features, like the existence of variables, whitespace-sensitivity, a type system, or any other context: Information defined in one place and relied upon in another. If, on the other hand, "context-free language" only means "