Posted by: shahryar on Jun 09, Brian: Are you using the latest stable release? Posted by: shahryar on Jun 30, In Slackware In kannel gateway There is no error, but a lot of "nothing to be done for all" thing. Posted by: Serina Wang on Apr 18, GNU M4 1. Glibc 2.
Posted by: mehdi on Aug 08, Posted by: shahryar on Aug 18, Welcome to Geeksww. Click here. Note: check for any error message. Compile Bison: make Note: check for any error message.
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This chapter introduces many of the basic concepts without which the details of Bison will not make sense. If you do not already know how to use Bison or Yacc, we suggest you start by reading this chapter carefully. In order for Bison to parse a language, it must be described by a context-free grammar. This means that you specify one or more syntactic groupings and give rules for constructing them from their parts.
As you can see, rules are often recursive, but there must be at least one rule which leads out of the recursion. Any grammar expressed in BNF is a context-free grammar.
The input to Bison is essentially machine-readable BNF. There are various important subclasses of context-free grammars. Although it can handle almost all context-free grammars, Bison is optimized for what are called LR 1 grammars. In brief, in these grammars, it must be possible to tell how to parse any portion of an input string with just a single token of lookahead.
For historical reasons, Bison by default is limited by the additional restrictions of LALR 1 , which is hard to explain simply. See Mysterious Conflicts , for more information on this. See LR Table Construction , to learn how. Parsers for LR 1 grammars are deterministic , meaning roughly that the next grammar rule to apply at any point in the input is uniquely determined by the preceding input and a fixed, finite portion called a lookahead of the remaining input.
A context-free grammar can be ambiguous , meaning that there are multiple ways to apply the grammar rules to get the same inputs. Even unambiguous grammars can be nondeterministic , meaning that no fixed lookahead always suffices to determine the next grammar rule to apply. With the proper declarations, Bison is also able to parse these more general context-free grammars, using a technique known as GLR parsing for Generalized LR.
In the formal grammatical rules for a language, each kind of syntactic unit or grouping is named by a symbol. We call a piece of input corresponding to a single terminal symbol a token , and a piece corresponding to a single nonterminal symbol a grouping.
We can use the C language as an example of what symbols, terminal and nonterminal, mean. The tokens of C are identifiers, constants numeric and string , and the various keywords, arithmetic operators and punctuation marks. These tokens can be subdivided into characters, but that is a matter of lexicography, not grammar. The syntactic groupings of C include the expression, the statement, the declaration, and the function definition.
The full grammar uses dozens of additional language constructs, each with its own nonterminal symbol, in order to express the meanings of these four. The example above is a function definition; it contains one declaration, and one statement.
Each nonterminal symbol must have grammatical rules showing how it is made out of simpler constructs. For example, one kind of C statement is the return statement; this would be described with a grammar rule which reads informally as follows:. One nonterminal symbol must be distinguished as the special one which defines a complete utterance in the language.
It is called the start symbol. In a compiler, this means a complete input program. The Bison parser reads a sequence of tokens as its input, and groups the tokens using the grammar rules. If not, the parser reports a syntax error.
A formal grammar is a mathematical construct. To define the language for Bison, you must write a file expressing the grammar in Bison syntax: a Bison grammar file. See Bison Grammar Files.
A nonterminal symbol in the formal grammar is represented in Bison input as an identifier, like an identifier in C. By convention, it should be in lower case, such as expr , stmt or declaration. The Bison representation for a terminal symbol is also called a token kind. Token kinds as well can be represented as C-like identifiers. A terminal symbol that stands for a particular keyword in the language should be named after that keyword converted to upper case.
The terminal symbol error is reserved for error recovery. See Symbols, Terminal and Nonterminal. A terminal symbol can also be represented as a character literal, just like a C character constant. You should do this whenever a token is just a single character parenthesis, plus-sign, etc. A third way to represent a terminal symbol is with a C string constant containing several characters. See Symbols, Terminal and Nonterminal , for more information.
The grammar rules also have an expression in Bison syntax. For example, here is the Bison rule for a C return statement. The semicolon in quotes is a literal character token, representing part of the C syntax for the statement; the naked semicolon, and the colon, are Bison punctuation used in every rule.
But the precise value is very important for what the input means once it is parsed. A compiler is useless if it fails to distinguish between 4, 1 and as constants in the program! Therefore, each token in a Bison grammar has both a token kind and a semantic value. See Defining Language Semantics , for details. It tells everything you need to know to decide where the token may validly appear and how to group it with other tokens.
The grammar rules know nothing about tokens except their kinds. The semantic value has all the rest of the information about the meaning of the token, such as the value of an integer, or the name of an identifier.
Each grouping can also have a semantic value as well as its nonterminal symbol. For example, in a calculator, an expression typically has a semantic value that is a number. In a compiler for a programming language, an expression typically has a semantic value that is a tree structure describing the meaning of the expression. In order to be useful, a program must do more than parse input; it must also produce some output based on the input.
In a Bison grammar, a grammar rule can have an action made up of C statements. Each time the parser recognizes a match for that rule, the action is executed.
See Actions. Most of the time, the purpose of an action is to compute the semantic value of the whole construct from the semantic values of its parts. For example, suppose we have a rule which says an expression can be the sum of two expressions.
When the parser recognizes such a sum, each of the subexpressions has a semantic value which describes how it was built up. The action for this rule should create a similar sort of value for the newly recognized larger expression. The action says how to produce the semantic value of the sum expression from the values of the two subexpressions.
That is, it may not be able to decide on the basis of the input read so far which of two possible reductions applications of a grammar rule applies, or whether to apply a reduction or read more of the input and apply a reduction later in the input. To use a grammar that is not easily modified to be LR 1 , a more general parsing algorithm is sometimes necessary.
These parsers handle Bison grammars that contain no unresolved conflicts i. Each of the resulting parsers can again split, so that at any given time, there can be any number of possible parses being explored. The parsers proceed in lockstep; that is, all of them consume shift a given input symbol before any of them proceed to the next. Each of the cloned parsers eventually meets one of two possible fates: either it runs into a parsing error, in which case it simply vanishes, or it merges with another parser, because the two of them have reduced the input to an identical set of symbols.
During the time that there are multiple parsers, semantic actions are recorded, but not performed. When a parser disappears, its recorded semantic actions disappear as well, and are never performed. When a reduction makes two parsers identical, causing them to merge, Bison records both sets of semantic actions.
Whenever the last two parsers merge, reverting to the single-parser case, Bison resolves all the outstanding actions either by precedences given to the grammar rules involved, or by performing both actions, and then calling a designated user-defined function on the resulting values to produce an arbitrary merged result. In the simplest cases, you can use the GLR algorithm to parse grammars that are unambiguous but fail to be LR 1.
Such grammars typically require more than one symbol of lookahead. Consider a problem that arises in the declaration of enumerated and subrange types in the programming language Pascal. Here are some examples:. This gives rise to the following situation, containing a superfluous pair of parentheses:. These declarations are contrived, but they are syntactically valid, and more-complicated cases can come up in practical programs. You might think of using the lexer to distinguish between the two forms by returning different tokens for currently defined and undefined identifiers.
So this approach cannot work. A simple solution to this problem is to declare the parser to use the GLR algorithm. When the GLR parser reaches the critical state, it merely splits into two branches and pursues both syntax rules simultaneously. Sooner or later, one of them runs into a parsing error. So one of the branches fails silently, and the other one continues normally, performing all the intermediate actions that were postponed during the split.
If the input is syntactically incorrect, both branches fail and the parser reports a syntax error as usual. In this example, LR 2 would suffice, but also some cases that are not LR k for any k can be handled this way.
In general, a GLR parser can take quadratic or cubic worst-case time, and the current Bison parser even takes exponential time and space for some grammars. In practice, this rarely happens, and for many grammars it is possible to prove that it cannot happen. The present example contains only one conflict between two rules, and the type-declaration context containing the conflict cannot be nested.
So the number of branches that can exist at any time is limited by the constant 2, and the parsing time is still linear. Here is a Bison grammar corresponding to the example above. It parses a vastly simplified form of Pascal type declarations.
In the conflicting situation the parser chooses one of the alternatives, arbitrarily the one declared first. Therefore the following correct input is not recognized:.
No change in the grammar itself is required. Now the parser recognizes all valid declarations, according to the limited syntax above, transparently. In fact, the user does not even notice when the parser splits. So here we have a case where we can use the benefits of GLR, almost without disadvantages.
Even in simple cases like this, however, there are at least two potential problems to beware. First, always analyze the conflicts reported by Bison to make sure that GLR splitting is only done where it is intended. A GLR parser splitting inadvertently may cause problems less obvious than an LR parser statically choosing the wrong alternative in a conflict.
Second, consider interactions with the lexer see Semantic Info in Token Kinds with great care. Since a split parser consumes tokens without performing any actions during the split, the lexer cannot obtain information via parser actions. Some cases of lexer interactions can be eliminated by using GLR to shift the complications from the lexer to the parser. You must check the remaining cases for correctness. In our example, it would be safe for the lexer to return tokens based on their current meanings in some symbol table, because no new symbols are defined in the middle of a type declaration.
Though it is possible for a parser to define the enumeration constants as they are parsed, before the type declaration is completed, it actually makes no difference since they cannot be used within the same enumerated type declaration. For example,. We say that these parses have merged. At this point, the GLR parser requires a specification in the grammar of how to choose between the competing parses.
The parser therefore prints. Consider a different input string for this parser:. Here, there is no ambiguity this cannot be parsed as a declaration. In this case, no precedence declaration is used.
Again, the parser splits into two, one assuming that x is an expr , and the other assuming x is a declarator. Suppose that instead of resolving the ambiguity, you wanted to see all the possibilities. For this purpose, you must merge the semantic actions of the two possible parsers, rather than choosing one over the other. To do so, you could change the declaration of stmt as follows:.
With these declarations, the resulting parser parses the first example as both an expr and a decl , and prints. Otherwise, the ambiguity would be unresolvable, and the parser will report an error during any parse that results in the offending merge.
The signature of the merger depends on the type of the symbol. In the previous example, the merged-to symbol stmt does not have a specific type, and the merger is. If you have an opinion about it, please let us know. The nature of GLR parsing and the structure of the generated parsers give rise to certain restrictions on semantic values and actions.
By definition, a deferred semantic action is not performed at the same time as the associated reduction. This raises caveats for several Bison features you might use in a semantic action in a GLR parser. In any semantic action, you can examine yychar to determine the kind of the lookahead token present at the time of the associated reduction.
In a nondeferred semantic action, you can also modify any of these variables to influence syntax analysis.
See Lookahead Tokens. In this case, yychar , yylval , and yylloc are set to shallow copies of the values they had at the time of the associated reduction. For this reason alone, modifying them is dangerous.
Moreover, the result of modifying them is undefined and subject to change with future versions of Bison. For example, if a semantic action might be deferred, you should never write it to invoke yyclearin see Special Features for Use in Actions or to attempt to free memory referenced by yylval.
The effect in a deferred action is similar, but the precise point of the error is undefined; instead, the parser reverts to deterministic operation, selecting an unspecified stack on which to continue with a syntax error. If the expression yields 0 false , the clause is treated as a syntax error, which, in a nondeterministic parser, causes the stack in which it is reduced to die. As the example shows, predicates otherwise look like semantic actions, and therefore you must take them into account when determining the numbers to use for denoting the semantic values of right-hand side symbols.
Predicate actions, however, have no defined value, and may not be given labels. There is a subtle difference between semantic predicates and ordinary actions in nondeterministic mode, since the latter are deferred. For example, we could try to rewrite the previous example as. It therefore reports an error. Finally, be careful in writing predicates: deferred actions have not been evaluated, so that using them in a predicate will have undefined effects.
Many applications, like interpreters or compilers, have to produce verbose and useful error messages. To achieve this, one must be able to keep track of the textual location , or location , of each syntactic construct. Bison provides a mechanism for handling these locations. Each token has a semantic value. In a similar fashion, each token has an associated location, but the type of locations is the same for all tokens and groupings. Moreover, the output parser is equipped with a default data structure for storing locations see Tracking Locations , for more details.
Like semantic values, locations can be reached in actions using a dedicated set of constructs. When a rule is matched, a default action is used to compute the semantic value of its left hand side see Actions. In the same way, another default action is used for locations. When building a new location for a given grouping, the default behavior of the output parser is to take the beginning of the first symbol, and the end of the last symbol. When you run Bison, you give it a Bison grammar file as input.
The most important output is a C source file that implements a parser for the language described by the grammar. This parser is called a Bison parser , and this file is called a Bison parser implementation file. Keep in mind that the Bison utility and the Bison parser are two distinct programs: the Bison utility is a program whose output is the Bison parser implementation file that becomes part of your program.
The job of the Bison parser is to group tokens into groupings according to the grammar rules—for example, to build identifiers and operators into expressions. As it does this, it runs the actions for the grammar rules it uses.
The tokens come from a function called the lexical analyzer that you must supply in some fashion such as by writing it in C. The Bison parser calls the lexical analyzer each time it wants a new token. Java is also supported as an experimental feature. It can also be found on the GNU mirrors ; please use a mirror if possible. Documentation for Bison is available online, as is documentation for most GNU software. A brief summary is available by running bison --help.
Announcements about Bison and most other GNU software are made on info-gnu archive. Security reports that should not be made immediately public can be sent directly to the maintainer. If there is no response to an urgent issue, you can escalate to the general security mailing list for advice. You can try to download the pkgs of bison 2.
Or you can also try to download source package of bison to install a specified version of bison. After installed Bison on your Ubuntu Linux, you can try to check the current installed version of Bison with the following command:. You should know that how to download and install Bison package on Ubuntu
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