Bison c grammar file

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. It was done in the past, before the egcs fork stuff.

I cannot give you the exact version and location, but i can tell you that it should be in the 2. GCC of version 4. Parsing and semantical analysis were performed simultaneously, without presenting syntax tree as a separate data structure. You will have to go back several versions to locate the grammar in bison format, but it is out there. You should try google's code search with. It will be old, though. The C grammar can be found in comments in c-parser.

Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 11 years, 8 months ago. Active 6 years, 9 months ago. Viewed 10k times. Haruki Haruki 1 1 gold badge 8 8 silver badges 24 24 bronze badges. That's more of a statement than a question? I decided to reciprocate by phrasing my statement as a question. Did you try googling?

This might lead to some illegal reductions. But it will not matter because the error will be caught ultimately before another shift can take place. Taking the above two aspects into consideration, our dragon book style table will now change considerably. And there is no "accept" entry in the table any more.

State 8 simply is an accepting state. The table given below is constructed directly from the. This is not the table that will be used for parsing in a Bison generated parser. This table here is only to gain a perspective on how the final tables will look like. The table constructed from the Bison report file is matched with our hand computed table.

State 1 generated by Bison corresponds to state 12 in our table and so on. Bison assigns a symbol number to each grammar symbol terminal or non-terminal.

Of course Bison has its own symbol table like any other compiler Bison is a compiler compiler remember. As a rule, Bison always assigns numbers to terminal symbols first and then proceeds to non-terminals. Symbol number 0 is reserved for this symbol. Symbol number 1 is reserved for it.

Symbol number 2 is reserved for this symbol. Numbers for terminals begin from 3 onwards. You can check the symbol numbers assigned to various symbols by looking at the yytname array generated in the output parser. For our example grammar, the symbol numbers look like this:. Symbols 0 through 7 are terminals and the rest are non-terminals.

These symbol numbers are used to index various tables as we will see in a moment. Let us look at how we can optimally represent our 'modified traditional table'.

The table is still a sparse matrix with a lot of white space and repeated information. We can start by collecting all repeated data at one place. The default reductions are our prime targets. They can all be listed in an array indexed by state number:. We did waste some space for states where there are no default reductions, but that is far less than all the locations used up for repeating reduce actions. Some of the states have only reduce actions and nothing else.

So, these rows are pretty much "taken care of" by the above array. Observe that we have listed a default reduction for state 2 r7 even though it had shift actions on a couple of symbols. Hence, this array may be used only after ensuring that there are no shift actions for the current state on the current look-ahead symbol.

The next obvious target would be the GOTO part of the table which is mostly empty. Since most states do not have a GOTO part, the best space saving scheme here would be to have an array indexed by non-terminal column instead of state row. But each non-terminal can have a different GOTO state depending on the current state of the automaton.

So, we choose to list out the most popular GOTO state of each non-terminal in an array like this:. That's one entry each for non-terminals L, E, P, M. For now this table has saved us a lot of wasted GOTO white space. To compress this part of the table, Bison follows a method described by Tarjan and Yao [3]. It is a fairly complex method combining the idea of Trie data structures and "double displacement" with some of the authors' own ideas thrown in to improve time and space complexity results.

Double displacement is very straight forward. We flatten out the above 2-D table into a simple one dimensional array by mapping all non-white-space entries into some location of the array. We keep the order of elements in each row intact and displace each row by some amount such that no two non-white-space entries in each row occupy the same position in the one-dimensional array.

Here is a sample displacement table and the corresponding one dimensional table:. Even with the above scheme we have a lot of repeated entries in the table T which are really the same states e. So this method is combined with column displacements and "Tries" to obtain a more compressed table organization.

If this discussion has whet your appetite for more, you can refer to [3] for more details. The final objective of Bison is to build a one-dimensional table T that specifies what to do in each state. This table will be indexed by a one dimensional directory table D.

In the above discussion, displacements into T are indexed by the 2-D array index i,j. But we would rather want to index into T by state number and symbol number instead since the rows and columns of the 2D table are headed by states and symbols. Bison indexes D by state number and displacement into T by symbol number. If the next look-ahead symbol has number k, table entry for current state can be retrieved as follows:.

As an example, the action for state 0 is s1 on symbol number 5 'a'. But there is a special case that we need to take care of. There can be some 'explicit' errors in the action table that cannot be over written by default reductions. To represent these reductions in the same table T, Bison generates negated rule numbers in T.

The negative sign is just to differentiate the shifts which are positive and represent state numbers from the reductions. We do not have this situation in our grammar. Also D will have a specially defined negative value that will indicate that the current state has only a default reduction like state 1 for example. The parser would always go for a default reduction if this value is encountered in D. This table will contain one reference entry for each non-terminal symbol.

These entries are displacements in T, but indexed by state number. Bison also has a guard table that is checked to see if we are within legal bounds of table T.