<head>
<title>The Lemon Parser Generator</title>
</head>
-<body bgcolor=white>
-<h1 align=center>The Lemon Parser Generator</h1>
+<body bgcolor='white'>
+<h1 align='center'>The Lemon Parser Generator</h1>
<p>Lemon is an LALR(1) parser generator for C.
It does the same job as "bison" and "yacc".
-But lemon is not a bison or yacc clone. Lemon
+But Lemon is not a bison or yacc clone. Lemon
uses a different grammar syntax which is designed to
reduce the number of coding errors. Lemon also uses a
parsing engine that is faster than yacc and
has also been updated so that it too can generate a
reentrant and threadsafe parser.)
Lemon also implements features that can be used
-to eliminate resource leaks, making is suitable for use
+to eliminate resource leaks, making it suitable for use
in long-running programs such as graphical user interfaces
or embedded controllers.</p>
applications. But the user is free to substitute a different parser
template if desired.</p>
-<p>Depending on command-line options, Lemon will generate between
-one and three files of outputs.
+<p>Depending on command-line options, Lemon will generate up to
+three output files.
<ul>
<li>C code to implement the parser.
<li>A header file defining an integer ID for each terminal symbol.
You can obtain a list of the available command-line options together
with a brief explanation of what each does by typing
<pre>
- lemon -?
+ lemon "-?"
</pre>
As of this writing, the following command-line options are supported:
<ul>
<li><b>-b</b>
Show only the basis for each parser state in the report file.
<li><b>-c</b>
-Do not compress the generated action tables.
+Do not compress the generated action tables. The parser will be a
+little larger and slower, but it will detect syntax errors sooner.
<li><b>-D<i>name</i></b>
-Define C preprocessor macro <i>name</i>. This macro is useable by
-"%ifdef" lines in the grammar file.
+Define C preprocessor macro <i>name</i>. This macro is usable by
+"<tt><a href='#pifdef'>%ifdef</a></tt>" and
+"<tt><a href='#pifdef'>%ifndef</a></tt>" lines
+in the grammar file.
<li><b>-g</b>
Do not generate a parser. Instead write the input grammar to standard
output with all comments, actions, and other extraneous text removed.
Omit "#line" directives in the generated parser C code.
<li><b>-m</b>
Cause the output C source code to be compatible with the "makeheaders"
-program.
+program.
<li><b>-p</b>
-Display all conflicts that are resolved by
+Display all conflicts that are resolved by
<a href='#precrules'>precedence rules</a>.
<li><b>-q</b>
Suppress generation of the report file.
</pre>
The first argument to the Parse() routine is the pointer returned by
ParseAlloc().
-The second argument is a small positive integer that tells the parse the
+The second argument is a small positive integer that tells the parser the
type of the next token in the data stream.
There is one token type for each terminal symbol in the grammar.
The gram.h file generated by Lemon contains #define statements that
A value of 0 for the second argument is a special flag to the
parser to indicate that the end of input has been reached.
The third argument is the value of the given token. By default,
-the type of the third argument is integer, but the grammar will
+the type of the third argument is "void*", but the grammar will
usually redefine this type to be some kind of structure.
Typically the second argument will be a broad category of tokens
such as "identifier" or "number" and the third argument will
<p>The Parse() function may have either three or four arguments,
depending on the grammar. If the grammar specification file requests
-it (via the <a href='#extraarg'><tt>extra_argument</tt> directive</a>),
+it (via the <tt><a href='#extraarg'>%extra_argument</a></tt> directive),
the Parse() function will have a fourth parameter that can be
of any type chosen by the programmer. The parser doesn't do anything
with this argument except to pass it through to action routines.
<p>A typical use of a Lemon parser might look something like the
following:
<pre>
- 01 ParseTree *ParseFile(const char *zFilename){
- 02 Tokenizer *pTokenizer;
- 03 void *pParser;
- 04 Token sToken;
- 05 int hTokenId;
- 06 ParserState sState;
- 07
- 08 pTokenizer = TokenizerCreate(zFilename);
- 09 pParser = ParseAlloc( malloc );
- 10 InitParserState(&sState);
- 11 while( GetNextToken(pTokenizer, &hTokenId, &sToken) ){
- 12 Parse(pParser, hTokenId, sToken, &sState);
+ 1 ParseTree *ParseFile(const char *zFilename){
+ 2 Tokenizer *pTokenizer;
+ 3 void *pParser;
+ 4 Token sToken;
+ 5 int hTokenId;
+ 6 ParserState sState;
+ 7
+ 8 pTokenizer = TokenizerCreate(zFilename);
+ 9 pParser = ParseAlloc( malloc );
+ 10 InitParserState(&sState);
+ 11 while( GetNextToken(pTokenizer, &hTokenId, &sToken) ){
+ 12 Parse(pParser, hTokenId, sToken, &sState);
13 }
- 14 Parse(pParser, 0, sToken, &sState);
+ 14 Parse(pParser, 0, sToken, &sState);
15 ParseFree(pParser, free );
16 TokenizerFree(pTokenizer);
17 return sState.treeRoot;
We assume the existence of some kind of tokenizer which is created
using TokenizerCreate() on line 8 and deleted by TokenizerFree()
on line 16. The GetNextToken() function on line 11 retrieves the
-next token from the input file and puts its type in the
+next token from the input file and puts its type in the
integer variable hTokenId. The sToken variable is assumed to be
some kind of structure that contains details about each token,
-such as its complete text, what line it occurs on, etc. </p>
+such as its complete text, what line it occurs on, etc.</p>
<p>This example also assumes the existence of structure of type
ParserState that holds state information about a particular parse.
<pre>
ParseFile(){
pParser = ParseAlloc( malloc );
- while( GetNextToken(pTokenizer,&hTokenId, &sToken) ){
+ while( GetNextToken(pTokenizer,&hTokenId, &sToken) ){
Parse(pParser, hTokenId, sToken);
}
Parse(pParser, 0, sToken);
Most of the work in using Lemon is in writing an appropriate
grammar file.</p>
-<p>The grammar file for lemon is, for the most part, free format.
+<p>The grammar file for Lemon is, for the most part, free format.
It does not have sections or divisions like yacc or bison. Any
declaration can occur at any point in the file.
Lemon ignores whitespace (except where it is needed to separate
-tokens) and it honors the same commenting conventions as C and C++.</p>
+tokens), and it honors the same commenting conventions as C and C++.</p>
<h3>Terminals and Nonterminals</h3>
<p>A terminal symbol (token) is any string of alphanumeric
and/or underscore characters
-that begins with an upper case letter.
+that begins with an uppercase letter.
A terminal can contain lowercase letters after the first character,
-but the usual convention is to make terminals all upper case.
+but the usual convention is to make terminals all uppercase.
A nonterminal, on the other hand, is any string of alphanumeric
-and underscore characters than begins with a lower case letter.
-Again, the usual convention is to make nonterminals use all lower
-case letters.</p>
+and underscore characters than begins with a lowercase letter.
+Again, the usual convention is to make nonterminals use all lowercase
+letters.</p>
-<p>In Lemon, terminal and nonterminal symbols do not need to
+<p>In Lemon, terminal and nonterminal symbols do not need to
be declared or identified in a separate section of the grammar file.
Lemon is able to generate a list of all terminals and nonterminals
by examining the grammar rules, and it can always distinguish a
rule can be empty.
Rules can occur in any order, except that the left-hand side of the
first rule is assumed to be the start symbol for the grammar (unless
-specified otherwise using the <tt>%start</tt> directive described below.)
+specified otherwise using the <tt><a href='#start_symbol'>%start_symbol</a></tt>
+directive described below.)
A typical sequence of grammar rules might look something like this:
<pre>
expr ::= expr PLUS expr.
names in the action.
In yacc or bison, one would write this:
<pre>
- expr -> expr PLUS expr { $$ = $1 + $3; };
+ expr -> expr PLUS expr { $$ = $1 + $3; };
</pre>
But in Lemon, the same rule becomes the following:
<pre>
whichever rule comes first in the grammar file.</p>
<p>Just like in
-yacc and bison, Lemon allows a measure of control
-over the resolution of paring conflicts using precedence rules.
+yacc and bison, Lemon allows a measure of control
+over the resolution of parsing conflicts using precedence rules.
A precedence value can be assigned to any terminal symbol
-using the
-<a href='#pleft'>%left</a>,
-<a href='#pright'>%right</a> or
-<a href='#pnonassoc'>%nonassoc</a> directives. Terminal symbols
-mentioned in earlier directives have a lower precedence that
+using the
+<tt><a href='#pleft'>%left</a></tt>,
+<tt><a href='#pright'>%right</a></tt> or
+<tt><a href='#pnonassoc'>%nonassoc</a></tt> directives. Terminal symbols
+mentioned in earlier directives have a lower precedence than
terminal symbols mentioned in later directives. For example:</p>
<p><pre>
<li> If the precedence of the token to be shifted is greater than
the precedence of the rule to reduce, then resolve in favor
of the shift. No parsing conflict is reported.
-<li> If the precedence of the token it be shifted is less than the
+<li> If the precedence of the token to be shifted is less than the
precedence of the rule to reduce, then resolve in favor of the
reduce action. No parsing conflict is reported.
<li> If the precedences are the same and the shift token is
right-associative, then resolve in favor of the shift.
No parsing conflict is reported.
-<li> If the precedences are the same the shift token is
+<li> If the precedences are the same and the shift token is
left-associative, then resolve in favor of the reduce.
No parsing conflict is reported.
-<li> Otherwise, resolve the conflict by doing the shift and
- report the parsing conflict.
+<li> Otherwise, resolve the conflict by doing the shift, and
+ report a parsing conflict.
</ul>
Reduce-reduce conflicts are resolved this way:
<ul>
-<li> If either reduce rule
+<li> If either reduce rule
lacks precedence information, then resolve in favor of the
- rule that appears first in the grammar and report a parsing
+ rule that appears first in the grammar, and report a parsing
conflict.
-<li> If both rules have precedence and the precedence is different
+<li> If both rules have precedence and the precedence is different,
then resolve the dispute in favor of the rule with the highest
- precedence and do not report a conflict.
+ precedence, and do not report a conflict.
<li> Otherwise, resolve the conflict by reducing by the rule that
- appears first in the grammar and report a parsing conflict.
+ appears first in the grammar, and report a parsing conflict.
</ul>
<h3>Special Directives</h3>
directives. We've described all the grammar rules, so now we'll
talk about the special directives.</p>
-<p>Directives in lemon can occur in any order. You can put them before
-the grammar rules, or after the grammar rules, or in the mist of the
+<p>Directives in Lemon can occur in any order. You can put them before
+the grammar rules, or after the grammar rules, or in the midst of the
grammar rules. It doesn't matter. The relative order of
directives used to assign precedence to terminals is important, but
other than that, the order of directives in Lemon is arbitrary.</p>
<p>Lemon supports the following special directives:
<ul>
-<li><tt>%code</tt>
-<li><tt>%default_destructor</tt>
-<li><tt>%default_type</tt>
-<li><tt>%destructor</tt>
-<li><tt>%endif</tt>
-<li><tt>%extra_argument</tt>
-<li><tt>%fallback</tt>
-<li><tt>%ifdef</tt>
-<li><tt>%ifndef</tt>
-<li><tt>%include</tt>
-<li><tt>%left</tt>
-<li><tt>%name</tt>
-<li><tt>%nonassoc</tt>
-<li><tt>%parse_accept</tt>
-<li><tt>%parse_failure </tt>
-<li><tt>%right</tt>
-<li><tt>%stack_overflow</tt>
-<li><tt>%stack_size</tt>
-<li><tt>%start_symbol</tt>
-<li><tt>%syntax_error</tt>
-<li><tt>%token_class</tt>
-<li><tt>%token_destructor</tt>
-<li><tt>%token_prefix</tt>
-<li><tt>%token_type</tt>
-<li><tt>%type</tt>
-<li><tt>%wildcard</tt>
+<li><tt><a href='#pcode'>%code</a></tt>
+<li><tt><a href='#default_destructor'>%default_destructor</a></tt>
+<li><tt><a href='#default_type'>%default_type</a></tt>
+<li><tt><a href='#destructor'>%destructor</a></tt>
+<li><tt><a href='#pifdef'>%endif</a></tt>
+<li><tt><a href='#extraarg'>%extra_argument</a></tt>
+<li><tt><a href='#pfallback'>%fallback</a></tt>
+<li><tt><a href='#pifdef'>%ifdef</a></tt>
+<li><tt><a href='#pifdef'>%ifndef</a></tt>
+<li><tt><a href='#pinclude'>%include</a></tt>
+<li><tt><a href='#pleft'>%left</a></tt>
+<li><tt><a href='#pname'>%name</a></tt>
+<li><tt><a href='#pnonassoc'>%nonassoc</a></tt>
+<li><tt><a href='#parse_accept'>%parse_accept</a></tt>
+<li><tt><a href='#parse_failure'>%parse_failure</a></tt>
+<li><tt><a href='#pright'>%right</a></tt>
+<li><tt><a href='#stack_overflow'>%stack_overflow</a></tt>
+<li><tt><a href='#stack_size'>%stack_size</a></tt>
+<li><tt><a href='#start_symbol'>%start_symbol</a></tt>
+<li><tt><a href='#syntax_error'>%syntax_error</a></tt>
+<li><tt><a href='#token_class'>%token_class</a></tt>
+<li><tt><a href='#token_destructor'>%token_destructor</a></tt>
+<li><tt><a href='#token_prefix'>%token_prefix</a></tt>
+<li><tt><a href='#token_type'>%token_type</a></tt>
+<li><tt><a href='#ptype'>%type</a></tt>
+<li><tt><a href='#pwildcard'>%wildcard</a></tt>
</ul>
Each of these directives will be described separately in the
following sections:</p>
<a name='pcode'></a>
<h4>The <tt>%code</tt> directive</h4>
-<p>The %code directive is used to specify addition C code that
+<p>The <tt>%code</tt> directive is used to specify additional C code that
is added to the end of the main output file. This is similar to
-the <a href='#pinclude'>%include</a> directive except that %include
-is inserted at the beginning of the main output file.</p>
+the <tt><a href='#pinclude'>%include</a></tt> directive except that
+<tt>%include</tt> is inserted at the beginning of the main output file.</p>
-<p>%code is typically used to include some action routines or perhaps
-a tokenizer or even the "main()" function
+<p><tt>%code</tt> is typically used to include some action routines or perhaps
+a tokenizer or even the "main()" function
as part of the output file.</p>
<a name='default_destructor'></a>
<h4>The <tt>%default_destructor</tt> directive</h4>
-<p>The %default_destructor directive specifies a destructor to
+<p>The <tt>%default_destructor</tt> directive specifies a destructor to
use for non-terminals that do not have their own destructor
-specified by a separate %destructor directive. See the documentation
-on the <a name='#destructor'>%destructor</a> directive below for
+specified by a separate <tt>%destructor</tt> directive. See the documentation
+on the <tt><a name='#destructor'>%destructor</a></tt> directive below for
additional information.</p>
-<p>In some grammers, many different non-terminal symbols have the
-same datatype and hence the same destructor. This directive is
-a convenience way to specify the same destructor for all those
+<p>In some grammars, many different non-terminal symbols have the
+same data type and hence the same destructor. This directive is
+a convenient way to specify the same destructor for all those
non-terminals using a single statement.</p>
<a name='default_type'></a>
<h4>The <tt>%default_type</tt> directive</h4>
-<p>The %default_type directive specifies the datatype of non-terminal
-symbols that do no have their own datatype defined using a separate
-<a href='#ptype'>%type</a> directive.
-</p>
+<p>The <tt>%default_type</tt> directive specifies the data type of non-terminal
+symbols that do not have their own data type defined using a separate
+<tt><a href='#ptype'>%type</a></tt> directive.</p>
<a name='destructor'></a>
<h4>The <tt>%destructor</tt> directive</h4>
-<p>The %destructor directive is used to specify a destructor for
+<p>The <tt>%destructor</tt> directive is used to specify a destructor for
a non-terminal symbol.
-(See also the <a href='#token_destructor'>%token_destructor</a>
+(See also the <tt><a href='#token_destructor'>%token_destructor</a></tt>
directive which is used to specify a destructor for terminal symbols.)</p>
<p>A non-terminal's destructor is called to dispose of the
%destructor nt { free($$); }
nt(A) ::= ID NUM. { A = malloc( 100 ); }
</pre>
-This example is a bit contrived but it serves to illustrate how
+This example is a bit contrived, but it serves to illustrate how
destructors work. The example shows a non-terminal named
"nt" that holds values of type "void*". When the rule for
an "nt" reduces, it sets the value of the non-terminal to
the non-terminal is used by C-code, then it is assumed that the
C-code will take care of destroying it.
More commonly, the value is used to build some
-larger structure and we don't want to destroy it, which is why
+larger structure, and we don't want to destroy it, which is why
the destructor is not called in this circumstance.</p>
<p>Destructors help avoid memory leaks by automatically freeing
allocated objects when they go out of scope.
To do the same using yacc or bison is much more difficult.</p>
-<a name="extraarg"></a>
+<a name='extraarg'></a>
<h4>The <tt>%extra_argument</tt> directive</h4>
-The %extra_argument directive instructs Lemon to add a 4th parameter
+The <tt>%extra_argument</tt> directive instructs Lemon to add a 4th parameter
to the parameter list of the Parse() function it generates. Lemon
doesn't do anything itself with this extra argument, but it does
make the argument available to C-code action routines, destructors,
<a name='pfallback'></a>
<h4>The <tt>%fallback</tt> directive</h4>
-<p>The %fallback directive specifies an alternative meaning for one
+<p>The <tt>%fallback</tt> directive specifies an alternative meaning for one
or more tokens. The alternative meaning is tried if the original token
-would have generated a syntax error.
+would have generated a syntax error.</p>
-<p>The %fallback directive was added to support robust parsing of SQL
-syntax in <a href="https://www.sqlite.org/">SQLite</a>.
+<p>The <tt>%fallback</tt> directive was added to support robust parsing of SQL
+syntax in <a href='https://www.sqlite.org/'>SQLite</a>.
The SQL language contains a large assortment of keywords, each of which
appears as a different token to the language parser. SQL contains so
-many keywords, that it can be difficult for programmers to keep up with
+many keywords that it can be difficult for programmers to keep up with
them all. Programmers will, therefore, sometimes mistakenly use an
-obscure language keyword for an identifier. The %fallback directive
+obscure language keyword for an identifier. The <tt>%fallback</tt> directive
provides a mechanism to tell the parser: "If you are unable to parse
-this keyword, try treating it as an identifier instead."
+this keyword, try treating it as an identifier instead."</p>
-<p>The syntax of %fallback is as follows:
+<p>The syntax of <tt>%fallback</tt> is as follows:
<blockquote>
-<tt>%fallback</tt> <i>ID</i> <i>TOKEN...</i> <b>.</b>
-</blockquote>
+<tt>%fallback</tt> <i>ID</i> <i>TOKEN...</i> <b>.</b>
+</blockquote></p>
-<p>In words, the %fallback directive is followed by a list of token names
-terminated by a period. The first token name is the fallback token - the
+<p>In words, the <tt>%fallback</tt> directive is followed by a list of token
+names terminated by a period.
+The first token name is the fallback token — the
token to which all the other tokens fall back to. The second and subsequent
arguments are tokens which fall back to the token identified by the first
-argument.
+argument.</p>
<a name='pifdef'></a>
-<h4>The <tt>%ifdef</tt>, <tt>%ifndef</tt>, and <tt>%endif</tt> directives.</h4>
+<h4>The <tt>%ifdef</tt>, <tt>%ifndef</tt>, and <tt>%endif</tt> directives</h4>
-<p>The %ifdef, %ifndef, and %endif directives are similar to
-#ifdef, #ifndef, and #endif in the C-preprocessor, just not as general.
+<p>The <tt>%ifdef</tt>, <tt>%ifndef</tt>, and <tt>%endif</tt> directives
+are similar to #ifdef, #ifndef, and #endif in the C-preprocessor,
+just not as general.
Each of these directives must begin at the left margin. No whitespace
-is allowed between the "%" and the directive name.
+is allowed between the "%" and the directive name.</p>
-<p>Grammar text in between "%ifdef MACRO" and the next nested "%endif" is
+<p>Grammar text in between "<tt>%ifdef MACRO</tt>" and the next nested
+"<tt>%endif</tt>" is
ignored unless the "-DMACRO" command-line option is used. Grammar text
-betwen "%ifndef MACRO" and the next nested "%endif" is included except when
-the "-DMACRO" command-line option is used.
+betwen "<tt>%ifndef MACRO</tt>" and the next nested "<tt>%endif</tt>" is
+included except when the "-DMACRO" command-line option is used.</p>
-<p>Note that the argument to %ifdef and %ifndef must be a single
-preprocessor symbol name, not a general expression. There is no "%else"
-directive.
+<p>Note that the argument to <tt>%ifdef</tt> and <tt>%ifndef</tt> must
+be a single preprocessor symbol name, not a general expression.
+There is no "<tt>%else</tt>" directive.</p>
<a name='pinclude'></a>
<h4>The <tt>%include</tt> directive</h4>
-<p>The %include directive specifies C code that is included at the
-top of the generated parser. You can include any text you want --
+<p>The <tt>%include</tt> directive specifies C code that is included at the
+top of the generated parser. You can include any text you want —
the Lemon parser generator copies it blindly. If you have multiple
-%include directives in your grammar file, their values are concatenated
-so that all %include code ultimately appears near the top of the
-generated parser, in the same order as it appeared in the grammer.</p>
+<tt>%include</tt> directives in your grammar file, their values are concatenated
+so that all <tt>%include</tt> code ultimately appears near the top of the
+generated parser, in the same order as it appeared in the grammar.</p>
-<p>The %include directive is very handy for getting some extra #include
+<p>The <tt>%include</tt> directive is very handy for getting some extra #include
preprocessor statements at the beginning of the generated parser.
For example:</p>
</pre></p>
<p>This might be needed, for example, if some of the C actions in the
-grammar call functions that are prototyed in unistd.h.</p>
+grammar call functions that are prototyped in unistd.h.</p>
<a name='pleft'></a>
<h4>The <tt>%left</tt> directive</h4>
-The %left directive is used (along with the <a href='#pright'>%right</a> and
-<a href='#pnonassoc'>%nonassoc</a> directives) to declare precedences of
-terminal symbols. Every terminal symbol whose name appears after
-a %left directive but before the next period (".") is
+The <tt>%left</tt> directive is used (along with the
+<tt><a href='#pright'>%right</a></tt> and
+<tt><a href='#pnonassoc'>%nonassoc</a></tt> directives) to declare
+precedences of terminal symbols.
+Every terminal symbol whose name appears after
+a <tt>%left</tt> directive but before the next period (".") is
given the same left-associative precedence value. Subsequent
-%left directives have higher precedence. For example:</p>
+<tt>%left</tt> directives have higher precedence. For example:</p>
<p><pre>
%left AND.
%right EXP NOT.
</pre></p>
-<p>Note the period that terminates each %left, %right or %nonassoc
+<p>Note the period that terminates each <tt>%left</tt>,
+<tt>%right</tt> or <tt>%nonassoc</tt>
directive.</p>
<p>LALR(1) grammars can get into a situation where they require
a large amount of stack space if you make heavy use or right-associative
-operators. For this reason, it is recommended that you use %left
-rather than %right whenever possible.</p>
+operators. For this reason, it is recommended that you use <tt>%left</tt>
+rather than <tt>%right</tt> whenever possible.</p>
<a name='pname'></a>
<h4>The <tt>%name</tt> directive</h4>
<p>By default, the functions generated by Lemon all begin with the
five-character string "Parse". You can change this string to something
-different using the %name directive. For instance:</p>
+different using the <tt>%name</tt> directive. For instance:</p>
<p><pre>
%name Abcde
<li> AbcdeTrace(), and
<li> Abcde().
</ul>
-The %name directive allows you to generator two or more different
-parsers and link them all into the same executable.
-</p>
+The <tt>%name</tt> directive allows you to generate two or more different
+parsers and link them all into the same executable.</p>
<a name='pnonassoc'></a>
<h4>The <tt>%nonassoc</tt> directive</h4>
<p>This directive is used to assign non-associative precedence to
-one or more terminal symbols. See the section on
+one or more terminal symbols. See the section on
<a href='#precrules'>precedence rules</a>
-or on the <a href='#pleft'>%left</a> directive for additional information.</p>
+or on the <tt><a href='#pleft'>%left</a></tt> directive
+for additional information.</p>
<a name='parse_accept'></a>
<h4>The <tt>%parse_accept</tt> directive</h4>
-<p>The %parse_accept directive specifies a block of C code that is
+<p>The <tt>%parse_accept</tt> directive specifies a block of C code that is
executed whenever the parser accepts its input string. To "accept"
an input string means that the parser was able to process all tokens
without error.</p>
<a name='parse_failure'></a>
<h4>The <tt>%parse_failure</tt> directive</h4>
-<p>The %parse_failure directive specifies a block of C code that
+<p>The <tt>%parse_failure</tt> directive specifies a block of C code that
is executed whenever the parser fails complete. This code is not
executed until the parser has tried and failed to resolve an input
error using is usual error recovery strategy. The routine is
<h4>The <tt>%right</tt> directive</h4>
<p>This directive is used to assign right-associative precedence to
-one or more terminal symbols. See the section on
+one or more terminal symbols. See the section on
<a href='#precrules'>precedence rules</a>
or on the <a href='#pleft'>%left</a> directive for additional information.</p>
<a name='stack_overflow'></a>
<h4>The <tt>%stack_overflow</tt> directive</h4>
-<p>The %stack_overflow directive specifies a block of C code that
+<p>The <tt>%stack_overflow</tt> directive specifies a block of C code that
is executed if the parser's internal stack ever overflows. Typically
this just prints an error message. After a stack overflow, the parser
will be unable to continue and must be reset.</p>
<p>You can help prevent parser stack overflows by avoiding the use
of right recursion and right-precedence operators in your grammar.
-Use left recursion and and left-precedence operators instead, to
+Use left recursion and and left-precedence operators instead to
encourage rules to reduce sooner and keep the stack size down.
For example, do rules like this:
<pre>
<pre>
list ::= element list. // right-recursion. Bad!
list ::= .
-</pre>
+</pre></p>
<a name='stack_size'></a>
<h4>The <tt>%stack_size</tt> directive</h4>
<p>If stack overflow is a problem and you can't resolve the trouble
by using left-recursion, then you might want to increase the size
of the parser's stack using this directive. Put an positive integer
-after the %stack_size directive and Lemon will generate a parse
+after the <tt>%stack_size</tt> directive and Lemon will generate a parse
with a stack of the requested size. The default value is 100.</p>
<p><pre>
<a name='start_symbol'></a>
<h4>The <tt>%start_symbol</tt> directive</h4>
-<p>By default, the start-symbol for the grammar that Lemon generates
+<p>By default, the start symbol for the grammar that Lemon generates
is the first non-terminal that appears in the grammar file. But you
-can choose a different start-symbol using the %start_symbol directive.</p>
+can choose a different start symbol using the
+<tt>%start_symbol</tt> directive.</p>
<p><pre>
%start_symbol prog
</pre></p>
+<a name='syntax_error'></a>
+<h4>The <tt>%syntax_error</tt> directive</h4>
+
+<p>See <a href='#error_processing'>Error Processing</a>.</p>
+
+<a name='token_class'></a>
+<h4>The <tt>%token_class</tt> directive</h4>
+
+<p>Undocumented. Appears to be related to the MULTITERMINAL concept.
+<a href='http://sqlite.org/src/fdiff?v1=796930d5fc2036c7&v2=624b24c5dc048e09&sbs=0'>Implementation</a>.</p>
+
<a name='token_destructor'></a>
<h4>The <tt>%token_destructor</tt> directive</h4>
-<p>The %destructor directive assigns a destructor to a non-terminal
-symbol. (See the description of the %destructor directive above.)
-This directive does the same thing for all terminal symbols.</p>
+<p>The <tt>%destructor</tt> directive assigns a destructor to a non-terminal
+symbol. (See the description of the
+<tt><a href='%destructor'>%destructor</a></tt> directive above.)
+The <tt>%token_destructor</tt> directive does the same thing
+for all terminal symbols.</p>
<p>Unlike non-terminal symbols which may each have a different data type
for their values, terminals all use the same data type (defined by
-the %token_type directive) and so they use a common destructor. Other
-than that, the token destructor works just like the non-terminal
+the <tt><a href='#token_type'>%token_type</a></tt> directive)
+and so they use a common destructor.
+Other than that, the token destructor works just like the non-terminal
destructors.</p>
<a name='token_prefix'></a>
<p>Lemon generates #defines that assign small integer constants
to each terminal symbol in the grammar. If desired, Lemon will
add a prefix specified by this directive
-to each of the #defines it generates.
-So if the default output of Lemon looked like this:
+to each of the #defines it generates.</p>
+
+<p>So if the default output of Lemon looked like this:
<pre>
#define AND 1
#define MINUS 2
#define TOKEN_MINUS 2
#define TOKEN_OR 3
#define TOKEN_PLUS 4
-</pre>
+</pre></p>
<a name='token_type'></a><a name='ptype'></a>
<h4>The <tt>%token_type</tt> and <tt>%type</tt> directives</h4>
is "void*".</p>
<p>Non-terminal symbols can each have their own data types. Typically
-the data type of a non-terminal is a pointer to the root of a parse-tree
+the data type of a non-terminal is a pointer to the root of a parse tree
structure that contains all information about that non-terminal.
For example:</p>
<a name='pwildcard'></a>
<h4>The <tt>%wildcard</tt> directive</h4>
-<p>The %wildcard directive is followed by a single token name and a
-period. This directive specifies that the identified token should
-match any input token.
+<p>The <tt>%wildcard</tt> directive is followed by a single token name and a
+period. This directive specifies that the identified token should
+match any input token.</p>
<p>When the generated parser has the choice of matching an input against
the wildcard token and some other token, the other token is always used.
-The wildcard token is only matched if there are no other alternatives.
+The wildcard token is only matched if there are no alternatives.</p>
+<a name='error_processing'></a>
<h3>Error Processing</h3>
<p>After extensive experimentation over several years, it has been
as good as it gets. And so that is what Lemon uses.</p>
<p>When a Lemon-generated parser encounters a syntax error, it
-first invokes the code specified by the %syntax_error directive, if
+first invokes the code specified by the <tt>%syntax_error</tt> directive, if
any. It then enters its error recovery strategy. The error recovery
strategy is to begin popping the parsers stack until it enters a
state where it is permitted to shift a special non-terminal symbol
named "error". It then shifts this non-terminal and continues
-parsing. But the %syntax_error routine will not be called again
+parsing. The <tt>%syntax_error</tt> routine will not be called again
until at least three new tokens have been successfully shifted.</p>
<p>If the parser pops its stack until the stack is empty, and it still
-is unable to shift the error symbol, then the %parse_failed routine
+is unable to shift the error symbol, then the
+<tt><a href='#parse_failure'>%parse_failure</a></tt> routine
is invoked and the parser resets itself to its start state, ready
to begin parsing a new file. This is what will happen at the very
-first syntax error, of course, if there are no instances of the
+first syntax error, of course, if there are no instances of the
"error" non-terminal in your grammar.</p>
</body>
projects / thirdparty / sqlite.git / commitdiff
