From: drh Date: Sat, 19 Mar 2016 18:00:44 +0000 (+0000) Subject: Updates to the Lemon documentation. X-Git-Tag: version-3.12.0~33 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=9bccde3d03a75ca4730b7c4dfc83c69a4b86b0fb;p=thirdparty%2Fsqlite.git Updates to the Lemon documentation. FossilOrigin-Name: f095341471aa822e6d556cb65512ec081c3918da --- diff --git a/doc/lemon.html b/doc/lemon.html index 2b8c613640..773c68e6ad 100644 --- a/doc/lemon.html +++ b/doc/lemon.html @@ -5,14 +5,17 @@

The Lemon Parser Generator

-

Lemon is an LALR(1) parser generator for C or C++. -It does the same job as ``bison'' and ``yacc''. -But lemon is not another bison or yacc clone. It +

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 uses a different grammar syntax which is designed to -reduce the number of coding errors. Lemon also uses a more -sophisticated parsing engine that is faster than yacc and -bison and which is both reentrant and thread-safe. -Furthermore, Lemon implements features that can be used +reduce the number of coding errors. Lemon also uses a +parsing engine that is faster than yacc and +bison and which is both reentrant and threadsafe. +(Update: Since the previous sentence was written, bison +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 in long-running programs such as graphical user interfaces or embedded controllers.

@@ -44,18 +47,18 @@ one and three files of outputs. automaton. By default, all three of these output files are generated. -The header file is suppressed if the ``-m'' command-line option is -used and the report file is omitted when ``-q'' is selected.

+The header file is suppressed if the "-m" command-line option is +used and the report file is omitted when "-q" is selected.

-

The grammar specification file uses a ``.y'' suffix, by convention. +

The grammar specification file uses a ".y" suffix, by convention. In the examples used in this document, we'll assume the name of the -grammar file is ``gram.y''. A typical use of Lemon would be the +grammar file is "gram.y". A typical use of Lemon would be the following command: 

    lemon gram.y
-This command will generate three output files named ``gram.c'', -``gram.h'' and ``gram.out''. +This command will generate three output files named "gram.c", +"gram.h" and "gram.out". The first is C code to implement the parser. The second is the header file that defines numerical values for all terminal symbols, and the last is the report that explains @@ -71,39 +74,35 @@ with a brief explanation of what each does by typing As of this writing, the following command-line options are supported: -The ``-b'' option reduces the amount of text in the report file by -printing only the basis of each parser state, rather than the full -configuration. -The ``-c'' option suppresses action table compression. Using -c -will make the parser a little larger and slower but it will detect -syntax errors sooner. -The ``-g'' option causes no output files to be generated at all. -Instead, the input grammar file is printed on standard output but -with all comments, actions and other extraneous text deleted. This -is a useful way to get a quick summary of a grammar. -The ``-m'' option causes the output C source file to be compatible -with the ``makeheaders'' program. -Makeheaders is a program that automatically generates header files -from C source code. When the ``-m'' option is used, the header -file is not output since the makeheaders program will take care -of generated all header files automatically. -The ``-q'' option suppresses the report file. -Using ``-s'' causes a brief summary of parser statistics to be -printed. Like this: -
-   Parser statistics: 74 terminals, 70 nonterminals, 179 rules
-                      340 states, 2026 parser table entries, 0 conflicts
-
-Finally, the ``-x'' option causes Lemon to print its version number -and then stops without attempting to read the grammar or generate a parser.

The Parser Interface

@@ -121,12 +120,12 @@ A new parser is created as follows: The ParseAlloc() routine allocates and initializes a new parser and returns a pointer to it. -The actual data structure used to represent a parser is opaque -- +The actual data structure used to represent a parser is opaque — its internal structure is not visible or usable by the calling routine. For this reason, the ParseAlloc() routine returns a pointer to void rather than a pointer to some particular structure. The sole argument to the ParseAlloc() routine is a pointer to the -subroutine used to allocate memory. Typically this means ``malloc()''.

+subroutine used to allocate memory. Typically this means malloc().

After a program is finished using a parser, it can reclaim all memory allocated by that parser by calling @@ -151,13 +150,13 @@ 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 map symbolic terminal symbol names into appropriate integer values. -(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.) +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 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 +such as "identifier" or "number" and the third argument will be the name of the identifier or the value of the number.

The Parse() function may have either three or four arguments, @@ -193,7 +192,7 @@ following: This example shows a user-written routine that parses a file of text and returns a pointer to the parse tree. -(We've omitted all error-handling from this example to keep it +(All error-handling code is omitted from this example to keep it simple.) We assume the existence of some kind of tokenizer which is created using TokenizerCreate() on line 8 and deleted by TokenizerFree() @@ -287,7 +286,7 @@ tokens) and it honors the same commenting conventions as C and C++.

Terminals and Nonterminals

A terminal symbol (token) is any string of alphanumeric -and underscore characters +and/or underscore characters that begins with an upper case letter. A terminal can contain lowercase letters after the first character, but the usual convention is to make terminals all upper case. @@ -314,7 +313,7 @@ must have alphanumeric names.

The main component of a Lemon grammar file is a sequence of grammar rules. Each grammar rule consists of a nonterminal symbol followed by -the special symbol ``::='' and then a list of terminals and/or nonterminals. +the special symbol "::=" and then a list of terminals and/or nonterminals. The rule is terminated by a period. The list of terminals and nonterminals on the right-hand side of the rule can be empty. @@ -330,9 +329,9 @@ A typical sequence of grammar rules might look something like this:

-

There is one non-terminal in this example, ``expr'', and five -terminal symbols or tokens: ``PLUS'', ``TIMES'', ``LPAREN'', -``RPAREN'' and ``VALUE''.

+

There is one non-terminal in this example, "expr", and five +terminal symbols or tokens: "PLUS", "TIMES", "LPAREN", +"RPAREN" and "VALUE".

Like yacc and bison, Lemon allows the grammar to specify a block of C code that will be executed whenever a grammar rule is reduced @@ -348,15 +347,15 @@ For example:

In order to be useful, grammar actions must normally be linked to their associated grammar rules. -In yacc and bison, this is accomplished by embedding a ``$$'' in the +In yacc and bison, this is accomplished by embedding a "$$" in the action to stand for the value of the left-hand side of the rule and -symbols ``$1'', ``$2'', and so forth to stand for the value of +symbols "$1", "$2", and so forth to stand for the value of the terminal or nonterminal at position 1, 2 and so forth on the right-hand side of the rule. This idea is very powerful, but it is also very error-prone. The single most common source of errors in a yacc or bison grammar is to miscount the number of symbols on the right-hand side of a grammar -rule and say ``$7'' when you really mean ``$8''.

+rule and say "$7" when you really mean "$8".

Lemon avoids the need to count grammar symbols by assigning symbolic names to each symbol in a grammar rule and then using those symbolic @@ -386,7 +385,7 @@ For example, the rule 

   expr(A) ::= expr(B) PLUS expr(C).  { A = B; }
-will generate an error because the linking symbol ``C'' is used +will generate an error because the linking symbol "C" is used in the grammar rule but not in the reduce action.

The Lemon notation for linking grammar rules to reduce actions @@ -394,6 +393,7 @@ also facilitates the use of destructors for reclaiming memory allocated by the values of terminals and nonterminals on the right-hand side of a rule.

+

Precedence Rules

Lemon resolves parsing ambiguities in exactly the same way as @@ -405,7 +405,10 @@ whichever rule comes first in the grammar file.

yacc and bison, Lemon allows a measure of control over the resolution of paring conflicts using precedence rules. A precedence value can be assigned to any terminal symbol -using the %left, %right or %nonassoc directives. Terminal symbols +using the +%left, +%right or +%nonassoc directives. Terminal symbols mentioned in earlier directives have a lower precedence that terminal symbols mentioned in later directives. For example:

@@ -525,7 +528,11 @@ other than that, the order of directives in Lemon is arbitrary.

  • %default_destructor
  • %default_type
  • %destructor +
  • %endif
  • %extra_argument +
  • %fallback +
  • %ifdef +
  • %ifndef
  • %include
  • %left
  • %name @@ -537,49 +544,57 @@ other than that, the order of directives in Lemon is arbitrary.

  • %stack_size
  • %start_symbol
  • %syntax_error +
  • %token_class
  • %token_destructor
  • %token_prefix
  • %token_type
  • %type +
  • %wildcard Each of these directives will be described separately in the following sections:

    +

    The %code directive

    -

    The %code directive is used to specify addition C/C++ code that +

    The %code directive is used to specify addition C code that is added to the end of the main output file. This is similar to -the %include directive except that %include is inserted at the -beginning of the main output file.

    +the %include directive except that %include +is inserted at the beginning of the main output file.

    %code is typically used to include some action routines or perhaps -a tokenizer as part of the output file.

    +a tokenizer or even the "main()" function +as part of the output file.

    +

    The %default_destructor directive

    The %default_destructor 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 %destructor directive below for additional information.

    +on the %destructor directive below for +additional information.

    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 non-terminals using a single statement.

    +

    The %default_type directive

    The %default_type directive specifies the datatype of non-terminal symbols that do no have their own datatype defined using a separate -%type directive. See the documentation on %type below for addition -information.

    +%type directive. +

    +

    The %destructor directive

    The %destructor directive is used to specify a destructor for a non-terminal symbol. -(See also the %token_destructor directive which is used to -specify a destructor for terminal symbols.)

    +(See also the %token_destructor +directive which is used to specify a destructor for terminal symbols.)

    A non-terminal's destructor is called to dispose of the non-terminal's value whenever the non-terminal is popped from @@ -602,26 +617,25 @@ or other resources held by that non-terminal.

    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 +"nt" that holds values of type "void*". When the rule for +an "nt" reduces, it sets the value of the non-terminal to space obtained from malloc(). Later, when the nt non-terminal is popped from the stack, the destructor will fire and call free() on this malloced space, thus avoiding a memory leak. -(Note that the symbol ``$$'' in the destructor code is replaced +(Note that the symbol "$$" in the destructor code is replaced by the value of the non-terminal.)

    It is important to note that the value of a non-terminal is passed to the destructor whenever the non-terminal is removed from the stack, unless the non-terminal is used in a C-code action. If the non-terminal is used by C-code, then it is assumed that the -C-code will take care of destroying it if it should really -be destroyed. More commonly, the value is used to build some +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 the destructor is not called in this circumstance.

    -

    By appropriate use of destructors, it is possible to -build a parser using Lemon that can be used within a long-running -program, such as a GUI, that will not leak memory or other resources. +

    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.

    @@ -638,17 +652,66 @@ and so forth. For example, if the grammar file contains:

    Then the Parse() function generated will have an 4th parameter -of type ``MyStruct*'' and all action routines will have access to -a variable named ``pAbc'' that is the value of the 4th parameter +of type "MyStruct*" and all action routines will have access to +a variable named "pAbc" that is the value of the 4th parameter in the most recent call to Parse().

    + +

    The %fallback directive

    + +

    The %fallback 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. + +

    The %fallback directive was added to support robust parsing of SQL +syntax in SQLite. +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 +them all. Programmers will, therefore, sometimes mistakenly use an +obscure language keyword for an identifier. The %fallback directive +provides a mechanism to tell the parser: "If you are unable to parse +this keyword, try treating it as an identifier instead." + +

    The syntax of %fallback is as follows: + +

    +%fallback ID TOKEN... . +
    + +

    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 +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. + + +

    The %ifdef, %ifndef, and %endif directives.

    + +

    The %ifdef, %ifndef, and %endif 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. + +

    Grammar text in between "%ifdef MACRO" and the next nested "%endif" 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. + +

    Note that the argument to %ifdef and %ifndef must be a single +preprocessor symbol name, not a general expression. There is no "%else" +directive. + + +

    The %include directive

    The %include 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 the value of the last -%include directive overwrites all the others.

    The %include directive is very handy for getting some extra #include preprocessor statements at the beginning of the generated parser. @@ -661,12 +724,13 @@ For example:

    This might be needed, for example, if some of the C actions in the grammar call functions that are prototyed in unistd.h.

    +

    The %left directive

    -The %left directive is used (along with the %right and -%nonassoc directives) to declare precedences of terminal -symbols. Every terminal symbol whose name appears after -a %left directive but before the next period (``.'') is +The %left directive is used (along with the %right and +%nonassoc directives) to declare precedences of +terminal symbols. Every terminal symbol whose name appears after +a %left directive but before the next period (".") is given the same left-associative precedence value. Subsequent %left directives have higher precedence. For example:

    @@ -687,10 +751,11 @@ 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.

    +

    The %name directive

    By default, the functions generated by Lemon all begin with the -five-character string ``Parse''. You can change this string to something +five-character string "Parse". You can change this string to something different using the %name directive. For instance:

    @@ -709,16 +774,19 @@ The %name directive allows you to generator two or more different
 parsers and link them all into the same executable.
 
    
 
+
 
    The %nonassoc directive
    
 
 
    This directive is used to assign non-associative precedence to
-one or more terminal symbols.  See the section on precedence rules
-or on the %left directive for additional information.
    
+one or more terminal symbols.  See the section on 
+precedence rules
+or on the %left directive for additional information.
    
 
+
 
    The %parse_accept directive
    
 
 
    The %parse_accept directive specifies a block of C code that is
-executed whenever the parser accepts its input string.  To ``accept''
+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.
    
 
@@ -730,7 +798,7 @@ without error.
    
    }

    - +

    The %parse_failure directive

    The %parse_failure directive specifies a block of C code that @@ -745,12 +813,15 @@ only invoked when parsing is unable to continue.

    }

    +

    The %right directive

    This directive is used to assign right-associative precedence to -one or more terminal symbols. See the section on precedence rules -or on the %left directive for additional information.

    +one or more terminal symbols. See the section on +precedence rules +or on the %left directive for additional information.

    +

    The %stack_overflow directive

    The %stack_overflow directive specifies a block of C code that @@ -779,6 +850,7 @@ Not like this: list ::= . +

    The %stack_size directive

    If stack overflow is a problem and you can't resolve the trouble @@ -791,6 +863,7 @@ with a stack of the requested size. The default value is 100.

    %stack_size 2000

    +

    The %start_symbol directive

    By default, the start-symbol for the grammar that Lemon generates @@ -801,6 +874,7 @@ can choose a different start-symbol using the %start_symbol directive.

    %start_symbol prog

    +

    The %token_destructor directive

    The %destructor directive assigns a destructor to a non-terminal @@ -813,6 +887,7 @@ the %token_type directive) and so they use a common destructor. Other than that, the token destructor works just like the non-terminal destructors.

    +

    The %token_prefix directive

    Lemon generates #defines that assign small integer constants @@ -838,6 +913,7 @@ to cause Lemon to produce these symbols instead: #define TOKEN_PLUS 4 +

    The %token_type and %type directives

    These directives are used to specify the data types for values @@ -853,7 +929,7 @@ token structure. Like this:

    If the data type of terminals is not specified, the default value -is ``int''.

    +is "int".

    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 @@ -874,6 +950,17 @@ non-terminal whose data type requires 1K of storage, then your 100 entry parser stack will require 100K of heap space. If you are willing and able to pay that price, fine. You just need to know.

    + +

    The %wildcard directive

    + +

    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. + +

    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. +

    Error Processing

    After extensive experimentation over several years, it has been @@ -885,7 +972,7 @@ first invokes the code specified by the %syntax_error 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 +named "error". It then shifts this non-terminal and continues parsing. But the %syntax_error routine will not be called again until at least three new tokens have been successfully shifted.

    @@ -894,7 +981,7 @@ is unable to shift the error symbol, then the %parse_failed 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 -``error'' non-terminal in your grammar.

    +"error" non-terminal in your grammar.

    diff --git a/manifest b/manifest index 16d972c4c4..0f76cddd77 100644 --- a/manifest +++ b/manifest @@ -1,5 +1,5 @@ -C Add\sthe\ssqlite3rbu_bp_progress()\sAPI\sto\sthe\sRBU\sextension.\sUsed\sto\sobtain\sthe\spercentage\sprogress\sof\san\sRBU\supdate. -D 2016-03-19T17:48:12.474 +C Updates\sto\sthe\sLemon\sdocumentation. +D 2016-03-19T18:00:44.390 F Makefile.in f53429fb2f313c099283659d0df6f20f932c861f F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434 F Makefile.msc df0bf9ff7f8b3f4dd9fb4cc43f92fe58f6ec5c66 @@ -33,7 +33,7 @@ F config.sub 9ebe4c3b3dab6431ece34f16828b594fb420da55 F configure c01a159fdf7ea0171ad01ce2937283f2c7972bde x F configure.ac 89e4e02a83d8a1528011f8395621b8c3186b4089 F contrib/sqlitecon.tcl 210a913ad63f9f991070821e599d600bd913e0ad -F doc/lemon.html c30255bea0fd87a81f082d17a72c9dffbc3f6dd9 +F doc/lemon.html e2118945e5f07ed146b45c9cd2b2dd6eabb8ebf2 F doc/pager-invariants.txt 27fed9a70ddad2088750c4a2b493b63853da2710 F doc/vfs-shm.txt e101f27ea02a8387ce46a05be2b1a902a021d37a F ext/README.txt 913a7bd3f4837ab14d7e063304181787658b14e1 @@ -1457,7 +1457,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0 -P 41c29c123ff347db720ed1a541c0b2ffc04670aa a1132dd9027d1c6dd845be307eeb38e535393f2c -R cb043230718add9f6d5b3a52d3cc19f9 -U dan -Z 67d28afde6e42b0d24beaa12aaf943b4 +P 209e31c729b9c8a09a80e43e3e4a2f3cd9384b3a +R fc92092a5d7485b32fa03b1aa106ab60 +U drh +Z 281323da864a48bf6b3196a4def3800c diff --git a/manifest.uuid b/manifest.uuid index 8119ca882f..e217909057 100644 --- a/manifest.uuid +++ b/manifest.uuid @@ -1 +1 @@ -209e31c729b9c8a09a80e43e3e4a2f3cd9384b3a \ No newline at end of file +f095341471aa822e6d556cb65512ec081c3918da \ No newline at end of file