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page-grammar_en_rdoc.ri
U:RDoc::TopLevel[ i I""lib/racc/rdoc/grammar.en.rdoc:ETcRDoc::Parser::Simpleo:RDoc::Markup::Document: @parts[vS:RDoc::Markup::Heading: leveli: textI" Racc Grammar File Reference;To: RDoc::Markup::BlankLine S; ; i; I"Global Structure;T@ S; ; i; I"$Class Block and User Code Block;T@ o: RDoc::Markup::Paragraph;[I"bThere are two blocks on the toplevel. One is the 'class' block, the other is the 'user code' ;TI"Iblock. The 'user code' block MUST be placed after the 'class' block.;T@ S; ; i; I" Comments;T@ o; ;[I"}You can insert comments about all places. Two styles of comments can be used, Ruby style '#.....' and C style '/\*......*\/'.;T@ S; ; i; I"Class Block;T@ o; ;[I")The class block is formed like this:;T@ o:RDoc::Markup::Verbatim;[I"class CLASS_NAME ;TI" [precedence table] ;TI" [token declarations] ;TI"* [expected number of S/R conflicts] ;TI" [options] ;TI"# [semantic value conversion] ;TI" [start rule] ;TI" rule ;TI" GRAMMARS ;T: @format0o; ;[I"YCLASS_NAME is a name of the parser class. This is the name of the generating parser ;TI" class.;T@ o; ;[I"WIf CLASS_NAME includes '::', Racc outputs the module clause. For example, writing ;TI"6"class M::C" causes the code below to be created:;T@ o;;[ I"module M ;TI" class C ;TI" : ;TI" : ;TI" end ;TI" end ;T;0S; ; i; I"Grammar Block;T@ o; ;[I"WThe grammar block describes grammar which is able to be understood by the parser. ;TI"Syntax is:;T@ o;;[ I"3(token): (token) (token) (token).... (action) ;TI" ;TI"3(token): (token) (token) (token).... (action) ;TI"3 | (token) (token) (token).... (action) ;TI"3 | (token) (token) (token).... (action) ;T;0o; ;[I"J(action) is an action which is executed when its (token)s are found. ;TI"B(action) is a ruby code block, which is surrounded by braces:;T@ o;;[I"{ print val[0] ;TI" puts val[1] } ;T;0o; ;[I"ONote that you cannot use '%' string, here document, '%r' regexp in action.;T@ o; ;[I"KActions can be omitted. When it is omitted, '' (empty string) is used.;T@ o; ;[I"]A return value of action is a value of the left side value ($$). It is the value of the ;TI"9result, or the returned value by `return` statement.;T@ o; ;[I"3Here is an example of the whole grammar block.;T@ o;;[I" rule ;TI"6 goal: definition rules source { result = val } ;TI" ;TI"0 definition: /* none */ { result = [] } ;TI"9 | definition startdesig { result[0] = val[1] } ;TI" | definition ;TI"C precrule # this line continues from upper line ;TI" { ;TI" result[1] = val[1] ;TI" } ;TI" ;TI" startdesig: START TOKEN ;T;0o; ;[I"AYou can use the following special local variables in action:;T@ o:RDoc::Markup::List: @type: BULLET: @items[o:RDoc::Markup::ListItem: @label0;[o; ;[I"result ($$);T@ o; ;[I"FThe value of the left-hand side (lhs). A default value is val[0].;T@ o;;;;[o;;0;[o; ;[I"val ($1,$2,$3...);T@ o; ;[I"4An array of value of the right-hand side (rhs).;T@ o;;;;[o;;0;[o; ;[I" _values (...$-2,$-1,$0);T@ o; ;[I"TA stack of values. DO NOT MODIFY this stack unless you know what you are doing.;T@ S; ; i; I"Operator Precedence;T@ o; ;[I"0This function is equal to '%prec' in yacc. ;TI" To designate this block:;T@ o;;[ I"prechigh ;TI" nonassoc '++' ;TI" left '*' '/' ;TI" left '+' '-' ;TI" right '=' ;TI" preclow ;T;0o; ;[I"6`right` is yacc's %right, `left` is yacc's %left.;T@ o; ;[I"'`=` + (symbol) means yacc's %prec:;T@ o;;[I"prechigh ;TI" nonassoc UMINUS ;TI" left '*' '/' ;TI" left '+' '-' ;TI" preclow ;TI" ;TI" rule ;TI" exp: exp '*' exp ;TI" | exp '-' exp ;TI"? | '-' exp =UMINUS # equals to "%prec UMINUS" ;TI" : ;TI" : ;T;0S; ; i; I" expect;T@ o; ;[I")Racc has bison's "expect" directive.;T@ o;;[ I"# Example ;TI" ;TI"class MyParser ;TI" rule ;TI" expect 3 ;TI" : ;TI" : ;T;0o; ;[I"MThis directive declares "expected" number of shift/reduce conflicts. If ;TI"Q"expected" number is equal to real number of conflicts, Racc does not print ;TI" conflict warning message.;T@ S; ; i; I"Declaring Tokens;T@ o; ;[I"QBy declaring tokens, you can avoid many meaningless bugs. If declared token ;TI"Pdoes not exist or existing token does not decleared, Racc output warnings. ;TI"Declaration syntax is:;T@ o;;[I""token TOKEN_NAME AND_IS_THIS ;TI"5 ALSO_THIS_IS AGAIN_AND_AGAIN THIS_IS_LAST ;T;0S; ; i; I" Options;T@ o; ;[I">You can write options for Racc command in your Racc file.;T@ o;;[I" options OPTION OPTION ... ;T;0o; ;[I"Options are:;T@ o;;;;[o;;0;[o; ;[I"omit_action_call;T@ o; ;[I"$omits empty action call or not.;T@ o;;;;[o;;0;[o; ;[I"result_var;T@ o; ;[I")uses local variable "result" or not.;T@ o; ;[I"7You can use 'no_' prefix to invert their meanings.;T@ S; ; i; I" Converting Token Symbol;T@ o; ;[I"#Token symbols are, as default,;T@ o;;[ I"H* naked token string in Racc file (TOK, XFILE, this_is_token, ...) ;TI"6 --> symbol (:TOK, :XFILE, :this_is_token, ...) ;TI"** quoted string (':', '.', '(', ...) ;TI", --> same string (':', '.', '(', ...) ;T;0o; ;[I"5You can change this default by "convert" block. ;TI"Here is an example:;T@ o;;[ I" convert ;TI"E PLUS 'PlusClass' # We use PlusClass for symbol of `PLUS' ;TI"E MIN 'MinusClass' # We use MinusClass for symbol of `MIN' ;TI" end ;T;0o; ;[I"CWe can use almost all ruby value can be used by token symbol, ;TI"Cexcept 'false' and 'nil'. These cause unexpected parse error.;T@ o; ;[I"JIf you want to use String as token symbol, special care is required. ;TI"For example:;T@ o;;[ I" convert ;TI"1 class '"cls"' # in code, "cls" ;TI"4 PLUS '"plus\n"' # in code, "plus\n" ;TI"; MIN "\"minus#{val}\"" # in code, \"minus#{val}\" ;TI" end ;T;0S; ; i; I"Start Rule;T@ o; ;[I"/'%start' in yacc. This changes start rule.;T@ o;;[I"start real_target ;T;0S; ; i; I"User Code Block;T@ o; ;[I"R"User Code Block" is a Ruby source code which is copied to output. There are ;TI";three user code blocks, "header" "inner" and "footer".;T@ o; ;[I"&Format of user code is like this:;T@ o;;[I"---- header ;TI" ruby statement ;TI" ruby statement ;TI" ruby statement ;TI" ;TI"---- inner ;TI" ruby statement ;TI" : ;TI" : ;T;0o; ;[I"PIf four '-' exist on the line head, Racc treats it as the beginning of the ;TI"Huser code block. The name of the user code block must be one word.;T: @file@:0@omit_headings_from_table_of_contents_below0