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用YACC/LEX 设计计算机语言

發布時間：2025/6/15 编程问答 20 豆豆

生活随笔收集整理的這篇文章主要介紹了用YACC/LEX 设计计算机语言小編覺得挺不錯的,現在分享給大家,幫大家做個參考.

用YACC/LEX 設計計算機語言

前言：

YACC?（Yet Another Compiler Compiler）是1974年在?Unix?下設計出來的一個優秀的計算機語法分析工具。LEX?是相應的詞法分析工具。在?Linux?下，也有?YACC/LEX?的實現版本及相關資料。通過這套工具，可以在只編寫出計算機語言的語法后，就可以生成自底向上的語法分析程序（詞法分析類似），可以大大加快計算機語言的實現速度。

Turbo Pascal/Free Pascal/Delphi?程序員請注意：?Pascal?語言下的?YACC/LEX?實現可以在?http://www.musikwissenschaft.uni-mainz.de/~ag/tply/?地址下找到詳細信息。

有關YACC?和?LEX?的語法我們附在后面。這里，我們主要討論一個具體的語言（如?Basic），如何用?YACC/LEX?編程實現。代碼存放在下載欄目中（c語言，用GCC?編譯通過），可以任意使用，其它的源代碼和例子也可以在那里找到。

有關問題：

1、??首要問題：編譯還是解釋。如果選擇編譯，那么生成了目標機器上的可執行代碼。如果選擇解釋，那么在解釋過程中（或完成后）執行中間代碼。Java和.NET?已經混淆了這兩方面的區分。

2、??數據屬性問題：一個普通的編譯/解釋器必須隨時跟蹤變量、表達式的數據類型、作用范圍等問題。最頭疼的就是數據類型了。因為編譯/解釋器必須自己處理不同數據類型的轉換工作，如果有六種數據類型如?Char、Byte、SmallInt、Word、LongInt、Dword，就必須處理32種計算方法。所以現在新的的語言如（VBScript?等）都采用了?Variant?數據類型，這樣在計算過程中，不需要考慮過多的數據類型轉換問題，在執行時才做類型檢查。因為我們當時還不知道GCC的?Lib?中支持?Variant?數據類型，因此自己實現了Variant數據類型。

// Variant?數據類型
#define NOTYPE 0
#define CHARTYPE 1
#define BYTETYPE 2
#define INTEGERTYPE 3
#define DWORDTYPE 4
#define REALTYPE 5
#define STRINGTYPE 6
#define INFOTYPE 7
#define TMPSTRINGSIZE 128

/* Variant Structure */
typedef struct {
??????? int ValueType;
??????? union {
??????????????? Char Character;
??????????????? Byte BYTE;
??????????????? int Integer;
??????????????? DWord DWORD;
??????????????? double Real;
??????????????? PTString pString;
??????????????? void *pInfo;
??????? } Value;
} TVariant, *PVariant;

// Variant?過程
PVariant VarNew(void);
void VarFree(PVariant p);
int VarGetType(PVariant p);
void VarSetType(PVariant p,int tp);
void VarAssign(PVariant dest,PVariant src);
Char VarGetChar(PVariant p);
Byte VarGetByte(PVariant p);
int VarGetInteger(PVariant p);
DWord VarGetDWord(PVariant p);
double VarGetReal(PVariant p);
Char *VarGetString(PVariant p);
void *VarGetInfo(PVariant p);
void VarSetChar(PVariant p,Char c);
void VarSetByte(PVariant p,Byte b);
void VarSetInteger(PVariant p,int n);
void VarSetDWord(PVariant p,DWord d);
void VarSetReal(PVariant p,double e);
void VarSetString(PVariant p,Char *s);
void VarSetInfo(PVariant p,void *q);
int VarTypeCast(PVariant p,int datatype);
int VarMakeEqual(PVariant a,PVariant b);
void VarStrSetLength(PVariant p,DWord len);
void VarStrCompress(PVariant p);
DWord VarStrlen(PVariant p);
void VarStrToUpper(PVariant p);
void VarStrToLower(PVariant p);
int? VarStrCompare(PVariant p,PVariant q);
int VarStrCompareCase(PVariant p,PVariant q);
void VarStrAssign(PVariant dest,PVariant src);
void VarStrCat(PVariant dest,PVariant src);
void VarStrDelete(PVariant p,DWord begin,DWord len);
void VarStrGetChar(PVariant p,DWord offset);
void VarStrSetChar(PVariant p,DWord offset,Char c);
DWord VarStrLocChar(PVariant p,DWord begin,Char c);
DWord VarStrSubStr(PVariant p,PVariant sub);

3、??符號表：符號表用來登記各種常量、變量、函數、過程、結構的有關屬性，因為一些數據類型是其它數據類型的導出，所以這里采用二叉數存放、檢索信息。為了解決導出類型問題，此二叉數必須穿線。
typedef enum {
??????? eNoDefine,eConstDefine,eTypeDefine,eVarDefine,eValParamDefine,
??????? eVarParamDefine,eFieldDefine,
??????? eProgDefine,eFuncDefine,eProcDefine
} TDefineKey;
typedef enum {
??????? eDeclare,eForward,eStandard
} TRoutineKey;
typedef enum {
??????? eNoForm,eScalarForm,eEnumForm,eSubRangeForm,
??????? eArrayForm,eRecordForm
} TypeForm;
typedef struct {
??????? TDefineKey Key;
??????? union {
??????????????? PVariant pValue;?
??????????????? struct {
??????????????????????? TRoutineKey Key;
??????????????????????? int ParamCount;
??????????????????????? int TotalParamSize;
??????????????????????? int TotalLocalSize;
??????????????????????? struct tagTSymbolTable *Params;
??????????????????????? struct tagTSymbolTable *Locals;
??????????????????????? struct tagTSymbolTable *LocalSymtab;
??????????????????????? void *CodeSegment;
??????????????? } Routine;?
??????????????? struct {
??????????????????????? int Offset;
??????????????????????? struct tagTSymbolTable *RecordIDP;
??????????????? } Data;?
??????? }Info;
} TDefineStruct, *PDefineStruct;

typedef struct tagTypeStruct {
??????? TypeForm Form;
??????? int Size;
??????? struct tagTSymbolTable *TypeIDP;
??????? union {
??????????????? struct {
??????????????????????? struct TypeStruct *ConstIDP;
??????????????????????? int Max;
??????????????? } Enum;
??????????????? struct {
??????????????????????? struct tagTypeStruct *IndexType,*ElemType;
??????????????????????? int MinIndex,MaxIndex;
??????????????????????? int ElemCount;
??????????????? } Array;
??????????????? struct {
?????????????????????? struct tagTSymbolTable *FieldSymtab;
??????????????? } Record;
??????? } Info;
} TypeStruct, *PTypeStruct;

typedef struct tagTSymbolTable {
??????? char *Name;
??????? struct tagTSymbolTable *Left,*Right,*Next;? //?穿線二叉數
??????? char *Info;
??????? TDefineStruct Define;
??????? PTypeStruct TypeP;
??????? int Level;
??????? int LabelIndex;
} TSymbolTable, *PSymbolTable;

PSymbolTable NewSymtab(char *s);
void InitSymtabRoot(void);
extern TSymbolTable Root;
PSymbolTable SearchSymtab(char *s);
PSymbolTable EnterSymtab(char *s);
DWord GetVar(char *s);
void EnterVar(char *s,DWord index);

4、??虛擬計算機：如果生成的代碼目標平臺無法執行或執行有困難，可以考慮生成虛擬計算機的代碼，然后用自己的虛擬計算機執行。我們這里的虛擬計算機采用了棧結構方式。可以使?YACC?在分析過程中同步生成代碼。我們的虛擬機器代碼和JAVA很相似（JAVA在?SUN?中的實現，起初肯定是YACC）。這臺虛擬計算機連Print?命令都認識。

//?計算機的標志寄存器和控制寄存器
typedef struct tagTFlags {
??????? Char EQ,NE,LE,LT,GE,GT;
??????? Char Debug,Trace,Step;
} TFlags;
//?只有四個寄存器：當前代碼地址、堆棧頂部、Stack? Frame Top、標志及控制。
typedef struct tagTCPU {
??????? DWord EIP;
??????? DWord ESP;
??????? DWord EBP;
??????? TFlags Flags;
} TCPU, *PCPU;

//?全局的?CPU?變量
extern TCPU CPU;
// CPU?的動作
void Reset(void);
void Start(void);
void DeCode(DWord d);
void SetFlags(double r);
void Print(PVariant p);
void EnterProc(DWord n);?
void LeaveProc(void);

void PushChar(Char c);
void PushByte(Byte b);
void PushInteger(int value);
void PushDWord(DWord d);
void PushReal(double r);
void PushString(char *s);
void PushVar(PVariant p);
PVariant PopVar(void);
PVariant GetTosVar(void);

// CPU?認識的指令
#define C_PUSHCHAR 101
#define C_PUSHBYTE 102
#define C_PUSHINTEGER 103
#define C_PUSHDWORD 104
#define C_PUSHREAL 105
#define C_PUSHSTRING 106

#define C_PUSHVAR 110
#define C_POPVAR 120
#define C_POPCMP 121

#define C_RELOP 200
#define C_ADDOP 201
#define C_MULOP 202
#define C_SIGNOP 203

#define C_PRINT_LINE 300
#define C_PRINT_COMMA 301
#define C_PRINT_SEMICOLON 302
#define C_PRINT_EXPR 303

#define C_JMP 400
#define C_JEQ 401
#define C_JNE 402

5、??詞法分析：我們使用LEX來做詞法分析，查看LEX的代碼后發現，它本身是用YACC生成的，很有意思。

extern YYSTYPE yylval;

int yywrap(void) {
??????? return 1;
}

void SetReal(double r) {
??????? yylval.Real=r;
??????? yylval.Info.Type=REALTYPE;
}
void SetInteger(int n) {
??????? yylval.Integer=n;
??????? yylval.Info.Type=INTEGERTYPE;
}
void SetDWord(DWord n) {
??????? yylval.UnsignedNumber=n;
??????? yylval.Info.Type=DWORDTYPE;
}
void SetString(char *s) {
??????? yylval.String=strdup(s);
??????? yylval.Info.Type=STRINGTYPE;
}

/*???????? Delete any character in yyrval, normally is
??????? doublequota in string, etc:
??????? "AAAAA""aaaaaaa" =>? AAAAA"aaaaaaa
*/
void DeleteChar(char c) {
char *s;
int i,j;
??????? s=yylval.String;
??????? i=strlen(s);
??????? i-=2;
??????? memmove(s,s+1,sizeof(Char)*i);
??????? s[i]=0;
??????? if(strlen(s)<2)
??????????????? return;
??????? for(i=0,j=0;*(s+j);i++,j++) {
??????????????? *(s+i)=*(s+j);
??????????????? if((*(s+j)==c)&&(*(s+j+1)==c))
??????????????????????? j++;
??????? }
??????? *(s+i)=0;
}
%}
SPACE???????? [ \r\n\t\f]
NQUOTE???????? [^\"\n]
Digit??????? [0-9]
DecDigit [1-9]
Zero??????? [0]
OctDigit [0-7]
HexPrev??????? [x|X]
HexDigit [0-7A-Fa-f]
Char??????? [ -~]
Letter??????? [A-Za-z_]
Id??????? [A-Za-z0-9_]

%%
"=="??????? { SetInteger(EQUAL);return EQUAL; }
"="??????? { SetInteger(ASSIGN);return ASSIGN; }
"<"??????? { SetInteger(LT);return LT; }
"<="??????? { SetInteger(LE);return LE; }
"<>"??????? { SetInteger(NE);return NE; }
">="??????? { SetInteger(GE);return GE; }
">"??????? { SetInteger(GT);return GT; }
"+"??????? { SetInteger(PLUS);return PLUS; }
"-"??????? { SetInteger(MINUS);return MINUS; }
"*"??????? { SetInteger(STAR);return STAR; }
"/"??????? { SetInteger(SLASH);return SLASH; }
"%"??????? { SetInteger(MOD);return MOD; }
"<<"??????? { SetInteger(SHL);return SHL; }
">>"??????? { SetInteger(SHR);return SHR; }
"&"??????? { SetInteger(BITAND);return BITAND; }
"|"??????? { SetInteger(BITOR);return BITOR; }
"!"??????? { SetInteger(BITNOT);return BITNOT; }
"("??????? { SetInteger(LPAREN);return LPAREN; }
")"??????? { SetInteger(RPAREN);return RPAREN; }
"["??????? { SetInteger(LBRACKET);return LBRACKET; }
"]"??????? { SetInteger(RBRACKET);return RBRACKET; }
"{"??????? { SetInteger(BIGLPAREN);return BIGLPAREN; }
"}"??????? { SetInteger(BIGRPAREN); return BIGRPAREN; }
","??????? { SetInteger(COMMA);return COMMA; }
";"??????? { SetInteger(SEMICOLON);return SEMICOLON; }
":"??????? { SetInteger(COLON);return COLON; }
"."??????? { SetInteger(DOT);return DOT;}

"and"??????? { SetInteger(AND);return AND; }
"not"??????? { SetInteger(NOT);return NOT; }
"or"??????? { SetInteger(OR);return OR; }

"dim"??????? { SetInteger(DIM);return DIM; }
"array" { SetInteger(ARRAY);return ARRAY; }
"as"??????? { SetInteger(AS);return AS; }
"byval" { SetInteger(BYVAL);return BYVAL;}
"case"? { SetInteger(CASE);return CASE; }
"const" { SetInteger(CONST);return CONST; }
"function" { SetInteger(FUNCTION);return FUNCTION;}
"goto"? { SetInteger(GOTO);return GOTO;}
"label"??????? { SetInteger(LABEL);return LABEL;}
"procedure" { SetInteger(PROCEDURE);return PROCEDURE;}
"program" { SetInteger(PROGRAM);return PROGRAM; }

"char"????????? { SetInteger(CHAR);return CHAR; }
"byte"??? { SetInteger(BYTE);return BYTE; }
"integer" { SetInteger(INTEGER);return INTEGER; }
"dword"?? { SetInteger(DWORD);return DWORD; }
"real"????????? { SetInteger(REAL);return REAL; }
"string"? { SetInteger(STRING);return STRING; }

"if"??????? { SetInteger(IF);return IF; }
"then"??????? { SetInteger(THEN);return THEN; }
"else"??????? { SetInteger(ELSE);return ELSE; }
"for"???????? { SetInteger(FOR);return FOR; }
"while" { SetInteger(WHILE);return WHILE; }
"to"??????? { SetInteger(TO);return TO; }
"downto" { SetInteger(DOWNTO);return DOWNTO; }
"do"??????? { SetInteger(DO);return DO; }
"of"??????? { SetInteger(OF);return OF; }
"record" { SetInteger(RECORD);return RECORD; }
"with"? { SetInteger(WITH);return WITH;}

("quit"|"q")? { SetInteger(EXIT);return EXIT; }
("exit"|"e")? { SetInteger(EXIT);return EXIT; }
("print"|"?") {SetInteger(PRINT);return PRINT;}
"run"??????? { SetInteger(RUN);return RUN;}

{Letter}{Id}*??????????????????????? {
??????????????????????????????????????? /* ID */
??????????????????????????????????????? SetString(yytext);
??????????????????????????????????????? return ID;
??????????????????????????????? }
\"({NQUOTE}|\"\")*\"???????????????? {
??????????????????????????????????????? /* short string */
??????????????????????????????????????? SetString(yytext);
??????????????????????????????????????? DeleteChar('\"');
??????????????????????????????????????? return SHORTSTRING;
??????????????????????????????? }
{DecDigit}{Digit}*??????????????????????? {
??????????????????????????????????????? /* dec */
??????????????????????????????????????? SetDWord(strtoul(yytext,NULL,10));
??????????????????????????????????????? return(UNSIGNED_NUMBER);
??????????????????????????????? }
{Zero}{OctDigit}*??????????????? {??????? /* oct */
??????????????????????????????????????? SetDWord(strtoul(yytext,NULL,8));
??????????????????????????????????????? return(UNSIGNED_NUMBER);
??????????????????????????????? }
{Zero}{HexPrev}{HexDigit}+??????? {??????? /* hex */
??????????????????????????????????????? SetDWord(strtoul(yytext,NULL,16));
??????????????????????????????????????? return(UNSIGNED_NUMBER);
??????????????????????????????? }
{Digit}+"."{Digit}+??????????????? {
??????????????????????????????????????? /* float */
??????????????????????????????????????? SetReal(atof(yytext));
??????????????????????????????????????? return(REALNUMBER);
??????????????????????????????? }
{Digit}+"."{Digit}+[Ee][+-]?{Digit}+??????? {
??????????????????????????????????????? /* sce */
??????????????????????????????????????? SetReal(atof(yytext));
??????????????????????????????????????? return(REALNUMBER);
??????????????????????????????? }
"//".*??????????????????????????????? ;??????? { /* line comments */ }
{SPACE}??????????????????????????????? ;
.??????????????????????????????? |
%%

6、??語法分析：使用YACC來生成語法數。這里同時就生成了代碼，沒有考慮代碼優化的問題。

%{
%}
//?這是?Token?的數據結構
%Union {
??????? int Integer;
??????? DWord UnsignedNumber;
??????? double Real;
??????? Char *String;
??????? struct {
??????????????? double noused;
??????????????? int Type;
??????? } Info;
}

%token UNSIGNED_NUMBER REALNUMBER SHORTSTRING ID
%token LT LE EQUAL NE GE GT ASSIGN
%token PLUS MINUS STAR SLASH MOD SHL SHR BITNOT BITAND BITOR
%token LPAREN RPAREN OR AND NOT COMMA SEMICOLON COLON DOT
%token LBRACKET RBRACKET BIGLPAREN BIGRPAREN
%token DIM AS ARRAY CASE FUNCTION PROCEDURE PROGRAM LABEL
%token CHAR BYTE INTEGER DWORD REAL STRING
%token RECORD CONST BYVAL
%token IF THEN ELSE FOR TO DOWNTO DO WHILE OF GOTO WITH
%token EXIT PRINT RUN

%type <Real> REALNUMBER
%type <UnsignedNumber> UNSIGNED_NUMBER
%type <String> SHORTSTRING ID
%type <Integer> LT LE EQUAL NE GE GT ASSIGN
%type <Integer> PLUS MINUS STAR SLASH MOD SHL SHR BITNOT BITAND BITOR
%type <Integer> LPAREN RPAREN OR AND NOT COMMA SEMICOLON COLON DOT
%type <Integer> LBRACKET RBRACKET BIGLPAREN BIGRPAREN
%type <Integer> DIM AS ARRAY CASE FUNCTION PROCEDURE PROGRAM LABEL
%type <Integer> CHAR BYTE INTEGER DWORD REAL STRING
%type <Integer> IF THEN ELSE FOR TO DOWNTO WHILE OF GOTO WITH
%type <Integer> RECORD CONST BYVAL
%type <Integer> EXIT PRINT RUN

%type <Integer> relop addop mulop signop datatype logicop
%type <Integer> variable variable_list label
%type <Integer> primary factor term expression simple_expression expr expr_list
%type <Integer> compilation_unit program program_header block
%type <Integer> decl_sect_list decl_sect proc_decl func_decl param_list
%type <Integer> proc_header func_header proc_block fp_list fp_sect_list fp_sect
%type <Integer> compound_statement stmt_list stmt normal_stmt
%type <Integer> dim_statement goto_statement for_statement if_statement
%type <Integer> while_statement with_statement assign_statement proccall_statement
%type <Integer> run_statement
%type <Integer> print_statement print_expr_list print_dot
%right THEN ELSE??????? //?個別需要右結合的?Token

compilation_unit:program
;
program:program_header block
??????? ;
program_header: {}
??????? |PROGRAM
??????? |PROGRAM ID SEMICOLON
??????? ;
block??????? :decl_sect_list compound_statement
??????? ;
decl_sect_list: {}
??????? |decl_sect_list decl_sect
??????? ;
decl_sect:proc_decl
??????? |func_decl
??????? ;
proc_decl:proc_header proc_block
??????? ;
func_decl:func_header proc_block
??????? ;
proc_header:PROCEDURE ID fp_list
??????? ;
func_header:FUNCTION ID fp_list AS datatype
??????? ;
proc_block:block
??????? ;
fp_list:{}
??????? |LPAREN fp_sect_list RPAREN
??????? ;
fp_sect_list:fp_sect
??????? |fp_sect_list SEMICOLON fp_sect
??????? ;
fp_sect:variable_list AS datatype
??????? |BYVAL variable_list AS datatype
??????? ;
compound_statement:BIGLPAREN stmt_list BIGRPAREN
??????? ;
stmt_list:stmt
??????? |stmt_list SEMICOLON stmt
??????? ;
stmt:normal_stmt
??????? |label COLON normal_stmt
??????? ;
normal_stmt:{}??????? /* empty */
??????? |dim_statement
??????? |assign_statement
??????? |proccall_statement
??????? |goto_statement
??????? |compound_statement
??????? |if_statement
??????? |for_statement
??????? |while_statement
??????? |with_statement
??????? |print_statement
??????? |run_statement
??????? ;
run_statement:RUN {exec();}
??????? |EXIT {exit(0);}
print_statement:PRINT print_expr_list { WriteCode(C_PRINT_LINE); }
??????? ;
print_expr_list:expr { WriteCode(C_PRINT_EXPR);}
??????? |print_expr_list print_dot expr {WriteCode(C_PRINT_EXPR);}
??????? ;
print_dot:COMMA {WriteCode(C_PRINT_COMMA);}
??????? |COLON {WriteCode(C_PRINT_SEMICOLON);}
??????? ;
dim_statement:DIM variable AS datatype? {
PVariant p;
??????? p=GetData($2);
??????? VarSetType(p,$4);
}
??????? ;
assign_statement:variable ASSIGN expr {
??????? WriteCode2(C_POPVAR,$1);
}
??????? ;
proccall_statement:ID param_list {}
??????? ;
goto_statement:GOTO label {WriteCode2(C_JMP,$2);}
??????? ;
label??????? :ID {
DWord d;
??????? d=GetVar($1);
??????? if(d==OUTOFSTRINGINDEX) {
??????????????? d=GetIP();
??????????????? EnterVar($1,d);
??????? }
??????? $$=d;
}
??????? ;
if_statement:IF? expr {
??????? WriteCode(C_POPCMP);
??????? $2=GetIP();
??????? WriteCode2(C_JEQ,0);
} THEN stmt {
??????? SetCode($2+1,GetIP());
}
??????? ;
while_statement:WHILE {
??????? $1=GetIP();
} expr {
??????? WriteCode(C_POPCMP);
??????? $2=GetIP();
???????? WriteCode2(C_JEQ,0);
} DO stmt {
??????? WriteCode2(C_JMP,$1);
??????? SetCode($2+1,GetIP());
}
??????? ;
for_statement:FOR variable ASSIGN expr {
??????? $4=GetIP();
??????? WriteCode2(C_POPVAR,$2);
??????? WriteCode2(C_PUSHVAR,$2);
} TO expr {
??????? WriteCode2(C_RELOP,LE);
}
DO {
??????? WriteCode(C_POPCMP);
??????? $6=GetIP();
??????? WriteCode2(C_JEQ,0);
} stmt {
??????? WriteCode2(C_PUSHVAR,$2);
??????? WriteCode2(C_PUSHINTEGER,1);
??????? WriteCode2(C_ADDOP,PLUS);
??????? WriteCode2(C_JMP,$4);
??????? SetCode($6+1,GetIP());
}
??????? ;
with_statement:WITH variable DO stmt
??????? ;
param_list:??????? {}/* empty */
??????? |LPAREN expr_list RPAREN
??????? ;
expr_list:expr
??????? |expr_list COMMA expr
??????? ;
expr:simple_expression
??????? |NOT simple_expression
??????? |expr logicop simple_expression
??????? ;
simple_expression:expression
??????? |expression relop expression {WriteCode2(C_RELOP,$2);}
??????? ;
expression:term
??????? |expression addop term {WriteCode2(C_ADDOP,$2);}
??????? ;
term??????? :factor
??????? |term mulop factor? { WriteCode2(C_MULOP,$2);}
??????? |BITNOT factor
??????? ;
factor??????? :signop factor {WriteCode2(C_SIGNOP,$1);}
??????? |primary
??????? ;
primary??????? :variable {WriteCode2(C_PUSHVAR,$1);}
??????? |UNSIGNED_NUMBER {? WriteCode2(C_PUSHINTEGER,$1);}
??????? |REALNUMBER??????? {
??????? double r;
??????? DWord *d;
??????????????? WriteCode(C_PUSHREAL);
??????????????? r=$1;
??????????????? d=(DWord *)&r;
??????????????? WriteCode2(*d,*(d+1));
}
??????? |SHORTSTRING???????? {
??????? char *s;
??????????????? s=strdup($1);
??????????????? WriteCode(C_PUSHSTRING);
??????????????? WriteCode((DWord)s);
}
??????? |LPAREN expr RPAREN
??????? |ID LPAREN expr_list RPAREN {}???????? /* type cast, function call */
??????? ;
logicop :AND
??????? |OR
??????? ;
relop??????? :EQUAL
??????? |NE
??????? |LT
??????? |LE
??????? |GT
??????? |GE
??????? ;
addop??????? :PLUS
??????? |MINUS
??????? ;
mulop??????? :STAR
??????? |SLASH
??????? |MOD
??????? |SHL
??????? |SHR
??????? |BITAND
??????? |BITOR
??????? ;
signop??????? :addop
??????? ;
variable_list:variable
??????? |variable_list COMMA variable
??????? ;
variable:ID {
PSymbolTable q;
PVariant p;
DWord d;
??????? d=GetVar($1);
??????? if(d==OUTOFSTRINGINDEX) {
??????????????? d=GetFreeDIP();
??????????????? EnterVar($1,d);
??????????????? InitData(d,NOTYPE);
??????? }
??????? $$=d;
}
??????? |variable LBRACKET expr_list RBRACKET???????? /* array */
??????? |variable DOT ID??????????????????????? /* record */
??????? |variable '^'????????????????????????????????? /* pointer */
??????? |ID LPAREN variable RPAREN {}??????????????? /* type cast */
??????? ;
datatype:CHAR {$$=CHARTYPE;}
??????? |BYTE {$$=BYTETYPE;}
??????? |STRING {$$=STRINGTYPE;}
??????? |INTEGER {$$=INTEGERTYPE;}
??????? |DWORD {$$=DWORDTYPE;}
??????? |REAL {$$=REALTYPE;}
??????? ;
%%

void main() {
??????? InitSymtabRoot();
??????? ResetIP();
??????? yyparse();
??????? exec();
}
yyerror(char *s) {
??????? printf("Error> %s\n",s);
}
exec() {
?????? Reset();
??????? Start();
/*??????? ResetIP();*/
}
W(char *s) {
??????? printf("%s\n",s);
??????? fflush(stdout);
}
P(void) {
int i;
?????? for(i=0;i<GetIP();i++)
??????????????? printf("%d:%d? ",i,CodeSegment[i]);
}

7、??內存組織和代碼生成：我們的內存中有三個邏輯段：數據、堆棧、代碼，數據和堆棧共用同一個物理段，棧頂向下生長，代碼段單獨分開。在語法分析時，向內存中寫入指令和數據，在執行時，再讀出來。代碼生成時如果遇到不可知跳轉（如If、While、For等等），就使用預添0技術，先在這個位置填寫?Nop，在遇到語句結束后，知道了地址，再在這里添入要跳轉的代碼。需要注意的是數據/堆棧段的每個內存單元存儲的是指向?Variant?數據類型的指針（這臺虛擬計算機的每個內存單元都有四個字節大）。

#define MAXCODESEGMENTSIZE 65536
#define MAXDATASEGMENTSIZE 65536

extern DWord CodeSegment[MAXCODESEGMENTSIZE];
extern DWord sIP;
extern PVariant DataSegment[MAXDATASEGMENTSIZE];

void WriteCode(DWord c);
void WriteCode2(DWord c1,DWord c2);
void SetCode(DWord offset,DWord op);
DWord GetIP();
void SetIP(DWord ip);
DWord ReadCode();
void ResetIP(void);

DWord GetFreeDIP();
PVariant GetData(DWord offset);
void SetData(DWord offset,PVariant val);
void InitData(DWord offset,int datatype);
void FreeData(DWord offset);
void InitDataSegment(void);
void ReleaseDataSegment(void);

程序編譯及執行：
首先用?Lex?編譯?calc.l?生成lex.yy.c?，然后用?yacc?編譯?calc.y?生成?y.tab.h、y.tab.c和y.code.c?（如果你沒有修改，可省略）。
用?gcc?編譯所有c文件。
執行時缺省從?stdin?讀入，解釋完成后，如果沒有錯誤，就會執行看到結果，如果要執行文件，請使用重定向。

大家注意：我們的Basis語言更像Pascal語言。請看例子：

例一：
program aaa;
{
dim a as integer;
dim b as real;
dim c as string;

a=12;
b=a*2.2;
c="aaa";
c=c+a+b;
? a,b,c;
}

例二：
program aaa;
{
dim a as Integer;
dim b as Real;
dim ccc as string;
a=1;
a=a+1;
a=a*(a+20);
a=-a;
b=a;
b=b*2.71828;
ccc=ccc+"ASDF"" DED";
dim ddd as real;
ddd=0.123;
ddd=ddd*(ddd-2*ddd);
print a,b,ccc,ddd;
}

例三：
program aaa;
{
dim a as integer;
a=1;
while a<10? do {
??????? print a;
??????? a=a+1;
}
}

例四：
program t5;
{
dim a as integer;
a=1;
loop:
print a;
a=a+1;
if a<10 then goto loop;
print "Done";
}

例五：
program aaa;
{
dim a as integer;
for a=-2 to 2 do print a*a;
}

后記：

本來想詳細寫一下如何使用YACC，但我覺得這些應該是已經有的話題，所以這里將?TPLY 4.1?版本的幫助附在后面，它很詳細，我沒什么可補充的。

自從96.5?第一次遇到?Delphi 1.0?以后，我一直在?Delphi?下編寫程序。但我總覺得想做一個合格的?Delphi?程序員，也應該也從其它地方學習，才能有所進步。

????? TP Lex and Yacc - The Compiler Writer's Tools for Turbo Pascal

????? == === === ==== = === ======== ======== ===== === ===== ======

???????????????????? Version 4.1 User Manual

???????????????????? ======= === ==== ======

???????????????????????? Albert Graef

???????????????? Department of Musicinformatics

?????????????? Johannes Gutenberg-University Mainz

???????????????ag@muwiinfa.geschichte.uni-mainz.de

????????????????????????? April 1998

Introduction

============

This document describes the TP Lex and Yacc compiler generator toolset. These

tools are designed especially to help you prepare compilers and similar

programs like text processing utilities and command language interpreters with

the Turbo Pascal (TM) programming language.

TP Lex and Yacc are Turbo Pascal adaptions of the well-known UNIX (TM)

utilities Lex and Yacc, which were written by M.E. Lesk and S.C. Johnson at

Bell Laboratories, and are used with the C programming language. TP Lex and

Yacc are intended to be approximately "compatible" with these programs.

However, they are an independent development of the author, based on the

techniques described in the famous "dragon book" of Aho, Sethi and Ullman

(Aho, Sethi, Ullman: "Compilers : principles, techniques and tools," Reading

(Mass.), Addison-Wesley, 1986).

Version 4.1 of TP Lex and Yacc works with all recent flavours of Turbo/Borland

Pascal, including Delphi, and with the Free Pascal Compiler, a free Turbo

Pascal-compatible compiler which currently runs on DOS and Linux (other ports

are under development). Recent information about TP Lex/Yacc, and the sources

are available from the TPLY homepage:

???http://www.musikwissenschaft.uni-mainz.de/~ag/tply

For information about the Free Pascal Compiler, please refer to:

???http://www.freepascal.org

TP Lex and Yacc, like any other tools of this kind, are not intended for

novices or casual programmers; they require extensive programming experience

as well as a thorough understanding of the principles of parser design and

implementation to be put to work successfully. But if you are a seasoned Turbo

Pascal programmer with some background in compiler design and formal language

theory, you will almost certainly find TP Lex and Yacc to be a powerful

extension of your Turbo Pascal toolset.

This manual tells you how to get started with the TP Lex and Yacc programs and

provides a short description of these programs. Some knowledge about the C

versions of Lex and Yacc will be useful, although not strictly necessary. For

總結

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