简单的闭包运算(Closure)演示程序

 /*
  * 该程序用于计算某个产生式的闭包
  * RexfieldVon
  * 2013年8月9日16:01:38
  */
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

 #ifndef bool
 #    define bool char
 #endif

 #ifndef true
 #    define true
 #endif

 #ifndef false
 #    define false
 #endif

 struct Collection
 {
     char LeftUnterminal;        // 左非终结符
     char *Expression;            // 产生式
     char PreviewSymbol;            // 前瞻符号
     bool Processed;                // 是否被处理
     struct Collection *next;
 };
 /* 三级指针
  * 第一级指向整个产生式组
  * 第二级指向单个产生式
  * 第三级指向产生式符号单元
  * 约定：①所有的大写字母为非终结符②所有小写字母为终结符③'\377'为eof④'\0'为ε⑤'\376'为占位符·
  */
 char*** GrammerRule;
 /*
  * 文法书写约定：
  * 每个字符串表示一个单独的产生式
  * 第一个字符为产生式左边的非终结符，由初始化引擎进行产生式归并
  * 整个文法以 null 结束
  */
 char *Grammer[] =
 {
     "GL",
     "LLP", "LP",
     "P(P)", "P()",
     "\0"
 };
 /*
  * 初始化文法序列
  */
 void InitizationGrammerRule()
 {
     // 分配表头空间
     GrammerRule = (char***)malloc(sizeof(int) * );
     memset(GrammerRule, '\0', sizeof(int) * );
     // 扫描整个文法记录每个非终结符产生式的个数
     int UnterminalOp[], index;
     char Unterminal;
     memset(UnterminalOp, '\0',  * );
     for (index = ; (Unterminal = Grammer[index][]) != '\0'; index++)
     {
         UnterminalOp[Unterminal]++;
     }
     // 写入产生式
     for (index = ; (Unterminal = Grammer[index][]) != '\0'; index++)
     {
         if(GrammerRule[Unterminal] == NULL)
         {
             GrammerRule[Unterminal] = (char**)malloc(sizeof(int) * (UnterminalOp[Unterminal] + ));
             memset(GrammerRule[Unterminal], '\0', sizeof(int) * (UnterminalOp[Unterminal] + ));
         }
         // 找到空位
         int blank = ;
         while (GrammerRule[Unterminal][blank] != '\0') {blank++;}
         GrammerRule[Unterminal][blank] = &Grammer[index][];
     }
 }

 /*
  * 取得终结符数量
  * return 终结符的数量
  */
 int GetTerminalCount()
 {
     int i, TerminalCount = ;
     for (i = ; i < ; i++)
     {
         if (GrammerRule[i] != NULL)
         {
             int k = ;
             while (GrammerRule[i][k] != NULL)
             {
                 int n = ;
                 while (GrammerRule[i][k][n] != '\0')
                 {
                     char c = GrammerRule[i][k][n];
                     if (c < 'A' || c > 'Z')
                     {
                         TerminalCount++;
                     }
                     n++;
                 }
                 k++;
             }
         }
     }
     return TerminalCount;
 }

 /*
  * 递归取得 FIRST 集
  * Token : char 需要打印的符号
  * FIRST : char* FIRST集
  * Ptr : int* FIRST集的位置指针
  */
 void GetFIRST(char Token, char *FIRST, int *Ptr)
 {
     if (Token >= 'A' && Token <= 'Z' && GrammerRule[Token] != NULL)
     {
         int i = ;
         while (GrammerRule[Token][i] != NULL)
         {
             GetFIRST(GrammerRule[Token][i++][], FIRST, Ptr);
         }
     }
     else if (Token < 'A' || Token > 'Z')
     {
         FIRST[*Ptr] = Token;
         *Ptr = *Ptr + ;
     }
 }

 /*
  * 打印 LR(1) 项
  * Item : struct Collection* 需要打印的项
  */
 void PrintItem(struct Collection *Item)
 {
     printf("[%c ->", Item->LeftUnterminal);
     int i = ;
     for(; Item->Expression[i] != '\0'; i++)
     {
         printf(" ");
         switch (Item->Expression[i])
         {
             case '\377':
                 printf("<eof>");
                 break;
             case '\376':
                 printf("<@>");
                 break;
             default:
                 printf("%c", Item->Expression[i]);
                 break;
         }
     }
     if (Item->PreviewSymbol == '\377')
     {
         printf(", <eof>]\n");
     }
     else
     {
         printf(", %c]\n", Item->PreviewSymbol);
     }
 }

 /*
  * 添加项到集合
  * S : struct Collection* 项集
  * LeftUnterminal : char 左非终结符
  * Expression : char* 产生式
  * PreviewSymbol : char 前瞻符号
  */
 void AddItem(struct Collection *S, char LeftUnterminal, char *Expression, char PreviewSymbol)
 {
     static struct Collection *Tail = NULL;
     if (Tail == NULL) {Tail = S;}
     while (Tail->next != NULL) {Tail = Tail->next;}
     // 检查是否重复
     struct Collection *SPtr = S;
     for (; SPtr != NULL; SPtr = SPtr->next)
     {
         if (SPtr->LeftUnterminal == LeftUnterminal &&
             SPtr->PreviewSymbol == PreviewSymbol &&
             strcmp(SPtr->Expression, Expression) == )
         {
             return;
         }
     }
     struct Collection *NewItem = (struct Collection*)malloc(sizeof(struct Collection));
     NewItem->LeftUnterminal = LeftUnterminal;
     NewItem->Expression = strdup(Expression);
     NewItem->PreviewSymbol = PreviewSymbol;
     NewItem->next = NULL;
     NewItem->Processed = false;
     Tail->next = NewItem;
     Tail = Tail->next;
 }

 /*
  * 闭包运算
  * S : struct Collection* 项集
  * TerminalCount : int 终结符个数
  */
 void Closure(struct Collection *S, int TerminalCount)
 {
     bool CollectChanged;
     struct Collection *Ptr = S;
     do        // while (S is still changing)
     {
         CollectChanged = false;
         while (Ptr != NULL)        // for each item [A->β·Cζ，α]∈S
         {
             PrintItem(Ptr);
             char *Placeholder = strchr(Ptr->Expression, '\376');
             if (Placeholder != NULL && *(Placeholder + ) != '\0')        // 占位符不能在产生式尾
             {
                 char Unterminal = *(Placeholder + );
                 if (Unterminal >= 'A' && Unterminal <= 'Z')
                 {
                     int ProductionIndex;
                     for (ProductionIndex = ; GrammerRule[Unterminal][ProductionIndex] != NULL; ProductionIndex++)    // for each production C->γ∈P
                     {
                         char *FIRST = (char*)malloc(TerminalCount + ), FirstSymbol = *(Placeholder + );
                         FirstSymbol = (FirstSymbol != '\0')? FirstSymbol : Ptr->PreviewSymbol;
                         memset(FIRST, '\0', TerminalCount + );
                         int FIRSTCount = , i;
                         GetFIRST(FirstSymbol, FIRST, &FIRSTCount);
                         for (i = ; i < FIRSTCount; i++)        // for each b∈FIRST(ζα)
                         {
                             if (FIRST[i] != '\0')               // S <- S∪{[C->·γ,b]}
                             {
                                 char *Expr = (char*)malloc();
                                 Expr[] = '\376';
                                 Expr[] = '\0';
                                 Expr = strcat(Expr, GrammerRule[Unterminal][ProductionIndex]);
                                 AddItem(S, Unterminal, Expr, FIRST[i]);
                                 CollectChanged = true;
                             }
                         }
                     }
                 }
             }
             Ptr = Ptr->next;
         }
     }
     while (CollectChanged == true);
 }

 int main(int argc, char **argv)
 {
     InitizationGrammerRule();    // 初始化文法
     int TerminalCount = GetTerminalCount();
     struct Collection *S = (struct Collection*)malloc(sizeof(struct Collection));
     S->LeftUnterminal = 'G';
     S->Expression = "\376L";
     S->PreviewSymbol = '\377';
     S->next = NULL;
     S->Processed = false;
     Closure(S, TerminalCount);
     return ;
 }