mglyac.y

《Lex与Yacc》中文第二版,附带书中的程序

%{
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
    
int screen_done = 1; /* 1 if done, 0 otherwise */
char *act_str;   /* extra argument for an action */
char *cmd_str;   /* extra argument for command */
char *item_str;  /* extra argument for 
                  * item description */
%}

%union {
    char    *string;     /* string buffer */
    int    cmd;          /* command value */
}

%token <string> QSTRING ID COMMENT 
%token <cmd> SCREEN TITLE ITEM COMMAND ACTION EXECUTE EMPTY
%token <cmd> MENU QUIT IGNORE ATTRIBUTE VISIBLE INVISIBLE END

%type <cmd> action line attribute command
%type <string> id qstring

%start screens

%%

screens:  screen
        | screens screen
        ;
screen:   screen_name screen_contents screen_terminator
        | screen_name screen_terminator
        ;

screen_name: SCREEN id { start_screen($2); }
           | SCREEN    { start_screen(strdup("default")); }
           ;
        
screen_terminator: END id { end_screen($2); }
                 | END { end_screen(strdup("default")); }
                 ;
            
screen_contents: titles lines
               ;

titles: /* empty */
      | titles title
      ;

title: TITLE qstring { add_title($2); }
     ;

lines: line
     | lines line
     ;

line: ITEM qstring command ACTION action attribute
         { item_str = $2;
	   add_line($5, $6);
           $$ = ITEM;
          }
        ;
        
command: /* empty */ { cmd_str = strdup(""); }
       | COMMAND id  { cmd_str = $2; }
        ;

action: EXECUTE qstring
         { act_str = $2;
	   $$ = EXECUTE;
         }
      | MENU id
         { /* make "menu_" $2 */
	   act_str = malloc(strlen($2) + 6);
	   strcpy(act_str,"menu_");
           strcat(act_str, $2);
	   free($2);
	   $$ = MENU;
	 }
      | QUIT   { $$ = QUIT; }
      | IGNORE { $$ = IGNORE; }
      ;
        
attribute: /* empty */     { $$ = VISIBLE; }
         | ATTRIBUTE VISIBLE { $$ = VISIBLE; }
         | ATTRIBUTE INVISIBLE { $$ = INVISIBLE; }
         ;
        
id: ID
     { $$ = $1; }
  | QSTRING
     { warning("String literal inappropriate",
               (char *)0);
       $$ = $1;	/* but use it anyway */
     }
  ;

qstring: QSTRING { $$ = $1; }
       | ID 
          { warning("Non-string literal inappropriate",
                    (char *)0);
	    $$ = $1;	/* but use it anyway */
          }
        ;
%%

char *progname = "mgl";
int lineno = 1;

#define DEFAULT_OUTFILE "screen.out"

char *usage = "%s: usage [infile] [outfile]\n";

main(int argc, char **argv)
{
	char *outfile;
	char *infile;
	extern FILE *yyin, *yyout;
    
	progname = argv[0];
    
	if(argc > 3)
	{
        	fprintf(stderr,usage, progname);
		exit(1);
	}
	if(argc > 1)
	{
		infile = argv[1];
		/* open for read */
		yyin = fopen(infile,"r");
		if(yyin == NULL) /* open failed */
		{
			fprintf(stderr,"%s: cannot open %s\n", 
				progname, infile);
			exit(1);
		}
	}

	if(argc > 2)
	{
		outfile = argv[2];
	}
	else
	{
      		outfile = DEFAULT_OUTFILE;
	}
    
	yyout = fopen(outfile,"w");
	if(yyout == NULL) /* open failed */
	{
      		fprintf(stderr,"%s: cannot open %s\n", 
                	progname, outfile);
		exit(1);
	}
    
	/* normal interaction on yyin and 
	   yyout from now on */
    
	yyparse();
    
	end_file(); /* write out any final information */
    
	/* now check EOF condition */
	if(!screen_done) /* in the middle of a screen */
	{
        	warning("Premature EOF",(char *)0);
		unlink(outfile); /* remove bad file */
		exit(1);
	}
	exit(0); /* no error */
}

warning(char *s, char *t) /* print warning message */
{
	fprintf(stderr, "%s: %s", progname, s);
	if (t)
		fprintf(stderr, " %s", t);
	fprintf(stderr, " line %d\n", lineno);
}