%{#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);}