expr.lma

一个c语言写做的编译器的源码

/*@A (C) 1992 Allen I. Holub                                                */
   /* This is the llama input file for the expression compiler.
   */

%term  PLUS 		/*  +					*/
       TIMES		/*  *					*/
%term  NUM_OR_ID	/*  a number or identifier		*/
%term  LP		/*  (					*/
%term  RP		/*  )					*/
%term  SEMI		/*  ;					*/

%{
#include <tools/debug.h>

/*------------------------------------------------------------
 * Rvalue names are stored on a stack. name() pops a name off the stack and
 * freename(x) puts it back. A real compiler would do some checking for
 * stack overflow here but there's no point in cluttering the code for now.
 */

char *Namepool[] =
{
    "t0", "t1", "t2", "t3", "t4", "t5", "t6", "t7", "t8", "t9"
};
char **Namep = Namepool ;

char *newname P((void))     	     { return(*Namep++);     }
UNIX( char *freename (x) char *x;  )
ANSI( char *freename (   char *x ) ) { return(*--Namep = x); }

extern char *yytext;
extern int  yyleng;

#define YYSTYPE char*
%}

%synch SEMI RP

%%
/* A small expression grammar that recognizes numbers, names, addition (+),
 * multiplication (*), and parentheses. Expressions associate left to right
 * unless parentheses force it to go otherwise. * is higher precedence than +
 */

stmt	:	/* eps */
	|	{$1=$2=newname();} expr {freename($0);} SEMI stmt
	;

expr	:	term expr'
	;

expr'	: 	PLUS {$1=$2=newname();} term
			{ yycode("%s+=%s\n", $$, $0); freename($0); } expr'
	|	/* epsilon */
	;

term	:	factor term'
	;

term'	:	TIMES {$1=$2=newname();} factor
			{ yycode("%s*=%s\n", $$, $0); freename($0);} term'
	|	/* epsilon */
	;

factor	:	NUM_OR_ID { yycode("%s=%0.*s\n", $$, yyleng, yytext); }
	|	LP expr RP
	;
%%
/*------------------------------------------------------------*/

void yy_init_llama( p )
void *p;
{
    ((yyvstype *)p)->left = ((yyvstype *)p)->right = "-" ;
}

#ifdef __TURBOC__
#pragma argsused
#endif

char *yypstk(tovs, tods)
void *tovs;
char *tods;
{
    static char buf[128];
    sprintf(buf,"[%s,%s]", ((yyvstype *)tovs)->left, ((yyvstype *)tovs)->right);
    return buf;
}

void main( argc, argv )
char	**argv;
{
    yy_get_args( argc, argv );
    yyparse();
    exit( 0 );
}