bwb_cnd.c

这是一个简易的basic语言解释器, 可供我们学习和改进.

            bwb_debug( bwb_ebuf );
#endif

            if ( c_level == 0 )
               {
               return current;
               }
            }
         }
      }

#if PROG_ERRORS
   sprintf( bwb_ebuf, "SELECT without CASE" );
   bwb_error( bwb_ebuf );
#else
   bwb_error( err_syntax  );
#endif

   return NULL;

   }

/***************************************************************

        FUNCTION:       find_case()

        DESCRIPTION:    This function searches for a line containing
                        an END SELECT statement corresponding to a previous
                        SELECT CASE statement.

***************************************************************/

#if ANSI_C
static struct bwb_line *
find_endselect( struct bwb_line *l )
#else
static struct bwb_line *
find_endselect( l )
   struct bwb_line *l;
#endif
   {
   struct bwb_line *current;
   register int c_level;
   int position;

   c_level = 1;
   for ( current = l->next; current != &CURTASK bwb_end; current = current->next )
      {
      position = 0;
      if ( current->marked != TRUE )
         {
         line_start( current->buffer, &position, &( current->lnpos ),
            &( current->lnum ),
            &( current->cmdpos ),
            &( current->cmdnum ),
            &( current->startpos ) );
         }
      current->position = current->startpos;

      if ( current->cmdnum > -1 )
         {

         if ( bwb_cmdtable[ current->cmdnum ].vector == bwb_select )
            {
            ++c_level;

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in find_case(): found SELECT at line %d, level %d",
               current->number, c_level );
            bwb_debug( bwb_ebuf );
#endif

            }
         else if ( is_endselect( current ) == TRUE )
            {
            --c_level;

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in find_endif(): found END SELECT at line %d, level %d",
               current->number, c_level );
            bwb_debug( bwb_ebuf );
#endif

            if ( c_level == 0 )
               {
               return current;
               }
            }
         }
      }

#if PROG_ERRORS
   sprintf( bwb_ebuf, "SELECT without END SELECT" );
   bwb_error( bwb_ebuf );
#else
   bwb_error( err_syntax  );
#endif

   return NULL;

   }

/***************************************************************

	FUNCTION:       is_endselect()

	DESCRIPTION:    This C function attempts to determine if
			a given line contains an END SELECT statement.

***************************************************************/

#if ANSI_C
static int
is_endselect( struct bwb_line *l )
#else
static int
is_endselect( l )
   struct bwb_line *l;
#endif
   {
   int position;
   char tbuf[ MAXVARNAMESIZE + 1];

   if ( bwb_cmdtable[ l->cmdnum ].vector != bwb_xend )
      {
      return FALSE;
      }

   position = l->startpos;
   adv_ws( l->buffer, &position );
   adv_element( l->buffer, &position, tbuf );
   bwb_strtoupper( tbuf );

   if ( strcmp( tbuf, "SELECT" ) == 0 )
      {
      return TRUE;
      }

   return FALSE;

   }

/***************************************************************

        FUNCTION:       bwb_endselect()

        DESCRIPTION:    This function handles the BASIC END
                        SELECT statement.

	SYNTAX:		END SELECT

***************************************************************/

#if ANSI_C
struct bwb_line *
bwb_endselect( struct bwb_line *l )
#else
struct bwb_line *
bwb_endselect( l )
   struct bwb_line *l;
#endif
   {

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_endselect(): entered function" );
   bwb_debug( bwb_ebuf );
#endif

   if (  ( CURTASK excs[ CURTASK exsc ].code != EXEC_SELTRUE  )
      && ( CURTASK excs[ CURTASK exsc ].code != EXEC_SELFALSE ))
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in bwb_endselect(): END SELECT without SELECT" );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_syntax );
#endif
      }

   bwb_decexec();


#if MULTISEG_LINES
   adv_eos( l->buffer, &( l->position ));
#endif
   return bwb_zline( l );
   }

#endif				/* STRUCT_CMDS */

#if COMMON_CMDS || STRUCT_CMDS

/***    WHILE-WEND ***/

/***************************************************************

        FUNCTION:       bwb_while()

        DESCRIPTION:    This function handles the BASIC WHILE
			statement and also the ANSI DO WHILE
			statement.

	SYNTAX:		WHILE expression
			DO WHILE expression

***************************************************************/

#if ANSI_C
struct bwb_line *
bwb_while( struct bwb_line *l )
#else
struct bwb_line *
bwb_while( l )
   struct bwb_line *l;
#endif
   {
   struct exp_ese *e;
   struct bwb_line *r;

   /* call bwb_exp() to interpret the expression */

   e = bwb_exp( l->buffer, FALSE, &( l->position ) );

   if ( (int) exp_getnval( e ) == TRUE )
      {

      /* if this is the first time at this WHILE statement, note it */

      if ( CURTASK excs[ CURTASK exsc ].while_line != l )
         {

         bwb_incexec();
         CURTASK excs[ CURTASK exsc ].while_line = l;

         /* find the WEND statement (or LOOP statement) */

#if STRUCT_CMDS
	 if ( l->cmdnum == getcmdnum( CMD_DO ))
            {
	    CURTASK excs[ CURTASK exsc ].wend_line = find_loop( l );
            }
         else
            {
	    CURTASK excs[ CURTASK exsc ].wend_line = find_wend( l );
	    }
#else
	 CURTASK excs[ CURTASK exsc ].wend_line = find_wend( l );
#endif

         if ( CURTASK excs[ CURTASK exsc ].wend_line == NULL )
            {
            return bwb_zline( l );
            }

#if INTENSIVE_DEBUG
         sprintf( bwb_ebuf, "in bwb_while(): initialize WHILE loop, line <%d>",
            l->number );
         bwb_debug( bwb_ebuf );
#endif

         }
#if INTENSIVE_DEBUG
      else
         {
         sprintf( bwb_ebuf, "in bwb_while(): return to WHILE loop, line <%d>",
            l->number );
         bwb_debug( bwb_ebuf );
         }
#endif

      bwb_setexec( l, l->position, EXEC_WHILE );
      return bwb_zline( l );
      }
   else
      {
      CURTASK excs[ CURTASK exsc ].while_line = NULL;
      r = CURTASK excs[ CURTASK exsc ].wend_line;
      bwb_setexec( r, 0, CURTASK excs[ CURTASK exsc - 1 ].code );
      r->position = 0;
      bwb_decexec();
      return r;
      }

   }

/***************************************************************

        FUNCTION:       bwb_wend()

        DESCRIPTION:    This function handles the BASIC WEND
			statement and the LOOP statement ending
			a DO WHILE loop.

	SYNTAX:		WEND
			LOOP

***************************************************************/

#if ANSI_C
struct bwb_line *
bwb_wend( struct bwb_line *l )
#else
struct bwb_line *
bwb_wend( l )
   struct bwb_line *l;
#endif
   {

   /* check integrity of WHILE loop */

   if ( CURTASK excs[ CURTASK exsc ].code != EXEC_WHILE )
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in bwb_wend(): exec stack code != EXEC_WHILE" );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_syntax );
#endif
      }

   if ( CURTASK excs[ CURTASK exsc ].while_line == NULL )
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in bwb_wend(): exec stack while_line == NULL" );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_syntax );
#endif
      }

   /* reset to the top of the current WHILE loop */

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_wend() return to line <%d>",
      CURTASK excs[ CURTASK exsc ].while_line->number );
   bwb_debug( bwb_ebuf );
#endif

   CURTASK excs[ CURTASK exsc ].while_line->position = 0;
   bwb_setexec( CURTASK excs[ CURTASK exsc ].while_line, 0, EXEC_WHILE );

   return CURTASK excs[ CURTASK exsc ].while_line;

   }

/***************************************************************

        FUNCTION:       find_wend()

        DESCRIPTION:    This function searches for a line containing
                        a WEND statement corresponding to a previous
                        WHILE statement.

***************************************************************/

#if ANSI_C
static struct bwb_line *
find_wend( struct bwb_line *l )
#else
static struct bwb_line *
find_wend( l )
   struct bwb_line *l;
#endif
   {
   struct bwb_line *current;
   register int w_level;
   int position;

   w_level = 1;
   for ( current = l->next; current != &CURTASK bwb_end; current = current->next )
      {
      position = 0;
      if ( current->marked != TRUE )
         {
         line_start( current->buffer, &position, &( current->lnpos ),
            &( current->lnum ),
            &( current->cmdpos ),
            &( current->cmdnum ),
            &( current->startpos ) );
         }
      current->position = current->startpos;

      if ( current->cmdnum > -1 )
         {

         if ( bwb_cmdtable[ current->cmdnum ].vector == bwb_while )
            {
            ++w_level;

#if INTENSIVE_DEBUG
	    sprintf( bwb_ebuf, "in find_wend(): found WHILE at line %d, level %d",
               current->number, w_level );
            bwb_debug( bwb_ebuf );
#endif

            }
         else if ( bwb_cmdtable[ current->cmdnum ].vector == bwb_wend )
            {
            --w_level;

#if INTENSIVE_DEBUG
	    sprintf( bwb_ebuf, "in find_wend(): found WEND at line %d, level %d",
               current->number, w_level );
            bwb_debug( bwb_ebuf );
#endif

            if ( w_level == 0 )
               {
               return current->next;
               }
            }
         }
      }

#if PROG_ERRORS
   sprintf( bwb_ebuf, "in find_wend(): WHILE without WEND" );
   bwb_error( bwb_ebuf );
#else
   bwb_error( err_syntax  );
#endif

   return NULL;

   }

#if STRUCT_CMDS

/***************************************************************

	FUNCTION:       find_loop()

	DESCRIPTION:    This function searches for a line containing
			a LOOP statement corresponding to a previous
			DO statement.

***************************************************************/

#if ANSI_C
extern struct bwb_line *
find_loop( struct bwb_line *l )
#else
extern struct bwb_line *
find_loop( l )
   struct bwb_line *l;
#endif
   {
   struct bwb_line *current;
   register int w_level;
   int position;

   w_level = 1;
   for ( current = l->next; current != &CURTASK bwb_end; current = current->next )
      {
      position = 0;
      if ( current->marked != TRUE )
	 {
	 line_start( current->buffer, &position, &( current->lnpos ),
	    &( current->lnum ),
	    &( current->cmdpos ),
	    &( current->cmdnum ),
	    &( current->startpos ) );
	 }
      current->position = current->startpos;

      if ( current->cmdnum > -1 )
	 {

	 if ( bwb_cmdtable[ current->cmdnum ].vector == bwb_do )
	    {
	    ++w_level;

#if INTENSIVE_DEBUG
	    sprintf( bwb_ebuf, "in find_loop(): found DO at line %d, level %d",
	       current->number, w_level );
	    bwb_debug( bwb_ebuf );
#endif

	    }
	 else if ( bwb_cmdtable[ current->cmdnum ].vector == bwb_loop )
	    {
	    --w_level;

#if INTENSIVE_DEBUG
	    sprintf( bwb_ebuf, "in fnd_loop(): found LOOP at line %d, level %d",
	       current->number, w_level );
	    bwb_debug( bwb_ebuf );
#endif

	    if ( w_level == 0 )
	       {
	       return current->next;
	       }
	    }
	 }
      }

#if PROG_ERRORS
   sprintf( bwb_ebuf, "in find_loop(): DO without LOOP" );
   bwb_error( bwb_ebuf );
#else
   bwb_error( err_syntax  );
#endif

   return NULL;

   }

#endif                          /* STRUCT_CMDS */

#endif                          /* COMMON_CMDS || STRUCT_CMDS */

/***    FOR-NEXT ***/

/***************************************************************

        FUNCTION:       bwb_for()

        DESCRIPTION:    This function handles the BASIC FOR
                        statement.

	SYNTAX:		FOR counter = start TO finish [STEP increment]

***************************************************************/

#if ANSI_C
struct bwb_line *
bwb_for( struct bwb_line *l )
#else
struct bwb_line *
bwb_for( l )
   struct bwb_line *l;
#endif
   {
   register int n;
   int e, loop;
   int to, step, p;
   int for_step, for_target;
   struct exp_ese *exp;
   struct bwb_variable *v;
   char tbuf[ MAXSTRINGSIZE + 1 ];

   /* get the variable name */

   exp_getvfname( &( l->buffer[ l->position ] ), tbuf );
   l->position += strlen( tbuf );
   v = var_find( tbuf );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_for(): variable name <%s>.", v->name );
   bwb_debug( bwb_ebuf );
#endif

   /*--------------------------------------------------------------*/
   /* Make sure we are in the right FOR-NEXT level!                */
   /* If we aren't (which could happen for legit reasons), fix the */
   /* exec stack.                                                  */
   /* JBV, 9/20/95                                                 */
   /*--------------------------------------------------------------*/
   if (v == CURTASK excs[ CURTASK exsc].local_variable) bwb_decexec();

   /* at this point one should find an equals sign ('=') */

   adv_ws( l->buffer, &( l->position ) );

   if ( l->buffer[ l->position ] != '=' )
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in bwb_for(): failed to find equals sign, buf <%s>",
         &( l->buffer[ l->position ] ) );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_syntax );
#endif
      return bwb_zline( l );
      }
   else
      {
      ++( l->position );
      }

   /* Find the TO and STEP statements */

   cnd_tostep( l->buffer, l->position, &to, &step );

   /* if there is no TO statement, then an error has ocurred */

   if ( to < 1 )
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "FOR statement without TO" );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_syntax  );
#endif
      return bwb_zline( l );
      }

   /* copy initial value to buffer and evaluate it */

   tbuf[ 0 ] = '\0';
   p = 0;
   for ( n = l->position; n < to; ++n )
      {
      tbuf[ p ] = l->buffer[ n ];
      ++p;
      ++l->position;
      tbuf[ p ] = '\0';
      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_for(): initial value string <%s>",
      tbuf );
   bwb_debug( bwb_ebuf );
#endif

   p = 0;
   exp = bwb_exp( tbuf, FALSE, &p );