bwbasic.c

这是一个简易的basic语言解释器, 可供我们学习和改进.

bwb_fload( file )
   FILE *file;
#endif
   {

   while ( feof( file ) == FALSE )
      {
      read_line[ 0 ] = '\0';
      fgets( read_line, MAXREADLINESIZE, file );
      if ( file == stdin )
         {
         * prn_getcol( stdout ) = 1;		/* reset column */
         }
      bwb_stripcr( read_line );

      /* be sure that this is not EOF with a NULL line */

      if (( feof( file ) == FALSE ) || ( strlen( read_line ) > 0 ))
	 {
	 bwb_ladd( read_line, FALSE );
	 }
      }

   /* close file stream */

   fclose( file );

   return TRUE;
   }

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

        FUNCTION:       bwb_ladd()

        DESCRIPTION:    This function adds a new line (in the
                        buffer) to the program in memory.

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

int
#if ANSI_C
bwb_ladd( char *buffer, int replace )
#else
bwb_ladd( buffer, replace )
   char *buffer;
   int replace;
#endif
   {
   struct bwb_line *l, *previous, *p;
   static char *s_buffer;
   static int init = FALSE;
   static int prev_num = 0;
   char *newbuffer;

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_ladd(): add line <%s>",
      buffer );
   bwb_debug( bwb_ebuf );
#endif

   /* get memory for temporary buffer if necessary */

   if ( init == FALSE )
      {
      init = TRUE;

      /* Revised to CALLOC pass-thru call by JBV */
      if ( ( s_buffer = CALLOC( (size_t) MAXSTRINGSIZE + 1, sizeof( char ), "bwb_ladd" )) == NULL )
	 {
#if PROG_ERRORS
	 bwb_error( "in bwb_ladd(): failed to find memory for s_buffer" );
#else
	 bwb_error( err_getmem );
#endif
	 return FALSE;
         }
      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_ladd(): s_buffer initialized " );
   bwb_debug( bwb_ebuf );
#endif

   /* get memory for this line */

   /* Revised to CALLOC pass-thru call by JBV */
   if ( ( l = (struct bwb_line *) CALLOC( (size_t) 1, sizeof( struct bwb_line ), "bwb_ladd")) == NULL )
      {
#if PROG_ERRORS
      bwb_error( "in bwb_ladd(): failed to find memory for new line" );
#else
      bwb_error( err_getmem );
#endif
      return FALSE;
      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_ladd(): got memory." );
   bwb_debug( bwb_ebuf );
#endif

   /* note that line is not yet marked and the program must be rescanned */

   l->marked = FALSE;
   CURTASK rescan = TRUE;		/* program needs to be scanned again */
   l->xnum = FALSE;

   /* get the first element and test for a line number */

   adv_element( buffer, &( l->position ), s_buffer );

   /* set line number in line structure */

   if ( is_numconst( s_buffer ) == TRUE )
      {

      l->number = atoi( s_buffer );

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in bwb_ladd(): line is numbered, number is <%d>",
	 l->number );
      bwb_debug( bwb_ebuf );
#endif

      prev_num = l->number;
      l->xnum = TRUE;
      ++( l->position );
      newbuffer = &( buffer[ l->position ] );

      /* allocate memory and assign buffer to line buffer */

      ln_asbuf( l, newbuffer );

      }

   /* There is not a line number */

   else
      {

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in bwb_ladd(): line is not numbered, using prev <%d>",
         prev_num );
      bwb_debug( bwb_ebuf );
#endif

      newbuffer = buffer;

      /* allocate memory and assign buffer to line buffer */

      ln_asbuf( l, newbuffer );

      l->xnum = FALSE;
      l->number = prev_num;
      }

   /* find the place of the current line */

   for ( previous = &CURTASK bwb_start; previous != &CURTASK bwb_end; previous = previous->next )
      {

      /* replace a previously existing line */

      if ( ( l->xnum == (char) TRUE ) /* Better recast this one (JBV) */
         && ( previous->number == l->number )
	 && ( replace == TRUE )
	 )
         {

#if INTENSIVE_DEBUG
         sprintf( bwb_ebuf, "in bwb_ladd(): writing to previous number <%d>",
            l->number );
         bwb_debug( bwb_ebuf );
#endif

         /* allocate memory and assign buffer to line buffer */

	 ln_asbuf( previous, newbuffer );

         /* free the current line */

         /* Revised to FREE pass-thru calls by JBV */
         /* if (l->buffer != NULL) FREE( l->buffer, "bwb_ladd" ); */
         /* FREE( l, "bwb_ladd" ); */
         bwb_freeline( l ); /* JBV */

         /* and return */

         return TRUE;

         }

      /* add after previously existing line: this is to allow unnumbered
         lines that follow in sequence after a previously numbered line */

      else if (( previous->number == l->number )
	 && ( replace == FALSE )
	 )
         {
#if INTENSIVE_DEBUG
	 sprintf( bwb_ebuf, "in bwb_ladd(): adding doubled number <%d>",
	    l->number );
	 bwb_debug( bwb_ebuf);
#endif

         /* if there are multiple instances of this particular line number,
            then it is incumbent upon us to find the very last one */

         for ( p = previous; p->number == l->number; p = p->next )
            {
#if INTENSIVE_DEBUG
	    bwb_debug( "in bwb_ladd(): advancing..." );
#endif
            previous = p;
            }

         l->next = previous->next;
         previous->next = l;
         return TRUE;
         }

      /* add a new line */

      else if ( ( previous->number < l->number )
         && ( previous->next->number > l->number ))
         {
         l->next = previous->next;
         previous->next = l;

#if INTENSIVE_DEBUG
	 sprintf( bwb_ebuf, "in bwb_ladd(): added new line <%d> buffer <%s>",
	    l->number, l->buffer );
	 bwb_debug( bwb_ebuf );
#endif

         return TRUE;
         }

      }

   /* attempt to link line number has failed; free memory */

   /* Revised to FREE pass-thru calls by JBV */
   /* if (l->buffer != NULL) FREE( l->buffer, "bwb_ladd" ); */
   /* FREE( l, "bwb_ladd" ); */
   bwb_freeline( l ); /* JBV */

   sprintf( bwb_ebuf, ERR_LINENO );
   bwb_error( bwb_ebuf );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_ladd(): attempt to add line has failed" );
   bwb_debug( bwb_ebuf );
#endif

   return FALSE;

   }

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

        FUNCTION:       bwb_xtxtline()

        DESCRIPTION:    This function executes a text line, i.e.,
                        places it in memory and then relinquishes
                        control.

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

struct bwb_line *
#if ANSI_C
bwb_xtxtline( char *buffer )
#else
bwb_xtxtline( buffer )
   char *buffer;
#endif
   {
   struct bwb_line *c;
   char *p;
   int loop;

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_xtxtline(): received <%s>", buffer );
   bwb_debug( bwb_ebuf );
#endif

   /* increment xtxt stack counter */

   if ( CURTASK xtxtsc >= XTXTSTACKSIZE )
      {
      sprintf( bwb_ebuf, "Exceeded maximum xtxt stack <%d>",
         CURTASK xtxtsc );
      return &CURTASK bwb_end;
      }

   ++CURTASK xtxtsc;

   /* advance past whitespace */

   p = buffer;
   loop = TRUE;
   while( loop == TRUE )
      {

      switch( *p )
         {
         case '\0':                     /* end of string */

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "Null command line received." );
            bwb_debug( bwb_ebuf );
#endif
            --CURTASK xtxtsc;
            return &CURTASK bwb_end;
         case ' ':                      /* whitespace */
         case '\t':
            ++p;
            break;
         default:
            loop = FALSE;
            break;
         }

      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_xtxtline(): ready to get memory" );
   bwb_debug( bwb_ebuf );
#endif

/* Removed by JBV (no longer needed, done by ln_asbuf) */
/*   if ( CURTASK xtxts[ CURTASK xtxtsc ].l.buffer != NULL )
      { */
/* #if INTENSIVE_DEBUG */
/*      sprintf( bwb_ebuf, "in bwb_xtxtline(): freeing buffer memory" );
      bwb_debug( bwb_ebuf ); */
/* #endif */
        /* Revised to FREE pass-thru call by JBV */
/*      FREE( CURTASK xtxts[ CURTASK xtxtsc ].l.buffer, "bwb_xtxtline" );
      } */

   /* copy the whole line to the line structure buffer */

   ln_asbuf( &( CURTASK xtxts[ CURTASK xtxtsc ].l ), buffer );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_xtxtline(): copied to line buffer <%s>.",
      CURTASK xtxts[ CURTASK xtxtsc ].l.buffer );
   bwb_debug( bwb_ebuf );
#endif

   /* set line number in line structure */

   CURTASK xtxts[ CURTASK xtxtsc ].l.number = 0;
   CURTASK xtxts[ CURTASK xtxtsc ].l.marked = FALSE;

   /* execute the line as BASIC command line */

   CURTASK xtxts[ CURTASK xtxtsc ].l.next = &CURTASK bwb_end;
   c = &( CURTASK xtxts[ CURTASK xtxtsc ].l );
   c->position = 0;

#if THEOLDWAY
   do
      {
      c = bwb_xline( c );
      }

   while( c != &CURTASK bwb_end );
#endif

   bwb_incexec();		/* increment EXEC stack */
   bwb_setexec( c, 0, EXEC_NORM );		/* and set current line in it */

   /* decrement xtxt stack counter ??? */

   --CURTASK xtxtsc;

   return c;

   }

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

        FUNCTION:       bwb_incexec()

        DESCRIPTION:    This function increments the EXEC
			stack counter.

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

#if ANSI_C
extern void
bwb_incexec( void )
   {
#else
void
bwb_incexec()
   {
#endif
   ++CURTASK exsc;

   if ( CURTASK exsc >= EXECLEVELS )
      {
      --CURTASK exsc;
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in bwb_incexec(): incremented EXEC stack past max <%d>",
         EXECLEVELS );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_overflow );
#endif
      }

   CURTASK excs[ CURTASK exsc ].while_line = NULL;
   CURTASK excs[ CURTASK exsc ].wend_line  = NULL;
   CURTASK excs[ CURTASK exsc ].n_cvs = 0;
   CURTASK excs[ CURTASK exsc ].local_variable = NULL;

   }

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

        FUNCTION:       bwb_decexec()

        DESCRIPTION:    This function decrements the EXEC
			stack counter.

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

#if ANSI_C
extern void
bwb_decexec( void )
   {
#else
void
bwb_decexec()
   {
#endif

   /* decrement the exec stack counter */

   --CURTASK exsc;

   if ( CURTASK exsc < -1 )
      {
      CURTASK exsc = -1;
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in bwb_decexec(): decremented EXEC stack past min <-1>" );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_overflow );
#endif
      }

   /* check for EXEC_ON and decrement recursively */

   if ( CURTASK excs[ CURTASK exsc ].code == EXEC_ON )
      {

      /* Revised to FREE pass-thru calls by JBV */
      /* FREE( CURTASK excs[ CURTASK exsc ].while_line->buffer, "bwb_decexec" ); */
      /* FREE( CURTASK excs[ CURTASK exsc ].while_line, "bwb_decexec" ); */
      bwb_freeline( CURTASK excs[ CURTASK exsc ].while_line ); /* JBV */

      bwb_decexec();
      }

   }

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

        FUNCTION:       bwb_setexec()

        DESCRIPTION:    This function sets the line and position
			for the next call to bwb_execline();

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

#if ANSI_C
extern int
bwb_setexec( struct bwb_line *l, int position, int code )
   {
#else
int
bwb_setexec( l, position, code )
   struct bwb_line *l;
   int position;
   int code;
   {
#endif

   CURTASK excs[ CURTASK exsc ].line = l;
   CURTASK excs[ CURTASK exsc ].position = position;
   CURTASK excs[ CURTASK exsc ].code = code;

   return TRUE;

   }

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

        FUNCTION:       bwb_mainloop()

        DESCRIPTION:    This C function performs one iteration
                        of the interpreter. In a non-preemptive
                        scheduler, this function should be called
                        by the scheduler, not by bwBASIC code.

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

void
#if ANSI_C
bwb_mainloop( void )