bwbasic.c

这是一个简易的basic语言解释器, 可供我们学习和改进.

#else
bwb_mainloop()
#endif
   {
   if ( CURTASK exsc > -1 )
      {
      bwb_execline();			/* execute one line of program */
      }
#if INTERACTIVE
   else
      {
      bwb_interact();			/* get user interaction */
      }
#endif
   }

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

        FUNCTION:       bwb_execline()

        DESCRIPTION:    This function executes a single line of
                        a program in memory. This function is
			called by bwb_mainloop().

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

void
#if ANSI_C
bwb_execline( void )
#else
bwb_execline()
#endif
   {
   struct bwb_line *r, *l;

   l = CURTASK excs[ CURTASK exsc ].line;

   /* if the line is &CURTASK bwb_end, then break out of EXEC loops */

   if ( l == &CURTASK bwb_end )
      {
      CURTASK exsc = -1;
      return;
      }

   /* Check for wacko line numbers  */

#if INTENSIVE_DEBUG
   if ( l->number < -1 )
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in bwb_execline(): received line number <%d> < -1",
         l->number );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_syntax );
#endif
      return;
      }

   if ( l->number > MAXLINENO )
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in bwb_execline(): received line number <%d> > MAX <%d>",
         l->number, MAXLINENO );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_syntax );
#endif
      return;
      }
#endif

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_execline(): buffer <%s>",
      &( l->buffer[ l->position ] ) );
   bwb_debug( bwb_ebuf );
#endif

   /* Print line number if trace is on */

   if ( bwb_trace == TRUE )
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "[ %d ]", l->number );
      prn_xprintf( errfdevice, bwb_ebuf );
#else
      if ( l->number > 0 )
         {
         sprintf( bwb_ebuf, "[ %d ]", l->number );
	 prn_xprintf( errfdevice, bwb_ebuf );
         }
#endif
      }

   /* Set current line for error/break handling */

   CURTASK number = l->number;
   CURTASK bwb_l = l;

   /* advance beyond whitespace */

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

   /*  advance past segment delimiter and warn */

#if MULTISEG_LINES
   if ( l->buffer[ l->position ] == ':' )
      {
      ++( l->position );
      adv_ws( l->buffer, &( l->position ) );
      }
   l->marked = FALSE;
#else
#if PROG_ERRORS
   if ( l->buffer[ l->position ] == ':' )
      {
      ++( l->position );
      adv_ws( l->buffer, &( l->position ) );
      sprintf( bwb_ebuf, "Enable MULTISEG_LINES for multi-segmented lines",
         VERSION );
      bwb_error( bwb_ebuf );
      }
#endif
#endif

   /* set positions in buffer */

#if MULTISEG_LINES
   if ( ( l->marked != TRUE ) || ( l->position > l->startpos ))
      {
      line_start( l->buffer, &( l->position ), &( l->lnpos ), &( l->lnum ),
         &( l->cmdpos ), &( l->cmdnum ), &( l->startpos ) );
      l->marked = TRUE;
      }
   else
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in bwb_execline(): line <%d> is already marked",
          l->number );
      bwb_debug( bwb_ebuf );
#endif
      }
   l->position = l->startpos;
#else				/* not MULTISEG_LINES */
   line_start( l->buffer, &( l->position ), &( l->lnpos ), &( l->lnum ),
      &( l->cmdpos ), &( l->cmdnum ), &( l->startpos ) );
   if ( l->position < l->startpos )
      {
      l->position = l->startpos;
      }
#endif

   /* if there is a BASIC command in the line, execute it here */

   if ( l->cmdnum > -1 )
      {

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in bwb_execline(): executing <%s>", l->buffer );
      bwb_debug( bwb_ebuf );
#endif

      /* execute the command vector */

      r = bwb_cmdtable[ l->cmdnum ].vector ( l );

      }

   /* No BASIC command; try to execute it as a shell command */

#if COMMAND_SHELL
   else
      {

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "Breaking out to shell, line num <%d> buf <%s> cmd <%d> pos <%d>",
         l->number, &( l->buffer[ l->position ] ), l->cmdnum, l->position );
      bwb_debug( bwb_ebuf );
      getchar();
#endif

      bwx_shell( l );
      bwb_setexec( l->next, 0, CURTASK excs[ CURTASK exsc ].code );
      return;
      }

#else				/* COMMAND_SHELL == FALSE */

   else
     {
     bwb_error( err_uc );
     }

#endif

   /* check for end of line: if so, advance to next line and return */

   adv_ws( r->buffer, &( r->position ) );
   switch( r->buffer[ r->position ] )
      {
      case '\n':
      case '\r':
      case '\0':

#if INTENSIVE_DEBUG
	 sprintf( bwb_ebuf, "in bwb_execline(): detected end of line" );
	 bwb_debug( bwb_ebuf );
#endif

	 r->next->position = 0;
         bwb_setexec( r->next, 0, CURTASK excs[ CURTASK exsc ].code );
         return;			/* and return */
      }

   /* else reset with the value in r */

   bwb_setexec( r, r->position, CURTASK excs[ CURTASK exsc ].code );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_execline(): exit setting line number <%d>",
      r->number );
   bwb_debug( bwb_ebuf );
#endif

   }

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

        FUNCTION:       ln_asbuf()

        DESCRIPTION:    This function allocates memory and copies
			a null-terminated string to a line buffer.

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

int
#if ANSI_C
ln_asbuf( struct bwb_line *l, char *s )
#else
ln_asbuf( l, s )
   struct bwb_line *l;
   char *s;
#endif
   {

/* Reinstated by JBV */
/* #if DONTDOTHIS */		/* but why not? */
   if ( l->buffer != NULL )
      {
      /* Revised to FREE pass-thru call by JBV */
      FREE( l->buffer, "ln_asbuf" );
      l->buffer = NULL; /* JBV */
      }
/* #endif */

   /* Revised to CALLOC pass-thru call by JBV */
   if ( ( l->buffer = CALLOC( strlen( s ) + 2, sizeof( char ), "ln_asbuf") )
      == NULL )
      {
#if PROG_ERRORS
      bwb_error( "in ln_asbuf(): failed to find memory for new line" );
#else
      bwb_error( err_getmem );
#endif
      return FALSE;
      }

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

   strcpy( l->buffer, s );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in ln_asbuf(): allocated buffer <%s>", l->buffer );
   bwb_debug( bwb_ebuf );
#endif

   /* strip CR from the buffer */

   bwb_stripcr( l->buffer );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in ln_asbuf(): stripped CRs" );
   bwb_debug( bwb_ebuf );
#endif

   return TRUE;

   }

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

        FUNCTION:       bwb_gets()

        DESCRIPTION:    This function reads a single line from
                        the specified buffer.

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

int
#if ANSI_C
bwb_gets( char *buffer )
#else
bwb_gets( buffer )
   char *buffer;
#endif
   {
   struct bwb_variable *v;
   char tbuf[ MAXSTRINGSIZE + 1 ];
#if PARACT
   char ubuf[ MAXSTRINGSIZE + 1 ];
#endif

   CURTASK number = 0;

   v = var_find( DEFVNAME_PROMPT );
   str_btoc( tbuf, var_getsval( v ) );
#if PARACT
   sprintf( ubuf, "TASK %d %s", bwb_curtask, tbuf );
   strcpy( tbuf, ubuf );
#endif

   bwx_input( tbuf, buffer );

   return TRUE;
   }

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

        FUNCTION:       break_mes()

        DESCRIPTION:    This function is called (a) by a SIGINT
			signal or (b) by error-handling routines.
			It prints an error message then calls
			break_handler() to handle the program
			interruption.

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

void
#if ANSI_C
break_mes( int x )
#else
break_mes( x )
   int x;
#endif
   {
   static char *tmp_buffer;
   static int init = FALSE;

   /* get memory for temporary buffer if necessary */

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

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

   CURTASK expsc = 0;

   sprintf( tmp_buffer, "\r%s %d\n", MES_BREAK, CURTASK number );
   prn_xprintf( errfdevice, tmp_buffer );

   break_handler();

   }

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

	FUNCTION:       break_handler()

	DESCRIPTION:    This function is called by break_mes()
			and handles program interruption by break
			(or by the STOP command).

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

void
#if ANSI_C
break_handler( void )
#else
break_handler()
#endif
   {

#if INTERACTIVE		/* INTERACTIVE: reset counters and jump back to mark */

   /* reset all stack counters */

   CURTASK exsc = -1;
   CURTASK expsc = 0;
   CURTASK xtxtsc = 0;
   err_gosubl[ 0 ] = '\0';

   /* reset the break handler */

#if HAVE_SIGNAL
   signal( SIGINT, break_mes );
#endif

#if HAVE_LONGJUMP
   longjmp( mark, -1 );
#else		/* HAVE_LONGJUMP = FALSE; no jump available; terminate */   
   bwx_terminate();
#endif   

#else		/* nonINTERACTIVE:  terminate immediately */

   bwx_terminate();

#endif

   }


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

	FUNCTION:       is_ln()

	DESCRIPTION:    This function determines whether a program
			line (in buffer) begins with a line number.

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

int
#if ANSI_C
is_ln( char *buffer )
#else
is_ln( buffer )
   char *buffer;
#endif
   {
   static int position;

   position = 0;
   adv_ws( buffer, &position );
   switch( buffer[ position ] )
      {
      case '0':
      case '1':
      case '2':
      case '3':
      case '4':
      case '5':
      case '6':
      case '7':
      case '8':
      case '9':
         return TRUE;
      default:
         return FALSE;
      }
   }


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

	FUNCTION:       CALLOC()

	DESCRIPTION:    Pass-thru function to calloc() for debugging
			purposes.  Added by JBV 10/95

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

void *
#if ANSI_C
CALLOC( size_t nelem, size_t elsize, char *str )
#else
CALLOC( nelem, elsize, str )
   size_t nelem;
   size_t elsize;
   char *str;
#endif
{
    void *ptr;

    ptr = calloc(nelem, elsize);
    /* printf("%x %x\n", ptr, mallocblksize(ptr)); */
    return ptr;
}

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

	FUNCTION:       FREE()

	DESCRIPTION:    Pass-thru function to free() for debugging
			purposes.  Added by JBV 10/95

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

void
#if ANSI_C
FREE( void *ptr, char *str )
#else
FREE( ptr, str )
   void *ptr;
   char *str;
#endif
{
    /* printf("%x\n", ptr); */
    free(ptr);
}