bwb_stc.c

这是一个简易的basic语言解释器, 可供我们学习和改进.

      {
      if ( CURTASK excs[ level ].code == EXEC_DO )
	 {
	 next_line = CURTASK excs[ CURTASK level ].wend_line;
	 found = TRUE;
	 }
      else
	 {
	 --level;
	 }
      }
   while ( ( level >= 0 ) && ( found == FALSE ) );

   if ( found != TRUE )
      {

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

      return bwb_zline( l );

      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in bwb_exitdo(): level found is <%d>, current <%d>",
      level, CURTASK exsc );
   bwb_debug( bwb_ebuf );
#endif

   /* decrement below the level of the NEXT statement */

   while( CURTASK exsc >= level )
      {
      bwb_decexec();
      }

   /* set the next line in the exec stack */

   next_line->position = 0;
   bwb_setexec( next_line, 0, EXEC_NORM );

   return next_line;

   }

#endif					/* STRUCT_CMDS */

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

	FUNCTION:       bwb_vtov()

	DESCRIPTION:    This function assigns the value of one
			bwBASIC variable (src) to the value of another
			bwBASIC variable (dst).

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

#if ANSI_C
struct bwb_variable *
bwb_vtov( struct bwb_variable *dst,
   struct bwb_variable *src )
#else
struct bwb_variable *
bwb_vtov( dst, src )
   struct bwb_variable *dst;
   struct bwb_variable *src;
#endif
   {

   if ( dst == src )
      {
      return dst;
      }

   if ( src->type != dst->type )
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in bwb_vtov(): mismatch src <%s> type <%d> dst <%s> type <%d>",
	 src->name, src->type, dst->name, dst->type );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_mismatch );
#endif
      return NULL;
      }

   if ( dst->type == NUMBER )
      {

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in bwb_vtov(): assigning var <%s> val <%lf> to var <%s>",
	 src->name, var_getnval( src ), dst->name );
      bwb_debug( bwb_ebuf );
#endif

      * var_findnval( dst, dst->array_pos ) = var_getnval( src );
      }
   else
      {
      str_btob( var_getsval( dst ), var_getsval( src ) );
      }

   return dst;
   }

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

	FUNCTION:       bwb_etov()

	DESCRIPTION:    This function assigns the value of a
			bwBASIC expression stack element (src)
			to the value of a bwBASIC variable (dst).

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

#if ANSI_C
struct bwb_variable *
bwb_etov( struct bwb_variable *dst, struct exp_ese *src )
#else
struct bwb_variable *
bwb_etov( dst, src )
   struct bwb_variable *dst;
   struct exp_ese *src;
#endif
   {

   if ( (int) src->type != dst->type )
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in bwb_etov(): mismatch src <%d> dst <%d>",
         src->type, dst->type );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_mismatch );
#endif
      return NULL;
      }

   if ( dst->type == NUMBER )
      {
      * var_findnval( dst, dst->array_pos ) = exp_getnval( src );
      }
   else
      {
      str_btob( var_getsval( dst ), exp_getsval( src ) );
      }

   return dst;
   }

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

	FUNCTION:       var_pos()

	DESCRIPTION:    This function returns the name of a
			local variable at a specified position
			in the local variable list.

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

#if ANSI_C
struct bwb_variable *
var_pos( struct bwb_variable *firstvar, int p )
#else
struct bwb_variable *
var_pos( firstvar, p )
   struct bwb_variable *firstvar;
   int p;
#endif
   {
   register int c;
   struct bwb_variable *v;

   v = firstvar;
   for ( c = 0; c != p; ++c )
      {
      v = v->next;
      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in var_pos(): returning pos <%d> variable <%s>",
      p, v->name );
   bwb_debug( bwb_ebuf );
#endif

   return v;
   }

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

	FUNCTION:       fslt_addcallvar()

	DESCRIPTION:    This function adds a calling variable
			to the FUNCTION-SUB lookup table at
			a specific level.

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

#if ANSI_C
int
fslt_addcallvar( struct bwb_variable *v )
#else
int
fslt_addcallvar( v )
   struct bwb_variable *v;
#endif
   {

   if ( CURTASK excs[ CURTASK exsc ].n_cvs >= MAX_FARGS )
      {
#if PROG_ERRORS
      sprintf( bwb_ebuf, "in fslt_addcallvar(): Maximum number of Function Args Exceeded" );
      bwb_error( bwb_ebuf );
#else
      bwb_error( err_overflow );
#endif
      }

   CURTASK excs[ CURTASK exsc ].calling_variable[ CURTASK excs[ CURTASK exsc ].n_cvs ] = v;
   ++CURTASK excs[ CURTASK exsc ].n_cvs;

   return TRUE;

   }

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

	FUNCTION:       exp_ufnc()

        DESCRIPTION:	This C function interprets a user-defined
			function, returning its value at the current
			level of the expression stack.

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

#if ANSI_C
int
exp_ufnc( char *expression )
#else
int
exp_ufnc( expression )
   char *expression;
#endif
   {
   char tbuf[ MAXSTRINGSIZE + 1 ];
   struct bwb_line *call_line;
   struct fslte *f, *c;
   struct bwb_variable *v, *r;
   struct exp_ese *e;
   int save_elevel;
   int position, epos;
#if INTENSIVE_DEBUG
   register int i;
#endif

   position = 0;

   /* get the function name in tbuf */

   exp_getvfname( expression, tbuf );

   /* find the function name in the function-subroutine lookup table */

   for ( f = CURTASK fslt_start.next; f != &CURTASK fslt_end; f = f->next )
      {
      if ( strcmp( f->name, tbuf ) == 0 )
	 {
#if INTENSIVE_DEBUG
	 sprintf( bwb_ebuf, "in exp_ufnc(): found user function <%s>",
	    tbuf );
	 bwb_debug( bwb_ebuf );
#endif
	 c = f; 		/* current function-subroutine lookup table element */
	 call_line = f->line;	/* line to call for function */
	 }
      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_ufnc(): call to function <%s>", tbuf );
   bwb_debug( bwb_ebuf );
#endif

   position += strlen( tbuf );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_ufnc(): found line <%s>",
      call_line->buffer );
   bwb_debug( bwb_ebuf );
#endif

   /* save the old position on the EXEC stack */

   bwb_setexec( CURTASK excs[ CURTASK exsc ].line,
      position, CURTASK excs[ CURTASK exsc ].code );
   save_elevel = CURTASK exsc;

   /* increment and set new EXEC stack */

   bwb_incexec();
   call_line->position = 0;
   bwb_setexec( call_line, 0, EXEC_FUNCTION );

   /* attach local variables */

   CURTASK excs[ CURTASK exsc ].local_variable = c->local_variable;

#if INTENSIVE_DEBUG
   i = 0;
   sprintf( bwb_ebuf, "in exp_ufnc(): <%s> attached local variables EXEC level <%d>",
      tbuf, CURTASK exsc );
   bwb_debug( bwb_ebuf );
   for ( v = CURTASK excs[ CURTASK exsc ].local_variable; v != NULL; v = v->next )
      {
      sprintf( bwb_ebuf, "in exp_ufnc():   <%s> level <%d> variable <%d> name <%s>",
	 tbuf, CURTASK exsc, i, v->name );
      bwb_debug( bwb_ebuf );
      ++i;
      }
   getchar();
#endif

   /* read calling variables for this call */

   call_readargs( c, expression, &position );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_ufnc(): current buffer <%s>",
      &( call_line->buffer[ c->startpos ] ) );
   bwb_debug( bwb_ebuf );
#endif

   /* determine if single-line function */

   epos = c->startpos;
   adv_ws( call_line->buffer, &epos );
   if ( call_line->buffer[ epos ] == '=' )
      {

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_ufnc(): found SINGLE-LINE function" );
      bwb_debug( bwb_ebuf );
#endif

      ++epos;
      call_line->position = epos;
      bwb_setexec( call_line, epos, EXEC_FUNCTION );

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_ufnc(): single line: parse <%s>",
	 &( call_line->buffer[ epos ] ) );
      bwb_debug( bwb_ebuf );
#endif

      e = bwb_exp( call_line->buffer, FALSE, &epos );
      v = var_find( tbuf );

#if INTENSIVE_DEBUG
      if ( e->type == STRING )
	 {
	 sprintf( bwb_ebuf, "in exp_ufnc(): expression returns <%d>-byte string",
	    exp_getsval( e )->length );
	 bwb_debug( bwb_ebuf );
	 }
      else
	 {
	 sprintf( bwb_ebuf, "in exp_ufnc(): expression returns number <%lf>",
	    (double) exp_getnval( e ) );
	 bwb_debug( bwb_ebuf );
	 }
#endif

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_ufnc(): single line after parsing, <%s>",
	 &( call_line->buffer[ epos ] ) );
      bwb_debug( bwb_ebuf );
#endif

      bwb_etov( v, e );
      bwb_decexec();
      }

   /* multi-line function must be executed now */

   else
      {

#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_ufnc(): found MULTI-LINE function" );
      bwb_debug( bwb_ebuf );
#endif

      /* now execute until function is resolved */

      bwb_execline();
      while( CURTASK exsc > save_elevel )
	 {
	 bwb_execline();
	 }

      /* find the return value */

      for ( r = c->local_variable; r != NULL; r = r->next )
	 {
	 if ( strcmp( r->name, c->name ) == 0 )
	    {
	    v = r;
	    }
	 }

      }

   /* now place value in expression stack */

   CURTASK exps[ CURTASK expsc ].type = (char) v->type;
   CURTASK exps[ CURTASK expsc ].pos_adv = position;

   switch( v->type )
      {
      case STRING:
	 CURTASK exps[ CURTASK expsc ].operation = CONST_STRING;

#if INTENSIVE_DEBUG
	 sprintf( bwb_ebuf, "in exp_ufnc(): ready to assign <%d>-byte STRING",
	    var_getsval( v )->length );
	 bwb_debug( bwb_ebuf );
#endif

	 str_btob( exp_getsval( &( CURTASK exps[ CURTASK expsc ] )),
	    var_getsval( v ) );

#if INTENSIVE_DEBUG
	 str_btoc( tbuf, var_getsval( v ) );
	 sprintf( bwb_ebuf, "in exp_ufnc(): string assigned <%s>", tbuf );
	 bwb_debug( bwb_ebuf );
#endif

	 break;

      default:
	 CURTASK exps[ CURTASK expsc ].operation = NUMBER;
	 CURTASK exps[ CURTASK expsc ].nval = var_getnval( v );
	 break;
      }

   return TRUE;

   }

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

	FUNCTION:       fslt_addlocalvar()

	DESCRIPTION:    This function adds a local variable
			to the FUNCTION-SUB lookup table at
			a specific level.

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

#if ANSI_C
int
fslt_addlocalvar( struct fslte *f, struct bwb_variable *v )
#else
int
fslt_addlocalvar( f, v )
   struct fslte *f;
   struct bwb_variable *v;
#endif
   {
   struct bwb_variable *c, *p;
#if INTENSIVE_DEBUG
   register int i;
#endif

   /* find end of local chain */

   if ( f->local_variable == NULL )
      {
#if INTENSIVE_DEBUG
      i = 0;
#endif
      f->local_variable = v;
      }
   else
      {
#if INTENSIVE_DEBUG
      i = 1;
#endif
      p = f->local_variable;
      for ( c = f->local_variable->next; c != NULL; c = c->next )
         {
         p = c;
#if INTENSIVE_DEBUG
         ++i;
#endif
         }
      p->next = v;
      }

   v->next = NULL;

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in fslt_addlocalvar(): added local variable variable <%s> arg number <%d>",
      v->name, i );
   bwb_debug( bwb_ebuf );
   getchar();
#endif

   return TRUE;

   }

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

	FUNCTION:       fslt_init()

	DESCRIPTION:    This function initializes the FUNCTION-SUB
			lookup table.

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

#if ANSI_C
int
fslt_init( int task )
#else
int
fslt_init( task )
   int task;
#endif
   {
   LOCALTASK fslt_start.next = &(LOCALTASK fslt_end);
   return TRUE;
   }

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

	FUNCTION:       is_label()

	DESCRIPTION:    This function determines whether the string
			pointed to by 'buffer' is a label (i.e.,
			ends with colon).

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

#if ANSI_C
extern int
is_label( char *buffer )
#else
int
is_label( buffer )
   char *buffer;
#endif
   {

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in is_label(): check element <%s>", buffer );
   bwb_debug( bwb_ebuf );
#endif

   if ( buffer[ strlen( buffer ) - 1 ] == ':' )
      {
      return TRUE;
      }
   else
      {
      return FALSE;
      }

   }