bwb_elx.c

这是一个简易的basic语言解释器, 可供我们学习和改进.

         default:                               /* anything else */
            loop = FALSE;
            paren_level = 0;                    /* do not look for arguments */
            break;
         }
      }

   /* find arguments within parentheses */
   /* for each argument, find a string ending with ',' or with end parenthesis */

   n_args = 0;
   s_pos = 0;
   CURTASK exps[ CURTASK expsc ].string[ 0 ] = '\0';

   while( paren_level > 0 )
      {

      /* check the current character */

      switch( expression[ CURTASK exps[ CURTASK expsc ].pos_adv ] )
         {

         case ',':                      /* end of an argument */

            if ( paren_level == 1 )     /* ignore ',' within parentheses */
               {

               /* call bwb_exp() recursively to resolve the argument */

               if ( exp_validarg( CURTASK exps[ CURTASK expsc ].string ) == TRUE )
                  {
#if INTENSIVE_DEBUG
		  sprintf( bwb_ebuf,
		     "in exp_function(): valid argument (not last)." );
                  bwb_debug( bwb_ebuf );
#endif

                  CURTASK exps[ CURTASK expsc ].rec_pos = 0;
                  e = bwb_exp( CURTASK exps[ CURTASK expsc ].string, FALSE,
                     &( CURTASK exps[ CURTASK expsc ].rec_pos ) );

                  /* assign operation and value at this level */

                  var_make( &( argv[ n_args ] ), e->type );

                  switch( argv[ n_args ].type )
                     {
                     case NUMBER:
                        * var_findnval( &( argv[ n_args ] ), argv[ n_args ].array_pos )
                            = exp_getnval( e );
                        break;
                     case STRING:
                        str_btob( var_findsval( &( argv[ n_args ] ),
                           argv[ n_args ].array_pos ), exp_getsval( e ) );
                        break;
                     }

                  ++n_args;                /* increment number of arguments */

                  }

               s_pos = 0;               /* reset counter */
               CURTASK exps[ CURTASK expsc ].string[ 0 ] = '\0';
               }

            else
               {
               CURTASK exps[ CURTASK expsc ].string[ s_pos ]
                  = expression[ CURTASK exps[ CURTASK expsc ].pos_adv ];
               ++s_pos;
               CURTASK exps[ CURTASK expsc ].string[ s_pos ] = '\0';
               }
            break;

         case '(':
            ++paren_level;
            CURTASK exps[ CURTASK expsc ].string[ s_pos ]
               = expression[ CURTASK exps[ CURTASK expsc ].pos_adv ];
            ++s_pos;
            CURTASK exps[ CURTASK expsc ].string[ s_pos ] = '\0';
            break;

         case ')':
            --paren_level;

#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf,
               "in exp_function(): hit close parenthesis." );
            bwb_debug( bwb_ebuf );
#endif

            if ( paren_level == 0 )
               {

#if INTENSIVE_DEBUG
               sprintf( bwb_ebuf,
                  "in exp_function(): paren level 0." );
               bwb_debug( bwb_ebuf );
#endif

               /* call bwb_exp() recursively to resolve the argument */

               if ( exp_validarg( CURTASK exps[ CURTASK expsc ].string ) == TRUE )
                  {
#if INTENSIVE_DEBUG
		  sprintf( bwb_ebuf,
		     "in exp_function(): valid argument (last)." );
		  bwb_debug( bwb_ebuf );
#endif

                  CURTASK exps[ CURTASK expsc ].rec_pos = 0;
                  e = bwb_exp( CURTASK exps[ CURTASK expsc ].string, FALSE,
                     &( CURTASK exps[ CURTASK expsc ].rec_pos ) );

#if INTENSIVE_DEBUG
		  sprintf( bwb_ebuf,
		     "in exp_function(): return from bwb_exp(), last arg, type <%c> op <%d>",
		     e->type, e->operation );
		  bwb_debug( bwb_ebuf );
#endif

                  /* assign operation and value at this level */

                  var_make( &( argv[ n_args ] ), e->type );

                  switch( argv[ n_args ].type )
                     {
                     case NUMBER:
                        * var_findnval( &( argv[ n_args ] ), argv[ n_args ].array_pos )
                            = exp_getnval( e );
                        break;
                     case STRING:
                        str_btob( var_findsval( &( argv[ n_args ] ),
                           argv[ n_args ].array_pos ), exp_getsval( e ) );
                        break;
                     }

                  ++n_args;                /* increment number of arguments */

                  }

               s_pos = 0;               /* reset counter */
               CURTASK exps[ CURTASK expsc ].string[ 0 ] = '\0';
               }

            else
               {
               CURTASK exps[ CURTASK expsc ].string[ s_pos ]
                  = expression[ CURTASK exps[ CURTASK expsc ].pos_adv ];
               ++s_pos;
               CURTASK exps[ CURTASK expsc ].string[ s_pos ] = '\0';
               }
            break;

         case '\"':                             /* embedded string constant */

            /* add the initial quotation mark */

            CURTASK exps[ CURTASK expsc ].string[ s_pos ]
               = expression[ CURTASK exps[ CURTASK expsc ].pos_adv ];
            ++s_pos;
            CURTASK exps[ CURTASK expsc ].string[ s_pos ] = '\0';
            ++CURTASK exps[ CURTASK expsc ].pos_adv;

            /* add intervening characters */

            while ( ( expression[ CURTASK exps[ CURTASK expsc ].pos_adv ] != '\"' )
               && ( expression[ CURTASK exps[ CURTASK expsc ].pos_adv ] != '\0' ) )
               {
               CURTASK exps[ CURTASK expsc ].string[ s_pos ]
                  = expression[ CURTASK exps[ CURTASK expsc ].pos_adv ];
               ++s_pos;
               CURTASK exps[ CURTASK expsc ].string[ s_pos ] = '\0';
               ++CURTASK exps[ CURTASK expsc ].pos_adv;
               }

            /* add the concluding quotation mark */

            CURTASK exps[ CURTASK expsc ].string[ s_pos ]
               = expression[ CURTASK exps[ CURTASK expsc ].pos_adv ];
            ++s_pos;
            CURTASK exps[ CURTASK expsc ].string[ s_pos ] = '\0';
            /* the following bracketed out 14 July 1992; since this counter */
            /* incremented at the end of the switch statement, this may */
            /* increment it past the next character needed */
            /* ++CURTASK exps[ CURTASK expsc ].pos_adv; */
            break;

         default:
            CURTASK exps[ CURTASK expsc ].string[ s_pos ]
               = expression[ CURTASK exps[ CURTASK expsc ].pos_adv ];
            ++s_pos;
            CURTASK exps[ CURTASK expsc ].string[ s_pos ] = '\0';
#if INTENSIVE_DEBUG
            sprintf( bwb_ebuf, "in exp_function(): new char <%d>=<%c>",
               expression[ CURTASK exps[ CURTASK expsc ].pos_adv ],
               expression[ CURTASK exps[ CURTASK expsc ].pos_adv ] );
            bwb_debug( bwb_ebuf );
            sprintf( bwb_ebuf, "in exp_function(): building <%s>.",
               CURTASK exps[ CURTASK expsc ].string );
            bwb_debug( bwb_ebuf );
#endif
            break;
         }

      /* advance the counter */

      ++CURTASK exps[ CURTASK expsc ].pos_adv;

      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_function(): ready to call function vector" );
   bwb_debug( bwb_ebuf );
#endif

   /* call the function vector */

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_function(): calling preset function" );
   bwb_debug( bwb_ebuf );
#endif

   v = CURTASK exps[ CURTASK expsc ].function->vector ( n_args, &( argv[ 0 ] ),
      CURTASK exps[ CURTASK expsc ].function->id );

   /*-------------------------------------------------*/
   /* Now free the argv memory                        */
   /* (some other less fortunate routine may need it) */
   /* JBV, 10/95                                      */
   /*-------------------------------------------------*/
   FREE( argv, "exp_function" );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_function(): return from function vector, type <%c>",
      v->type );
   bwb_debug( bwb_ebuf );
#endif

   /* assign the value at this level */

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

#if INTENSIVE_DEBUG
         sprintf( bwb_ebuf, "in exp_function(): ready to assign STRING" );
         bwb_debug( bwb_ebuf );
#endif

         b = var_findsval( v, v->array_pos );
         str_btob( exp_getsval( &( CURTASK exps[ CURTASK expsc ] )), b );

#if INTENSIVE_DEBUG
         str_btoc( tbuf, b );
         sprintf( bwb_ebuf, "in exp_function(): 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;
      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_function(): end of function" );
   bwb_debug( bwb_ebuf );
#endif

   /* return */

   return TRUE;

   }

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

	FUNCTION:       exp_variable()

	DESCRIPTION:    This function interprets a variable.

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

#if ANSI_C
int
exp_variable( char *expression )
#else
int
exp_variable( expression )
   char *expression;
#endif
   {
   int pos;
   int *pp;
   int n_params;
   register int n;
   struct bwb_variable *v;
   bstring *b;
   int p;

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

   /* get the variable name */

   exp_getvfname( expression, CURTASK exps[ CURTASK expsc ].string );

   /* now find the variable itself */

   v = CURTASK exps[ CURTASK expsc ].xvar = var_find( CURTASK exps[ CURTASK expsc ].string );

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_variable(): level <%d>, found variable name <%s>",
      CURTASK expsc, CURTASK exps[ CURTASK expsc ].xvar->name );
   bwb_debug( bwb_ebuf );
#endif

   /* note that this level is a variable */

   CURTASK exps[ CURTASK expsc ].operation = VARIABLE;

   /* read subscripts */

   pos = strlen( CURTASK exps[ CURTASK expsc ].string );
   if ( ( v->dimensions == 1 ) && ( v->array_sizes[ 0 ] == 1 ))
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_variable(): variable <%s> has 1 dimension",
         CURTASK exps[ CURTASK expsc ].xvar->name );
      bwb_debug( bwb_ebuf );
#endif
      pos = strlen( v->name );
      n_params = 1;
      pp = &p;
      pp[ 0 ] = dim_base;
      }
   else
      {
#if INTENSIVE_DEBUG
      sprintf( bwb_ebuf, "in exp_variable(): variable <%s> has > 1 dimensions",
         CURTASK exps[ CURTASK expsc ].xvar->name );
      bwb_debug( bwb_ebuf );
#endif
      dim_getparams( expression, &pos, &n_params, &pp );
      }

   CURTASK exps[ CURTASK expsc ].pos_adv = pos;
   for ( n = 0; n < v->dimensions; ++n )
      {
      CURTASK exps[ CURTASK expsc ].array_pos[ n ] = v->array_pos[ n ] = pp[ n ];
      }

#if INTENSIVE_DEBUG
   for ( n = 0; n < v->dimensions; ++ n )
      {
      sprintf( bwb_ebuf, "in exp_variable(): var <%s> array_pos element <%d> is <%d>.",
         v->name, n, v->array_pos[ n ] );
      bwb_debug( bwb_ebuf );
      }
#endif

   /* assign the type and value at this level */

   CURTASK exps[ CURTASK expsc ].type = (char) v->type;
   
   switch( v->type )
      {
      case STRING:
         b = var_findsval( v, v->array_pos );
#if TEST_BSTRING
         sprintf( bwb_ebuf, "in exp_variable(): b string name is <%s>",
            b->name );
         bwb_debug( bwb_ebuf );
#endif
#if OLDWAY
	 CURTASK exps[ CURTASK expsc ].sval.length = b->length;
	 CURTASK exps[ CURTASK expsc ].sval.sbuffer = b->sbuffer;
#endif
	 str_btob( &( CURTASK exps[ CURTASK expsc ].sval ), b );
         break;
      default:
         CURTASK exps[ CURTASK expsc ].nval = var_getnval( v );
         break;
      }

#if INTENSIVE_DEBUG
   sprintf( bwb_ebuf, "in exp_variable(): exit, name <%s>, level <%d>, op <%d>",
      v->name, CURTASK expsc, CURTASK exps[ CURTASK expsc ].operation  );
   bwb_debug( bwb_ebuf );
#endif

   /* return */

   return TRUE;

   }