Restriction on buyprice/sellprice being foreign

["giggollo99" <giggollo@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>]

Hi,

Im trying to simulate trading instrument A based on the price action 
of instrument B. To do this, i write all the code normally for 
instrument B, then i just set the 
buyprice/sellprice/shortprice/coverprice arrays to the prices of 
symbol A. However, the backtest gives prices based on symbol A's data 
even though im setting the buyprice/sellprice/shortprice/coverprice to 
FOREIGN function.

Is there any restriction on buyprice/sellprice/shortprice/coverprice 
being set to a FOREIGN function?