SQL Server 2005 - Using the derived value in the Select WHERE Condition

Select  field a, field b,
  GetSomelList(tableA.field z) as Lista,   /* Where GetSomeList is a function
field c
from  tableA 
where  some condition AND  Lista <> ','
 
I get the error Lista is not a "table column' as expected because it is dervied 
 value and not a table column.
 
I can do this
 
Select  field a, field b,
  GetSomelList(tableA.field z) as Lista,  /* Where GetSomeList is a function
field c
from  tableA 
where  some condition AND  GetSomelList(tableA.field z)  <> ','
 
Is there a better way of do this  instead of calling the same function twice in the select statement.

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