Perform a table based lookup
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 Syntax

        H_Lookup( cValue, cDBName , trow , tcol , brow , bcol , ;
                  drow , dcol, bReturn , bFunction , aKeyDesc , aGetExitKeys )

 Arguments:

      cValue    - Initial value of lookup code
      cDBName   - Alias of table to be looked up
      tRow      - Row of field
      tCol      - Column of field
      bRow      - Bottom row of box
      bCol      - Right column of box
      dRow      - Top row of box (defaults to tRow)
      dCol      - Left column of box (defaults to tCol)
      bReturn   - Code block to return value
      bFunction - Code block to evaluate before exit
      aKeyDesc  - Array of key codes and descriptions
      aGetExitKeys - Keys that will cause an exit from the GET

 Returns:

      NIL

 Description:

      Performs a lookup on values in a table.  The table must have two
      fields - the first should be a lookup code, and the second should be
      a description field.

 Examples:



 Header File: H_LIB52.CH

 Source: LOOKUP.PRG

 Author:  Martin Colloby