package Symbol_Table is

-- DESCRIPTION :
--   This package provides management of a table of symbols, useful
--   in the input/output of polynomials in several variables.

-- AUXILIARY DATA STRUCTURES :

  subtype Symbol is string(1..5);

-- EXCEPTIONS :
    
    OVERFLOW_IN_THE_SYMBOL_TABLE : exception;
     -- occurs when a new symbol is added to a full symbol table

    INDEX_OUT_OF_RANGE : exception;
     -- occurs when a symbol is asked that is not in the range of the table

-- CREATORS :

  procedure Init ( max : in natural );

  -- DESCRIPTION :
  --   A new symbol table is created with place for max symbols.

  procedure Enlarge ( max : in natural );

  -- DESCRIPTION :
  --   Enlarges the symbol table so that it can contain as many symbols
  --   as the previous maximum plus the new max.

  procedure Replace ( i : in natural; sb : in Symbol );

  -- DESCRIPTION :
  --   Replaces the ith symbol by the given sb.

-- CONSTRUCTORS :

  procedure Add ( sb : in Symbol );
  procedure Add ( sb : in Symbol; pos : out natural );

  -- DESCRIPTION :
  --   A new symbol is added to the symbol table;
  --   pos is the entry of the added symbol in the table.

  procedure Remove ( sb : in Symbol );
  procedure Remove ( i : in natural );

  -- DESCRIPTION :
  --   Removes the ith symbol sb from the symbol table.

-- SELECTORS :

  function "<" ( s1,s2 : Symbol ) return boolean;
  function ">" ( s1,s2 : Symbol ) return boolean;

  -- DESCRIPTION :
  --   Defines an order relation on the symbols.

  function Maximal_Size return natural;

  -- DESCRIPTION :
  --   Returns the maximal number of symbols the table can contain.

  function Number return natural;
    
  -- DESCRIPTION :
  --   Returns the number of current symbols in the table.

  function Empty return boolean;

  -- DESCRIPTION :
  --   Returns true if the symbol table has not been initialized yet,
  --   or if a Clear has been done.

  function Get ( sb : Symbol ) return natural;

  -- DESCRIPTION :
  --  The entry of the symbol in the table is returned.
  --  If the symbol does not occur in the table, then 0 is returned.

  function Get ( i : natural ) return Symbol;

  -- DESCRIPTION :
  --   The symbol corresponding with the ith unknown is returned.

-- DESTRUCTOR :

  procedure Clear;
  
  -- DESCRIPTION :
  --   The allocated memory space is freed.

end Symbol_Table;