INTERFACE StackTbl;

IMPORT Atom;

TYPE
  T <: Public;
  Public = OBJECT
    next_index: CARDINAL;
    next_formal: INTEGER
  METHODS
    init(): T;
  END;

A newly allocated StackTbl.T must be initialized before use, and can be initialized again for re-use. A newly intialized StackTbl.T has a next_index of 1, a next_formal of -1, and an empty list.

PROCEDURE Mark(t: T);

Add a mark to the front of t's list.

PROCEDURE PopToMark(t: T);

Remove all entries from t's list up to and including the first mark. This call should ``balance'' with a previous call to Mark. More precisely, it is a checked run-time error to call this procedure if t's stack does not contain any marks.

PROCEDURE Push(t: T; nm: Atom.T);

Add the pair (nm, t.next_index) to the front of t's list, and increment t.next_index.

PROCEDURE PushFormal(t: T; nm: Atom.T);

Add the pair (nm, t.next_formal) to the front of t's list, and decrement t.next_formal.

PROCEDURE Lookup(t: T; nm: Atom.T): INTEGER;

Return the integer paired with the first occurrence of nm in t's list, or return 0 if there are no such occurrences.

END StackTbl.