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+//###########################################################-*-outline-*-####
+// TODO list
+//############################################################################
+// $Id$
+
+* Histories
+
+  Requires: -
+
+  Create a class "History<X>" that can be used to store a phase
+  dependent value of type "X". We can then have TypeHistories,
+  FlagHistories, ClosureHistories, ...
+
+  Currently only symbols may contain phase dependent values. For that
+  reason we sometimes create symbols just because we need a phase
+  dependent type (for example the thisTypeSym). And sometimes we don't
+  have phase dependent values where we should (for example lobound in
+  AbsTypeSymbol or flags in Symbol)
+
+  Once we have histories, it is possible to add one or several
+  phase-dependent values to every symbol (and also to other data
+  types).
+
+  The two base operations of class "History" are "getValueAt(Phase)"
+  and "setValueAt(Phase)". There are two kinds of histories: those
+  that may only return values already set and those that trigger the
+  evaluation of values not yet set (=> lazy types).
+
+
+* Remove the notion of primary constructor.
+
+  Requires: Histories
+
+  In case of abstract types and type aliases, the sole purpose of the
+  primary constructor is to store the type parameters. These type
+  parameters can be stored in a type parameters history.
+
+  In case of class types, the primary constructor stores the type and
+  value parameters of the class and it defines a valid instance
+  constructor. As for abstract types and type aliases, the type and
+  value parameters can be stored in parameters histories and the
+  instance constructor defined be the primary constructor can be
+  replaced by a normal constructor.
+
+
+* Remove symbols from MethodTypes and PolyTypes
+
+  Requires: Histories, Primary constructor removal
+
+  The symbols of the value parameters of methods are currently stored
+  in their type in "MethodType" types. These symbols can be stored in
+  a new parameters history of class "TermSymbol". The array of symbols
+  in the "MethodType" type can then be replaced by an array of types.
+
+  The process is about the same for symbols in PolyTypes. The main
+  difference is that type parameters may be referenced and thus we
+  need something like De Bruijn indicies to represent these
+  references.
+
+
+* Scopes with history
+
+  Requires: -
+
+  Implement scopes that maintain a validity phase interval for each of
+  its member. Members may then only be added to scopes. Removing is
+  replaced by terminating the validity interval.
+
+
+* Implement a type IntervalType(Type,Type)
+
+  Requires: -
+
+  A type IntervalType(Type,Type) specifies an upper and a lower
+  bound. This type can be used to replace the loBound field in class
+  AbsTypeSymbol. It makes it possible to merge classes TypeAliasSymbol
+  and AbsTypeSymbol into one single class whose info is either a
+  TypeRef for type aliases or an IntervalType for abstract types.
+
+
+* Solve refinement problem.
+
+  Requires: Histories, Scopes with history, IntervalTypes
+
+  Replace the current type CompoundType(Type[],Scope) by the new types
+  CompoundType(Type[]) and RefinementType(Type,Map<Symbol,Type>) and
+  add a Scope field in class ClassSymbol.
+
+  Replace the symbol in compound types by a closure history.
+
+//############################################################################