[Fenfire-dev] PEG: pure node functions

[Tuomas Lukka]

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PEG purenodefunction--tjl: 
=============================================================

:Author:   Tuomas J. Lukka
:Last-Modified: $Date: 2003/08/17 13:52:46 $
:Revision: $Revision: 1.1 $
:Status:   Incomplete

The NodeFunction framework is misused in several places
in Fenfire, as there are lots of node functions for
which the invariants do not hold.

This PEG suggests a way forwards to both not require too
great changes to current code but allow pure functional
semantics to be specified and applied.

Issues
======

Changes
=======

Add a new interface, ``PureNodeFunction`` as a subinterface
of NodeFunction.

It defines no methods but explicitly defines the invariant.

CachedNodeFunction shall only accept PureNodeFunctions.

PureNodeFunction-implementing classes SHALL BE IMMUTABLE -
all members will be final. Changing members will work
by creating a new instance with a changed member.