Inter-Office Memorandum
    To          Interpress Interest    Date    December 29, 1982
    From    Doug Wyatt        Location    Palo Alto
    Subject    Implementing Interpress    Organization    PARC/ISL
    XEROX
    Filed on:    [Indigo]<Interpress>IPImpl.Tioga and IPImpl.Interpress
    Uses:    [Indigo]<Interpress>Styles>Interpress.Style and Cedar.Style
    Implementing Interpress
    Introduction
        Introduction goes here.
        If you are looking at this document on-line, you might want to use the level-clipping function to see the overall structure rather 
        than simply plowing straight through.  Hit the "Levels" button in the top menu, then hit "FirstLevelOnly" in the new menu 
        that appears.  That will show you the major section headings.  Hit "MoreLevels" to see the subsections, or hit "AllLevels" 
        to read the details.
    Cedar vs. Mesa
    Type representation
        Types Any, Mark, Body, other stuff (Block, Page).
    Storage management
        Worry about multiple instances?
    Encodings
    The skeleton
    Handling {} and []
    The base language
    State
        Allow for multiple instances of the interpreter running in parallel. Example: several windows displaying Interpress documents.
    The stack
        Linked list or array? Impact on the implementation of ROLL.
    Frames and Contexts
        Note that frames must be copied; one might be tempted to use the pool mechanism to restore values overwritten by FSET, but this 
        will not suffice. For example, consider an Operator that calls itself recursively.
        One useful optimization for frames: don't copy until the first FSET.
    Errors
        Carefully define what happens when an UNMARK0 causes an error.
    The imager
    Imager variables
        Saving and restoring persistent and non-persistent variables. Is the mechanism general enough for arbitrary Pools? What's special 
        about the Transformation T? What should be cached?
    Sampled masks and the cache
        Clipper must note whether a sampled mask has been clipped.
    Priority
    Handling IFCOPY
        How does IFCOPY interact with priorityImportant?
    PD files
    The printing engine
    Performance