[e-lang] Two-vat figure

[Ka-Ping Yee]

I've posted a new design for the two-vat figure at

    http://zesty.ca/2vat.png

(This is a revision of the original figure on page 9 of
https://www.cypherpunks.to/erights/talks/promises/promises2.pdf .)

(There is a corresponding one-vat figure at: http://zesty.ca/1vat.png .)

The changes and their corresponding motivations are as follows:

    1.  The diagram is rearranged to read mostly left to right, instead
        of bottom-right to bottom-left to top-right.  Reasoning:
        left-to-right reading order is more natural.

    2.  The stack and queue are integrated into the structure of the vat.
        Reasoning: they are a part of the way the vat works, so they
        shouldn't look like other objects just floating around in the vat.

    3.  The vats and objects are given non-cryptic names.  Reasoning:
        words are easier to understand than abbreviations like XL.
        (Mark, i know you said you preferred not to do this.  We can
        change it back if you want, but i wanted to at least show what
        i originally had in mind.)

    4.  The sequence of steps is labelled in a distinct style (white
        on black filled circles).  Reasoning: the sequence of steps
        should draw the eye.

    5.  Descriptions are added to steps 2, 4, and 5.  Reasoning: an
        explanation helps show what is going on here; the message
        names in the original figure aren't enough.

    6.  Dotted arrows are added to show the eventual message being
        placed on the queue and removed from the queue for processing.
        Reasoning: without these arrows, it looks like the message is
        being delivered immediately.  The arrows also make it clear
        that the message arriving, the message on the queue, and the
        message being delivered are one and the same message.  (In
        the original there is no clear cue that the message on the
        queue is the message on the incoming pointer.)

    7.  The number 33 is moved inside the message arrow.  Reasoning:
        too many arrows produce visual clutter.  The 33 is a selfless
        value, so the semantics are unchanged, the diagram is clearer,
        and the messages containing 33 also appear more distinct.

    8.  The message arrows now point right instead of left.  Reasoning:
        this makes more sense with the left-to-right reading order
        since the messages travel from left to right.

    9.  The shapes of the message arrows are simplified.  Reasoning:
        this makes the diagram clearer by reducing the number of visual
        elements and also makes more room for the contents (33).

My goal here is to put enough information in the diagram so that even
a casual reader whose eyes happen to land on the figure while skimming
over the document has a decent chance of figuring out the story, and
may then be enticed to read the details in the text.

These 1-vat and 2-vat figures shade the stack and queue areas of the
vat.  If it's really necessary for Springer the shading could be
removed and replaced with partition lines, but shading is a better
option when possible since the extra lines generate unnecessary visual
clutter and line crossings.


-- ?!ng