[Cuis] Left arrow and up arrow characters

[David Graham]

One of the first things that I noticed in Cuis, was that it uses left 
arrow for assignment and up arrows for return, just like what you see in 
the Blue Book(1).  I ran into a small problem with my "legacy" :) file 
naming standard ( underscores for separation ) and Juan helped me out 
with the following bit of advice:

>  Simply evaluating 'StrikeFont useUnderscore'displays the ASCII ^ and _
>  glyphs. If you ever want to go back to left and up arrow, evaluate
>  'StrikeFont useLeftArrow'. I included both sets of glyphs so everybody can
>  choose.

>  Please note that this doesn't affect the parser. In any case both _ and :=
>  are valid for assignment, but not for use in selectors or variable names.
>  Preferences #allowUnderscoreSelectors and #allowUnderscoreAssignments give
>  you some control over this. If you set #allowUnderscoreSelectors to true
>  and #allowUnderscoreAssignments to false, you get the standard behavior in
>  many Smalltalks, where the underscore can be part of selectors or variable
>  names. In this case, if you modify existing methods, you need to change
>  assignments to be := so they will compile.


I was little curious why the smalltalk creators picked those characters 
and discovered that the left arrow was used for assignment in Xerox's 
Mesa language, and in turn the Xerox Alto computer had a key with a left 
arrow.  Choosing these for smalltalk is obvious when you see the keyboard:


More pictures of the Alto can be found here (use the zoom feature to get 
a closeup of the keyboard):
http://www.computerhistory.org/revolution/input-output/14/347/1520?position=0



(1) http://stephane.ducasse.free.fr/FreeBooks/BlueBook/
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