Re: bug(?) in black3 and Guido Gonzato's updates

["John E. Davis" <davis@xxxxxxxxxxxxx>]

Jörg Sommer <joerg@xxxxxxxxxxxx> wrote:
> Yes, me too. I thought it was the effect of a change anywhere else,
> because black3.sl doesn't define keyword and keyword1. From which
> color table these settings are inherited?

These keywords are in the defined in the file:

  # grep keyw black3.sl
  set_color("keyword", "brightred", $2); % if, while, unsigned, ...
  set_color("keyword1", "green", $2);    % malloc, exit, etc...
  set_color("keyword2", $1, $2);
  set_color("keyword3", $1, $2);
  set_color("keyword4", $1, $2);
  set_color("keyword5", $1, $2);
  set_color("keyword6", $1, $2);
  set_color("keyword7", $1, $2);
  set_color("keyword8", $1, $2);
  set_color("keyword9", $1, $2);

> Oh, I've thought the equivalent code is insert_spaces (--goal, goal), but
> you are the developer of S‐Lang and you are right. Thanks for reviewing
> these patches.

I think the confusion arises because slang and C differ here.  In C,
all statements, including assignment statements, produce a value.  For
example, in C

   x = (foo = bar);

is equivalent to 

   foo = bar;
   x = bar;

because foo=bar will evaluate to bar. In contrast, in S-Lang 
x=(foo=bar) will generate a StackUnderflow exception, since foo=bar
does not produce a value that can be assigned to x.  

This also means that C distingushes between X++ and ++X:
   
   X = 1;
   Y = X++;  ==> Y=1, X=2;
   
   X = 1;
   Y = ++X;  ==> Y = 2, X=2;

However, since X++ does not produce a value in S-Lang, there is no
difference between X++ and ++X.  This also means that in S-Lang one
cannot use the commmon idiom:

    i = 10;
    while (i--) { ... }

Instead, the above can be written in S-Lang using:

    i = 10;
    while (i, i--) { ... }

Hopefully the S-Lang documentation adequately explains these
differences.

Thanks,
--John

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