Re: Some questions

["John E. Davis" <davis>]

Joerg Sommer <joerg@xxxxxxxxxxxx> wrote:
>is !if (foo) faster then if (foo != 0) or why exists this version of
>negation?

The first form is twice as fast:

jdl> x = 0; tic; loop (10000000) !if (x); toc;
1.92
jdl> x = 0; tic; loop (10000000) if (x!=0); toc; 
4.06

(jdl is my version of IDL--- a S-Lang-based interactive data language)

>How to declare a variable read only? slang.txt tells, that read only
>variables are possible, but doesn't say how.

Only intrinsic variables may be made readonly.  S-Lang 2 _may_ support
user defined constants.

>What does ".[var]"? (var is a variable) I found it in site.sl
>custom_variable().

The first version of S-Lang used a reverse polish syntax resembling
postscript.  This syntax is still supported, though not recommended.
Using this syntax, it is possible to write

   define foo (x)
   {
      return x + 1;
   }

as:

   . ( [x] =x x 1 + ) foo


Take a look at jed/lib/dcl.sl for a more extensive example of this
syntax.

>And what's with %!%+ and %!%-? Are this active comments? Where can I read
>more about them? How to use them? Is there a function in jed, that helps
>creating them?

These are documentation markers that are processed using sl2tm
distributed with slang in the 

   slang/doc/tm/tools/

directory.  See also jed/doc/tm/* for more information.

--John

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