[slang-users] try does not run require

[John E. Davis]

Jörg Sommer <joerg at alea.gnuu.de> wrote:
>Have you ever written a language specification for SLang? Something with
>a grammar and a definition of the scope of variables? I can't construct

  slang/doc/grammar.txt specifies the grammar, although it may be
  somewhat incomplete.  Variables are either global, local to a
  namespace or file, or local to a function.  I have not added, and
  probably will not add block-local variables.

>an example, but I have seen code like this that failed, because a
>variable of the same name is defined.
>
>#v+
>do
>{
>    variable foo = 2;
>    message("bla");
>}
>while (0);
>
>variable foo = 3;

Right-- as stated above the variable in the do-while loop shares the
same scope as the latter declaration.  Someday I _may_ add block-local
variables, but probably not because I have seen them abused too much
in C to the point that some code is no longer easily maintainable.
Some C programmers may be tempted to write

   variable i;
   variable j = 0;
   for (i = 0; i < n; i++)
     {
         variable j;
         for (j = 0; j < M; j++) ...
     }

and would be suprised to find that j is not 0 at the end of this code
fragment.  For this reason, slang flags the duplicate declaration of j
as an error.  But it only generates this error when the code occurs
in a function.  It does not do so for global variables, so that code
such as

    if (0 == is_defined ("Some_Variable"))
      variable Some_Variable = Some_Default_Value;

may be used in a file to permit customization by a user.  You can
think of this as something akin to jed's custom_variable function.

--John