Re: [slang-users] new slang 2 development snapshot released

[Michael Noble <mnoble@xxxxxxxxxxxxx>]

> John, what we be required for s-lang to "verify" code syntax snippets.
> 
> This would help out tremendously with my SLAG project, since I will be
> storing "functions" in files along with the display/print items ...

Below is what I use in VWhere (visual 'where, bundled with SLgtk) to 
validate expressions users have typed into a text window.  It consists
of an ERROR_BLOCK in S-Lang scope, and 2 C functions (one registered
as S-Lang intrinsic).

I think the exception handling mechanisms in SLang2 will make this
kind of stuff cleaner and more robust.

Cheers,
-Mike

-----------------------------------------------------------------------

   ERROR_BLOCK
   {
	_clear_error();
	_toggle_error_hook();
	return vw_echo_status(vwd,
		sprintf("could not evaluate expression: %s",expr),NULL);
   }

   % Custom error hook, to enable recovery from normally unrecoverable errs
   variable nargs = _stkdepth();
   _toggle_error_hook();
   eval(expr);
   _toggle_error_hook();

The toggle function is a C intrinsic, and looks something like

   static void recover_unrecoverable_error_hook(char *error_msg)
   {
      fputs(error_msg,stderr);	/* support function, which lets scripts */
      fputs("\r\n", stderr);	/* catch "unrecoverable" errors within  */
      fflush (stderr);		/* an ERROR_BLOCK */
      SLang_restart(0);
      SLang_set_error(SL_USAGE_ERROR);
   }

  static void toggle_error_hook(void)
  {
	static void (*previous_error_hook)(char *);

	if (SLang_Error_Hook == recover_unrecoverable_error_hook)
	   SLang_Error_Hook = previous_error_hook;
	else {
	   previous_error_hook = SLang_Error_Hook;
	   SLang_Error_Hook = recover_unrecoverable_error_hook;
	}
  }

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