OpenEuphoria

Re: goto considered essential, revisited

• Posted by Igor Kachan <kinz at peterlink.ru> Jan 22, 2006
• 437 views

Tom Dailey wrote:
> 
> 
> This conversation seems to be wandering away from my original
> point. I am NOT advocating the addition of the goto statement
> to Euphoria. In my 38 years of experience as a systems
> programmer, I have seen much confusion caused by the unrestricted
> use of goto statements (or, before 1977, branch instructions), 
> and I have spent literally thousands of hours untangling and 
> rewriting the resulting spaghetti code.  What I AM advocating is 
> the addition of a very constrained control flow construct that 
> will allow graceful coding of abnormal procedure returns, AND 
> NOTHING ELSE. Please read the following code carefully.
> 
>     function    copyfile
>     (
>         sequence    input_file_name
>         sequence    output_file_name
>     )
>         integer     input_file_nr
>         integer     output_file_nr
>         object      line
>    
>         input_file_nr = open ( input_file_name, "r" )
>         exception cant_open_input_file if input_file_nr = -1
>         output_file_nr = open ( output_file_name, "w" )
>         exception cant_open_output_file if output_file_nr = -1
>         while 1 do
>             line = gets ( input_file_nr )
>             exit if atom ( line )
>             puts ( output_file_nr, line )
>         end while
>         close ( input_file_nr )
>         close ( output_file_nr )
>         return outcome__success
>         --
>         -- Exception handlers must follow the main body of 
>         -- the function or procedure. They are ONLY executed
>         -- via an exception statement in the main body.
>         --
>         when cant_open_input_file do
>             return outcome__cant_open_input_file
>         when cant_open_output_file do
>             close ( input_file_nr )
>             return  outcome__cant_open_output_file
>    
>     end procedure -- copyfile
> 
> In considering this code, remember that, in a real world case,
> a function might detect 5 or 6 abnormal conditions, and, for
> each one, need to perform several cleanup actions before returing
> an appropriate error code. The proposed exception handling
> construct is merely a disciplined mechanism for removing such
> actions from the main (non-error) logic, with the intent of 
> making that logic easier to read.
> 
> Tom


Hello Tom,

Try please:

     function    copyfile
     (
         sequence    input_file_name
         sequence    output_file_name
     )
         integer     input_file_nr
         integer     output_file_nr
         object      line
    
         input_file_nr = open ( input_file_name, "r" )
--         exception cant_open_input_file if input_file_nr = -1
  if input_file_nr = -1 then 
      return outcome__cant_open_input_file 
  end if
         output_file_nr = open ( output_file_name, "w" )
--         exception cant_open_output_file if output_file_nr = -1

  if output_file_nr = -1 then 
      close(input_file_nr) 
      return outcome__cant_open_output_file 
  end if

         while 1 do
             line = gets ( input_file_nr )
             exit if atom ( line )
             puts ( output_file_nr, line )
         end while
         close ( input_file_nr )
         close ( output_file_nr )
         return outcome__success
--         --
--         -- Exception handlers must follow the main body of 
--         -- the function or procedure. They are ONLY executed
--         -- via an exception statement in the main body.
--         --
  --       when cant_open_input_file do
    --         return outcome__cant_open_input_file
      --   when cant_open_output_file do
        --     close ( input_file_nr )
          --   return  outcome__cant_open_output_file
   
    end function  -- procedure -- copyfile

You can do it just now, program can *jump* from *any* point of a procedure
or a function body. Just put 'return' in a procedure, and 'return something'
in a function.

Same thing with loops - just put 'exit' and program jumps to the next
operator after 'end for' or 'end while'.  

Maybe I just do not understand your problem here ...

But these 'return' and 'exit' work good, at least in your example.
You can have many of these returns and exits in a body of every blok.

A single door to enter a room but as many windows as you wish to
jump out, so to say.

Good Luck!

HTH.

Regards,
Igor Kachan
kinz at peterlink.ru