OpenEuphoria

Re: goto considered essential, revisited

• Posted by Igor Kachan <kinz at peterlink.ru> Jan 23, 2006
• 465 views

Igor Kachan wrote:

[snip]

> 
> Hello Tom,
> 
> Try please:
> 
> }}}
<eucode>
> 
>      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
> 
> </eucode>
{{{

> 
> 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.

Hello again Tom,

Let me to offer more refined version of the above function.
It is rewritten in pure EU code now, not in pseudocode,
and as I like to see it, just as example - to really copy a file,
the 'system' command may be better:

-- file.exu
  function copy_text_file(
	      sequence in,  -- name of the input file
	     sequence out)  -- name of the output file

	  integer in_fn, out_fn -- the file numbers
	   object line -- the buffer string
     
	  in_fn = open(in, "r")

   if in_fn = -1 then -- can not open the input file
       return -1      -- code for bad input file
   end if 

	out_fn = open(out, "w")

   if out_fn = -1 then  -- can not open the output file,
       close(in_fn)     -- but input file it open already
	return -2       -- code for bad output file
   end if
 
	  while 1 do
	      line = gets(in_fn)
		  if sequence(line) then
		     puts(out_fn, line)
		  else  
		     close(in_fn )
		     close(out_fn)
		     return 1 -- code for success
		  end if   
	  end while
   end function -- copy_text_file()
    
   integer i
    
   i= copy_text_file("file.exu","file.exuu")
    
   ? i
-- end of file.exu

See please, inside a subprogram, program can jump from the loop
body just with the 'return' command too, if it is a convenient
jump for your function or procedure. 

To be without 'goto', Euphoria has the very clear and very flexible
syntax, be sure. Just try it to do what you want.

Good Luck!

Regards,
Igor Kachan
kinz at peterlink.ru