OpenEuphoria

1. ex.exe hangs in a while loop

• Posted by olddog <halletts at sasktel.net> Jul 12, 2006
• 528 views

My 2.5 interpreter hangs (even the trace() debugger hangs) with this code:

incude get.e
procedure main()
  integer crsr, price
  sequence text, t
  text = "/GRVY $.75 /GRVY $.75"
  price = 0
  crsr = find('$', text)
  while crsr do
    t = value(text[crsr+1..$])
    if t[1] = GET_SUCCESS then
      price += t[2]

3. Re: ex.exe hangs in a while loop

• Posted by Derek Parnell <ddparnell at bigpond.com> Jul 12, 2006
• 498 views

olddog wrote:
> 
> Oops! Punched a wrong button half way thorugh my post:
> 
> My 2.5 interpreter hangs (even the trace() debugger hangs) with this code:
> 
> }}}
<eucode>
> incude get.e
> procedure main()
>   integer crsr, price
>   sequence text, t
>   text = "/GRVY $.75 /GRVY $.75"
>   price = 0
>   crsr = find('$', text)
>   while crsr do
>     t = value(text[crsr+1..$])
>     if t[1] = GET_SUCCESS then
>       price += t[2]*100
>     end if
>     crsr = find('$', text[crsr+1..$])
>   end while
> end procedure
> </eucode>
{{{

> 
> If text only equals "/GRVY $.75" then it works fine, but as it is above
> it hangs (the debug trace locks up on the end while statement).
> 
> Workarounds, anyone?

I can see a problem. The second find() gives a result as an offset from the
first '$' and you don't adjust that to be an offset from the start of the text.
Try this instead...

    temp = find('$', text[crsr+1..$])
    if temp then
        crsr += temp+1
    end if
  end while

The details...
On the first find() it returns 7. So the second find() looks at the slice
starting at 8 which returns 10. This is the offset from the start of the slice,
not the start of the text. To adjust it you need to add the slice start position
to the returned value, making it 18.

-- 
Derek Parnell
Melbourne, Australia
Skype name: derek.j.parnell

5. Re: ex.exe hangs in a while loop

• Posted by Derek Parnell <ddparnell at bigpond.com> Jul 12, 2006
• 520 views

I meant to suggest that instead of using find() you use the find_from() function
below ...

global function find_from(object item, sequence source, integer start)
  integer pos
  if start > length(source) then
     return 0
  end if
  if start < 1 then
     return 0
  end if
  pos = find(item, source[start..$])
  if pos then
     pos += start - 1
  end if
  return pos

end function

Then you could code ...

   crsr = find_from('$', text, crsr+1)

-- 
Derek Parnell
Melbourne, Australia
Skype name: derek.j.parnell

7. Re: ex.exe hangs in a while loop

• Posted by Cuvier Christian <christian.cuvier at insee.fr> Jul 12, 2006
• 518 views

Subject: Re: ex.exe hangs in a while loop




Oops! Punched a wrong button half way thorugh my post:

My 2.5 interpreter hangs (even the trace() debugger hangs) with this code:

include get.e
procedure main()
  integer crsr, price
  sequence text, t
  text = "/GRVY $.75 /GRVY $.75"
  price = 0
  crsr = find('$', text)
  while crsr do
    t = value(text[crsr+1..$])
    if t[1] = GET_SUCCESS then
      price += t[2]*100
    end if
    crsr = find('$', text[crsr+1..$])
  end while
end procedure

If text only equals "/GRVY $.75" then it works fine, but as it is above
it hangs (the debug trace locks up on the end while statement).

Workarounds, anyone?

BTW, I am enjoying using this interpreter on an old DOS box!


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

This is not really a workaround, but setting the program logic right.

The line

crsr = find('$', text[crsr+1..$])

should read

text = text[crsr+1..$]
	crsr = find('$', text)

This works, as it changes the text so that the loop always appears to start
from scratch. The problem in the original code is that crsr is the position
of the next '$' relative to the previous, but you use it as an absolute
index into the unchanged 'text'.

And since you compute the tail of text twice, that's one time too many:

include get.e
procedure main()
  integer crsr, price
  sequence text, t
  text = "/GRVY $.75 /GRVY $.75"
  price = 0
  crsr = find('$', text)
  while crsr do
    text = text[crsr+1..$]
	t = value(text)
    if t[1] = GET_SUCCESS then
      price += t[2]*100
    end if
    crsr = find('$', text)
  end while
end procedure

Also, if you expect value() to fail sometimes, you probably have to add some
sort of reporting of such a condition, since price, which will be the sum of
all correctly read prices on return, may be inaccurate then. 

Oh, by the way, how do you retrieve the contents of that private variable?
You may need to turn the procedure into a function and add a "return price"
statement after the loop ends. Or to make price local rather than private.

HTH

CChris