# Wild ideas: Finding a missing 'end' **URL:** \ **Category:** Ruby\ **Created:** [July 29, 2006, 3:11am UTC](https://www.ruby-forum.com/t/wild-ideas-finding-a-missing-end/100463 "2006-07-29T03:11:01Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Mat\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ce7236/32.png) [@Mat\_S](https://www.ruby-forum.com/u/Mat_S)\ **Post date:** [July 29, 2006, 3:11am UTC](https://www.ruby-forum.com/t/wild-ideas-finding-a-missing-end/100463/1 "2006-07-29T03:11:01Z")
I was just reading a nuby question from the rails list and I had this thought: class MyClass def foo if true end end This code generates a parse error at the last line. Now most languages do this, so it’s not a big deal. But how frickin cool would it be if a future version of ruby looked at the indenting and made a guess as to where the missing end/} might be. Like: test.rb:5: parse error, unexpected $, expecting kEND. Did you miss an “end” on line 4? Maybe people have thought about this already. I’m just thinking out loud here, really. -Mat ---
**Author:** ![Mat\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ce7236/32.png) [@Mat\_S](https://www.ruby-forum.com/u/Mat_S)\ **Post date:** [July 29, 2006, 8:19am UTC](https://www.ruby-forum.com/t/wild-ideas-finding-a-missing-end/100463/2 "2006-07-29T08:19:26Z")
Yes, it has been considered. Unfortunately allowing the interpreter/compiler figure this out only works in the extremely simple case Consider: a=[1,2,3] for i in a begin if i \> 1 x = 3\*i end end puts x Obviously there is a missing end statement. However, where we put it makes a big difference. If we put it before the puts x, we get a very different output then if we put it after puts x. This is a simple example as well, even more complex examples will show that it gets very dangerous to let the interpreter figure out what you meant. Using indentation is dangerous, because indentation doesn’t mean anything in ruby normally, and trying to figure out the right thing would mean that we start having to be careful with indentation levels, and code works in strange ways because we don’t know ruby is ‘helping’ us out. It can make for very hard to find bugs. ---
**Author:** ![Mat\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ce7236/32.png) [@Mat\_S](https://www.ruby-forum.com/u/Mat_S)\ **Post date:** [July 29, 2006, 1:55pm UTC](https://www.ruby-forum.com/t/wild-ideas-finding-a-missing-end/100463/3 "2006-07-29T13:55:21Z")
Hi – On Sat, 29 Jul 2006, N Okia wrote: > x = 3\*i > Using indentation is dangerous, because indentation doesn’t mean > anything in ruby normally, and trying to figure out the right thing > would mean that we start having to be careful with indentation levels, > and code works in strange ways because we don’t know ruby is ‘helping’ > us out. It can make for very hard to find bugs. But surely just a warning can’t be harmful, even if it mentions what turns out to be the wrong line – ? David ---
**Author:** ![Mat\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ce7236/32.png) [@Mat\_S](https://www.ruby-forum.com/u/Mat_S)\ **Post date:** [July 29, 2006, 2:18pm UTC](https://www.ruby-forum.com/t/wild-ideas-finding-a-missing-end/100463/4 "2006-07-29T14:18:10Z")
unknown wrote: > Hi – > > On Sat, 29 Jul 2006, N Okia wrote: > > > x = 3\*i > > Using indentation is dangerous, because indentation doesn’t mean > > anything in ruby normally, and trying to figure out the right thing > > would mean that we start having to be careful with indentation levels, > > and code works in strange ways because we don’t know ruby is ‘helping’ > > us out. It can make for very hard to find bugs. > > But surely just a warning can’t be harmful, even if it mentions what > turns out to be the wrong line – ? > > David I agree as far as giving the coder the exact error line in a better way than currently, yes. That would help more than scanning the code for the missing end. 🙂 ---
**Author:** ![Mat\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ce7236/32.png) [@Mat\_S](https://www.ruby-forum.com/u/Mat_S)\ **Post date:** [July 29, 2006, 2:31pm UTC](https://www.ruby-forum.com/t/wild-ideas-finding-a-missing-end/100463/5 "2006-07-29T14:31:42Z")
> > Using indentation is dangerous, because indentation doesn’t mean > > anything in ruby normally, and trying to figure out the right thing > > would mean that we start having to be careful with indentation levels, > > and code works in strange ways because we don’t know ruby is ‘helping’ > > us out. It can make for very hard to find bugs. I think its better for it to guess than to just return the last line of the file each time. Perhaps return multiple guesses. Cheers Nic ---
**Author:** ![Mat\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ce7236/32.png) [@Mat\_S](https://www.ruby-forum.com/u/Mat_S)\ **Post date:** [July 29, 2006, 6:55pm UTC](https://www.ruby-forum.com/t/wild-ideas-finding-a-missing-end/100463/6 "2006-07-29T18:55:48Z")
Hi – On Sun, 30 Jul 2006, kate rhodes wrote: > You could go on and on and on and on with screwed up cases like this? Either > you write something complex enough to figure out what the hell us crazy > humans meant or you get misleading results which in my opinion is worse than > no results. > > Remember, a solution in the Ruby core has to work for all users not just the > users who happen to have good and consistent indentation habits. The solution could be to give a specific hint if it’s a simple case, and not if it isn’t 🙂 David ---
**Author:** ![Mat\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ce7236/32.png) [@Mat\_S](https://www.ruby-forum.com/u/Mat_S)\ **Post date:** [July 29, 2006, 6:49pm UTC](https://www.ruby-forum.com/t/wild-ideas-finding-a-missing-end/100463/7 "2006-07-29T18:49:26Z")
The problem with using indentation to even guess at an area in pretty much any language other than python is that it would require a huge amount of logic to account for the myriad possible edge cases. What happens when a user mixes tabs and spaces? If one line is indented 3 spaces and the next is 4 is that a typo or is it an intentional indication of a subsection? What happens when there’s a long method call that the developer has decided to indent a portion of on a second line instead of having the thing stretch way off to the right of the typical viewing area? You could go on and on and on and on with screwed up cases like this? Either you write something complex enough to figure out what the hell us crazy humans meant or you get misleading results which in my opinion is worse than no results. Remember, a solution in the Ruby core has to work for all users not just the users who happen to have good and consistent indentation habits. - kate = masukomi ---
**Author:** ![Mat\_S](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ce7236/32.png) [@Mat\_S](https://www.ruby-forum.com/u/Mat_S)\ **Post date:** [July 29, 2006, 7:48pm UTC](https://www.ruby-forum.com/t/wild-ideas-finding-a-missing-end/100463/8 "2006-07-29T19:48:58Z")
On 29/07/06, Mat S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > This code generates a parse error at the last line. Now most > languages do this, so it’s not a big deal. But how frickin cool > would it be if a future version of ruby looked at the indenting and > made a guess as to where the missing end/} might be. Like this? * * * def error\_line(code) File.open(‘tmp.rb’, ‘w’) do |io| io \<\< code end s = `ruby -c tmp.rb 2>&1` if (s =~ /parse error/) return s[/\d+/].to\_i else return false end end code = File.read(ARGV[0]) exit unless error\_line(code) lines = code.split(/\n/) x = lines.length / 2 xmin = 0 xmax = lines.length while l = error\_line(code) if l \< x xmax = x elsif l \> x xmin = x else break end x = xmin + (xmax - xmin)/2 code = (lines[0,x] + [‘end’] + lines[x…-1]).join(“\n”) end puts(“Error around line #{x+1}”) * * * This is pretty rough code that I just threw together without much thought, but it seems to work. Its temporary file handling leaves a lot to be desired. Paul.