From: Christopher Dicely <cmdicely@...>
Date: 2009-03-11T23:38:31+09:00
Subject: Re: return doesn't always exit my method

On Wed, Mar 11, 2009 at 6:18 AM, Benjamin Thomas
<benjamin.thomas81@free.fr> wrote:
> Hi, I'm new to Ruby and programming in general.
> I'm coding a little script to train on multiplication tables but
> something's wrong:
>
> If I type 'exit', the function should normally exit, via a return
> statement. But this does not always happen and I really can't understand
> why. I've been scratching my head for a few hours on that so I'm posting
> here hoping somebody will be able to spot my obvious mistake!
>
> I'm trying to apply here the concept of recursion so maybe this is where
> I'm messing up.
>
> Thanks for your input,
> Ben

Your intuition on where the problem is is correct. Note that when
using recursion, each call to the function is a separate "layer", and
calling return only jumps you out of the current layer. So if you are
in the invocation of rand_multi() that you called from the top level,
return will exit rand_multi() back to the top level, but if you are in
an invocation of rand_multi() called from another invocation of
rand_multi, return will return you from the current invocation of
rand_multi() back to the calling invocation.

I hope that's clear enough. If not, you can get an illustration by
changing your rand_multi() method as follows:


def rand_multi(call_depth=0)  # <-- changed
 puts "entering rand_multi(#{call_depth})"  # <-- added
 num1 = rand(10)
 num2 = rand(10)
 got_wrong = false
 operation = "#{num1}*#{num2}"
 if $tested[operation].nil?
   puts "creation!"
   $tested[operation] = 0
 elsif $tested[operation] > 1
   puts "need restart"
   rand_multi(call_depth+1)       # <-- changed: forces function call again
   puts "returning to rand_multi(#{call_depth}"  # <-- added
 end
 puts "iteration #{$tested[operation]}"
 print operation, " = "
 before = Time.now
 time_before = (before.min * 60) + before.sec  # in case I go for a
coffee :)
 answer = gets.chomp
 if answer =~ /exit/
   puts "will exit now"
   return ##### <-- return statement does not always exit method; why??
######
   # exit
 elsif answer =~ /[0-9]+/
   answer = answer.to_i
 else
   puts "Please enter numbers only!"
   rand_multi()
 end
 if answer != num1 * num2
   print " [0;31m"                             # terminal colors
   puts "inside not equal"
   puts "No! Answer was '#{num1*num2}'"
   print " [0;m"
   sleep(1)
   # system "clear"
   got_wrong = true
   $tested[operation] -= 5         # give negative value
   rand_multi(call_depth+1)       # <-- changed
   puts "returning to rand_multi(#{call_depth}"  # <-- added
 elsif answer == num1 * num2
   after = Time.now
   time_after = (after.min * 60) + after.sec
   answer_time = time_after - time_before
   print " [1;34m"
   puts "inside equal"
   puts "Yes!, you answered in #{answer_time} seconds"
   print " [0;m"
   sleep(0.3)
   # system "clear"
   if got_wrong == false
     if answer_time < 3
       $tested[operation] += 1        # give positive value
     else
       $tested[operation] -= 1        # small penalty if answer too
slow
     end
   end
   rand_multi(call_depth+1)       # <-- changed
   puts "returning to rand_multi(#{call_depth}"  # <-- added
 end
end