From: Brian Candler <b.candler@...>
Date: 2008-11-03T22:34:38+09:00
Subject: Re: recursion and variable scope level

Adam Akhtar wrote:
> spaces in the end is set as false though it should be set to true. Is
> this soemthing to do with variable and parameter scope?

Yes. The 'spaces' inside the method definition is a completely separate 
variable to the 'spaces' you use outside, since 'def' starts a fresh 
scope.

One solution is to return both str and spaces from your function:

def reverse_string a_string, an_index, spaces
  spaces = true if a_string[an_index - 1].chr == ' '
  if an_index == 1
    return a_string[an_index - 1].chr, spaces
  else
    r1, r2 = reverse_string(a_string, an_index - 1, spaces)
    spaces ||= r2
    return a_string[an_index - 1].chr + r1, spaces
  end

end

#and i call it like this

str = "hello people"
rev, spaces = reverse_string str, str.length, spaces
puts rev
puts "Spaces present? #{spaces}"

Another option is to pass a lambda, which is a function which is called 
whenever a space is detected.

def reverse_string a_string, an_index, spaces
  spaces.call if a_string[an_index - 1].chr == ' '
  if an_index == 1
    return a_string[an_index - 1].chr
  else
    return a_string[an_index - 1].chr + reverse_string(a_string,
an_index - 1, spaces)
  end

end

#and i call it like this

spaces = false
str = "hello people"
puts reverse_string str, str.length, lambda { spaces=true }
puts "Spaces present? #{spaces}"
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