From: Park Heesob <phasis@...>
Date: 2002-06-07T10:53:44+09:00
Subject: Re: Unflatten

Hi,

"Niklas Frykholm" <r2d2@acc.umu.se> wrote in message
news:slrnafvnam.s4k.r2d2@shaka.acc.umu.se...
> [Shashank Date]:
> > I am trying to convert  a flat list (array) of  tokens  into a nested
list
> > (hence the name UNflatten) using a simple rule:
> > Every token which looks like  '(' begins a nested list and the
corresponding
> > ')' token ends it ... in a recursive fashion.
> > e.g:
> > ["a", "(","b", ")"]                 ==> ["a",[ "b" ]]
> > [ "(", "a", "(","b", ")", ")"]    ==> [["a",["b"]]]
>
> My suggestions:
>
> def unflatten(list, left='(', right=')')
>     current = []
>     stack = []
>
>     list.each do |x|
>         if x == left
>             stack << (current << [])
>             current = current[-1]
>         elsif x == right
>             raise "unbalanced" if stack.size == 0
>             current = stack.pop
>         else
>             current << x
>         end
>     end
>     raise "unbalanced" unless stack.size == 0
>     return current
> end
>

Simple but awful solution.

def unflatten(list)
  eval list.inspect.gsub(/"\(",/ , '[').gsub(/"\)"/ , ']')
end

Park Heesob.