# Problem with recursion? (was [plt-scheme] Re: Novice needs help writing function )

 From: Matthias Felleisen (matthias at ccs.neu.edu) Date: Fri Jan 4 15:28:28 EST 2008 Previous message: Problem with recursion? (was [plt-scheme] Re: Novice needs help writing function ) Next message: Problem with recursion? (was [plt-scheme] Re: Novice needs help writing function ) Messages sorted by: [date] [thread] [subject] [author]

```On Jan 4, 2008, at 1:41 PM, Yavuz Arkun wrote:

> The number of explicit variables in the recursive version is
> deceptive. When I am trying to understand a program, I put myself
> in the place of the computer and work through the program in my
> mind. For the iterative version, everything I need to remember are
> explicitly named. For recursive algorithms, I need to keep track of
> the implicit variables as well, such as how deep I am into the
> recursion, and what the intermediate values are, because I will
> need them on my way back.
>
> Personally, I can manage 1 or 2 levels mentally, and if I use pen
> and paper maybe a few more. After that, I need to take a leap of
> faith, and inductively conclude that if it works for the simplest
> case, and for the one after that, it should work for all cases.
>
> In other words, neither the conciseness of the program text, nor
> the elegance of the expressed ideas necessarily means "easy to
> understand", unless you are prepared to take the leap.
>
> I can do that, because I know recursion works as a general concept.
> It may be more difficult if you are new to the idea. Even more so,
> when you realize that the 'elegant' method can have rather
> inelegant space and/or time characteristics. Then you start to feel
> like you must be missing something and become frustrated.
>
> Therefore, recursion (like any other method) should be illustrated
> using examples that can be best solved with recursion.

Please do take a look at HtDP. Your message suggests that you were
trained by or as an EE :-)

-- Matthias

```

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