[plt-scheme] guido on tail recursion

From: emre berat nebioğlu (beratn at gmail.com)
Date: Sat Apr 25 15:32:50 EDT 2009

this will be a newbie question.I read all mail but i wonder something.
can we say iteration instead of tail recursion.I dont know how to write a
program with iteration in scheme
in java there are for,do while but someone said you can make loop in scheme.
In tail recursive, program can be written by adding one extra parameter in
scheme,in java.But logic is same in both tail recursion and iteration "not
using stack (memory)". I mean using temprary value instead of using
memory.If i make a mistake i am sorry.I am beginner on programming.

And why are we writing recursive program.There are some advantages on that ?
Let say we wrote factorial function with recursion and call it like
factroail(50).Program stuck.If you use laptop,your machine warm up,may be
other process on machine cannot be proceed for sometime.

But you wrote this program with tail recursive.Your calculation ends with
two or three second.

So may be we prefer CPS.But both CPS and tail recursion is faster and
freeofcost and not diffucult for machine.But recursive is opposite.Why do we
still write program with recursive.

(your discussion is very advanced to me and i ask few question i try to
improve myself i hope you are welcommed me)

On Sat, Apr 25, 2009 at 9:49 PM, Joe Marshall <jmarshall at alum.mit.edu>wrote:

> The word `call' itself is problematic because it implies a return.
> On Sat, Apr 25, 2009 at 11:42 AM, Shriram Krishnamurthi <sk at cs.brown.edu>
> wrote:
> > It is dangerous to use the term "tail recursion" ever, unless you
> > really, really mean recursion in the very narrow sense by which the
> > doofus-in-the-street understands it, namely "a function that
> > *directly* calls itself".
> >
> > I have seen an especially strong trend amongst MIT folks to use "tail
> > recursion" to refer to the general case of "a sequence of calls that
> > eventually result back in the same function, even if indirectly".
> > This is technically correct, and the meaning of this general phrase
> > may be obvious to all members of the very highly intelligent species
> > that populates MIT.  But it confuses the doofus, and that's a problem,
> > because it leads to the sort of confusion in Guido's message and
> > ensuing discussion -- on a topic that needs less, not more, confusion.
> >
> > [Tail calls that do not lead to recursion are still worth optimizing,
> > but they cannot lead to order-of-complexity increases in size except
> > in pathological cases, so they are not as interesting to focus on
> > because that, too, distracts the conversation.]
> >
> > Shriram
> >
> --
> ~jrm
> _________________________________________________
>  For list-related administrative tasks:
>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
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