I suppose you may be able to do some implementation specific things, that only work some of the time, using whatever introspection features your language provides you.

For instance you can check if a function is recursive (tail or regular) if it calls itself before it returns. Then, if it is recursive, you could maybe check the size of the stack on each call to determine if it’s tail recursive (stack wouldn’t grow linearly).

This seems rather hackish to me though, and I wouldn’t count on it working reliably. I’m sorry I don’t have more time to think about this problem. That’s just the first thing that popped into my head.

Maybe try posting your question on reddit.com/r/scheme

Oana

The prompt is not actually printed three times. I added that to make it more clear that it was output. Guess that didn’t work as well as I hoped. The actual output is:

(loop 2 (print "Hi"))
Hi
Hi
Hi
;===>#<unspecified>

(define-syntax set!
  (lambda (expr env)
    (let loop ((env env))
      (if (null? env)
       (error 'unbound-symbol "Unbound symbol:  " (car expr))
        (if (hash-table-exists? (current-environment env) (car expr))
            (hash-table-set! (current-environment env) (car expr) (lispy-eval (cadr expr) (current-environment env)))
            (loop (enclosing-environment env)))))

How is the prompt printed three times by the loop function, since loop does not directly call repl?

Thanks for taking the time to read this post and provide suggestions. I’ve made changes to both this page and my personal Chicken bookmarks. I appreciate the corrections very much! If you happen to see any other errors please drop me a note.

Nice summary.

Here are some corrections for some sites:

* chicken.wiki.br is not used anymore. Now we have wiki.call-cc.org. Basically all the “official” Chicken services are under the ca-cc.org domain. Chickadee is api.call-cc.org, wiki is wiki.call-cc.org, pasting is paste.call-cc.org, code is code.call-cc.org, bug tracking system is bugs.call-cc.org, the main page is http://www.call-cc.org. The egg index can be found at wiki.call-cc.org/egg-index

* The search service at callcc.org is seriously outdated. api.call-cc.org should be used instead.

Best wishes.
Mario

You get this error message:
[Errno 98] Address already in use

This server is meant as a very minimal testing server or as a starting point for someone interested in building their own server. I would contend that it is usually not a good idea to write your own server with the large number of capable open-source servers available.

As for the error above, I’ll reiterate the old doctor’s advice when you tell the doc, “It hurts when I do this.”

Then don’t do that.

I agree, for a public server, you would want a separate cgi directory. Which is why I made a note of that in the article. For a private testing server or project the old doctor’s advice works just fine.

Thanks again!

2.7 is not obsolete, there are many libraries you simply can’t use yet with 3.x. Yes, there will not be a 2.8, but 2.7 will be here for at least a couple of years and there is a tool to help port projects from 2.x to 3.x.

Python is a general purpose language. In other words, you can use it for just about anything you would use another language for. It is the perfect (IMHO) beginner language as it is simple to pick up, yet allows you “grow into it” and use it to produce large programs.

You will sometimes hear that Python is slow, I have never yet run across a situation where Python was a serious bottleneck. But if you do, Python has a simple interface to C, which you can use to write any speed critical code in (usually <1% of your code and I've never had to do this).

If Python is good enough for Peter Norvig, it's good enough for us. Not that you shouldn't learn other languages and use them where appropriate, but Python is a good solution to a lot of problems.

print in Python 3.x has changed to become a function instead of a statement. So you would use it like this…

print(“hello”, “world”)

Thanks for pointing that out, I’ll add a note in that mentions this. Right now I’m still using Python 2.7 as there are still a lot of major libraries that have not been ported to Python 3.x.

I’ll update this tutorial to 3.x when I start using it. Thanks again for the feedback!

>>> print “hello”, ‘world’
SyntaxError: invalid syntax
>>> print “hello”, ‘world’

I get above error. Please help. Am i using a wrong version of the lang??