Re: two elementary questions

[Alejandro Forero Cuervo]

    2. I've been doing the exercises in a learning-scheme book, and
    one is to implement the "list" function.  What is wrong here?
    
        (define (list . x)
                (cond
                        ((null? x) '())
                        ((null? (cdr x)) x)
                        (else (cons (car x) (ll (cdr x))))))

    (list 1 2 3 4) => (1 (2 3 4)), but I want (1 2 3 4).

I guess you mean "ll" where you said "list" in the code above.

Anyway.

You are defining your ll function to accept an unespecified number of
arguments as a list.  The following table attempts to explain what
ll'll (heh) see depending on the way you call it:

Call:             Value of x:
(ll 1 2 3 4)      (1 2 3 4)
(ll whatever)     (whatever)
(ll (2 3 4))      ((2 3 4))
(ll)              ()

In your first call, (ll 1 2 3 4), ll receives the list (1 2 3 4) as
its argument.  However, in your second (recursive) call, you are doing
(ll (2 3 4)) so it receives ((2 3 4)) rather than (2 3 4).

This is easy to fix but I guess telling you how to would spoil the fun
of the excersise. ;)

Good luck.

Alejo.
http://bachue.com/alejo

--
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      -- Albert Einstein.

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