From: Christian Soltenborn
Subject: Hint for "EVAL: variable pos has no value"
Date: 
Message-ID: <c0eum5$16o0sj$1@ID-36219.news.uni-berlin.de>
Hi again,

the following function

(defun left (state)
	(let ((pos (element-index state '0))))
	(cond
		((equal '0 pos) nil)
		((equal '3 pos) nil)
		((equal '6 pos) nil)
		(t swap state (- pos 1) pos)
	)
)

produces the error message mentioned in the subject.

The function element-index itself works fine.

Can anyone give me a hint?

Thanks a lot,
Christian

P.S. Every other comment is highly appreciated, too. I'm just giving 
myself a Lisp crash course...
From: Artie Gold
Subject: Re: Hint for "EVAL: variable pos has no value"
Date: 
Message-ID: <c0evf4$15r7uo$1@ID-219787.news.uni-berlin.de>
Christian Soltenborn wrote:
> Hi again,
> 
> the following function
> 
> (defun left (state)
>     (let ((pos (element-index state '0)))) ;; extra paren?
>     (cond
>         ((equal '0 pos) nil)
>         ((equal '3 pos) nil)
>         ((equal '6 pos) nil)
>         (t swap state (- pos 1) pos) ;; this line looks funky
>     )
> )
> 
> produces the error message mentioned in the subject.
> 
> The function element-index itself works fine.
> 
> Can anyone give me a hint?
> 
> Thanks a lot,
> Christian
> 
> P.S. Every other comment is highly appreciated, too. I'm just giving 
> myself a Lisp crash course...

Your parentheses are off.

Suggestion: if you don't already have one, get an editor that is (or can 
be made to be) Lisp-aware.

[Hint: the bindings in a `let' form only exist within the `let' form.]
[Hint 2: As, by your indentation style, you're from the C* world, your 
problem is roughly analogous to (we'll assume C++ for the moment):
    for (int i = 0; i < n; i++);
    {
       // whatever code goes here, involving `i'
    }]

HTH,
--ag

-- 
Artie Gold -- Austin, Texas

"Yeah. It's an urban legend. But it's a *great* urban legend!"
From: jan
Subject: Re: Hint for "EVAL: variable pos has no value"
Date: 
Message-ID: <ud68iraid.fsf@iprimus.com.au>
Artie Gold <·········@austin.rr.com> writes:

> [Hint 2: As, by your indentation style, you're from the C* world, your
> problem is roughly analogous to (we'll assume C++ for the moment):
>     for (int i = 0; i < n; i++);

For the record, this code is valid in C99.

gcc -std=gnu99

-- 
jan
From: Artie Gold
Subject: Re: Hint for "EVAL: variable pos has no value"
Date: 
Message-ID: <c0hjof$17h7fu$1@ID-219787.news.uni-berlin.de>
jan wrote:
> Artie Gold <·········@austin.rr.com> writes:
> 
> 
>>[Hint 2: As, by your indentation style, you're from the C* world, your
>>problem is roughly analogous to (we'll assume C++ for the moment):
>>    for (int i = 0; i < n; i++);
> 
> 
> For the record, this code is valid in C99.

...and, of course, equally useless!! ;-)
> 
> gcc -std=gnu99
> 
Cheers,
--ag

-- 
Artie Gold -- Austin, Texas

"Yeah. It's an urban legend. But it's a *great* urban legend!"
From: Joe Marshall
Subject: Re: Hint for "EVAL: variable pos has no value"
Date: 
Message-ID: <y8r86hdi.fsf@comcast.net>
Christian Soltenborn <···················@webmail.de> writes:

> Hi again,
>
> the following function
>
> (defun left (state)
> 	(let ((pos (element-index state '0))))
> 	(cond
> 		((equal '0 pos) nil)
> 		((equal '3 pos) nil)
> 		((equal '6 pos) nil)
> 		(t swap state (- pos 1) pos)
> 	)
> )
>
> produces the error message mentioned in the subject.
>
> The function element-index itself works fine.
>
> Can anyone give me a hint?

Scope.  The COND isn't `in' the LET.

Compare it to this:

> (defun left (state)
>   (let ((pos (element-index state 0)))
>     (cond ((= pos 0) nil)
>           ((= pos 3) nil)
>           ((= pos 6) nil)
>           (t (swap state (- pos 1) pos)))))


-- 
~jrm
comp.lang.lisp / 2004 / feb