list building

list building

[Brian S McQueen]

I am building a list of string via various calls to C functions.  When the
list of strings is complete I pass it off to the C based printing
function.  Anyway, I find myself building the list like this:

        (set! output-list (cons (sgids pref-login) output-list))
        (set! output-list (cons (gids) output-list))
        (set! output-list (cons (getd pref-login) output-list))

This seems very awkward.  How should I go about building a list a string
at a time?

Brian


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Re: list building

[Thien-Thi Nguyen]

   From: Brian S McQueen <bqueen@nas.nasa.gov>
   Date: Tue, 13 Jan 2004 16:11:23 -0800 (PST)

   [set! set! set!]

   This seems very awkward.

hey give your intution some credit.  it *IS* indeed very awkward!

   How should I go about building a list a
   string at a time?

generalize the problem: build a tree and then walk it (once) on
"output".  see html-data.scm and flatten.scm in this directory:

http://www.glug.org/people/ttn/software/
       ttn-pers-scheme/dist/0.32/ttn/    (split into two lines)

for example.  for an extremely elaborate example, look at LAML.

thi


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Re: list building

[Viktor Pavlenko]

>>>>> "TN" == Thien-Thi Nguyen <ttn@surf.glug.org> writes:

    TN>    [set! set! set!]

    TN>    This seems very awkward.

    TN> hey give your intution some credit.  it *IS* indeed very
    TN> awkward!

What about my question about define-syntax? Can you answer that?

Thanks

-- 
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Re: list building

[Marius Vollmer]

Thien-Thi Nguyen <ttn@surf.glug.org> writes:

>    From: Brian S McQueen <bqueen@nas.nasa.gov>
>    Date: Tue, 13 Jan 2004 16:11:23 -0800 (PST)
>
>    How should I go about building a list a
>    string at a time?
>
> generalize the problem: build a tree and then walk it (once) on
> "output".  see html-data.scm and flatten.scm in this directory:

Maybe he just wants to know about 'list' :-)

    (set! output-list (list (getd pref-login) (gids) (sgids pref-login)))

Or 'cons*':

    (set! output-list (cons* (getd pref-login) (gids) (sgids pref-login)
                             output-list))

Try

    guile> (help cons*)

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Re: list building

[Matt Hellige]

[Brian S McQueen <bqueen@nas.nasa.gov>]
> I am building a list of string via various calls to C functions.  When the
> list of strings is complete I pass it off to the C based printing
> function.  Anyway, I find myself building the list like this:
> 
>         (set! output-list (cons (sgids pref-login) output-list))
>         (set! output-list (cons (gids) output-list))
>         (set! output-list (cons (getd pref-login) output-list))
> 
> This seems very awkward.  How should I go about building a list a string
> at a time?
> 

Maybe you've oversimplified the problem in your example, but it seems
like you can just do:

  (define output-list
    (list 
      (sgids pref-login)
      (gids)
      (getd pref-login)))

If you already have an output-list you need to preserve, then:

  (set! output-list
    `(,(sgids pref-login)
      ,(gids)
      ,(getd pref-login)
      . ,output-list))

But again, my guess is there's some reason why this needs to be more
complicated...

Matt

-- 
Matt Hellige                  matt@immute.net
http://matt.immute.net


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Re: list building

[Stephen Compall]

Matt Hellige <matt@immute.net> writes:

> If you already have an output-list you need to preserve, then:
> 
>   (set! output-list
>     `(,(sgids pref-login)
>       ,(gids)
>       ,(getd pref-login)
>       . ,output-list))

Better,

(set! output-list (cons* (getd pref-login) (gids) (sgids pref-login)
                         output-list))

Particularly as the original pushed `sgids' first, IIRC. cons* is your
friend.

--
Stephen Compall or s11 or sirian

If you haven't enjoyed the material in the last few lectures then a career
in chartered accountancy beckons.
		-- Advice from the lecturer in the middle of the Stochastic
		   Systems course.

Panama undercover data haven Khaddafi Ft. Meade spy BLU-97 A/B [Hello
to all my friends and fans in domestic surveillance] Janet Reno BRLO
Perl-RSA World Trade Center UNSCOM NATO BCCI


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Re: list building

[Lynn Winebarger]

    Better to take TTN's advice if there's any portability desired.
Order of evaluation is not specified by the scheme standard.

Lynn

Stephen Compall wrote:
> Matt Hellige <matt@immute.net> writes:
> 
> 
>>If you already have an output-list you need to preserve, then:
>>
>>  (set! output-list
>>    `(,(sgids pref-login)
>>      ,(gids)
>>      ,(getd pref-login)
>>      . ,output-list))
> 
> 
> Better,
> 
> (set! output-list (cons* (getd pref-login) (gids) (sgids pref-login)
>                          output-list))
> 
> Particularly as the original pushed `sgids' first, IIRC. cons* is your
> friend.
> 



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Re: list building

[Brian S McQueen]

TTN's message seemed to go to a different list.  I never saw it.  What did
TTN say?

On Wed, 14 Jan 2004, Lynn Winebarger wrote:

>
>     Better to take TTN's advice if there's any portability desired.
> Order of evaluation is not specified by the scheme standard.
>
> Lynn
>
> Stephen Compall wrote:
> > Matt Hellige <matt@immute.net> writes:
> >
> >
> >>If you already have an output-list you need to preserve, then:
> >>
> >>  (set! output-list
> >>    `(,(sgids pref-login)
> >>      ,(gids)
> >>      ,(getd pref-login)
> >>      . ,output-list))
> >
> >
> > Better,
> >
> > (set! output-list (cons* (getd pref-login) (gids) (sgids pref-login)
> >                          output-list))
> >
> > Particularly as the original pushed `sgids' first, IIRC. cons* is your
> > friend.
> >
>
>
>
> _______________________________________________
> Guile-user mailing list
> Guile-user@gnu.org
> http://mail.gnu.org/mailman/listinfo/guile-user
>


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Re: list building

[Matt Hellige]

[Lynn Winebarger <owinebar@indiana.edu>]
> 
>     Better to take TTN's advice if there's any portability desired.
> Order of evaluation is not specified by the scheme standard.
> 

I think that's a bit of an overstatement. The other suggestions are
perfectly portable, and people write code like that all the time. It's
true that evaluation order is unspecified, but it often doesn't matter
(otherwise I think we'd see a lot more hand-crafted CPS in Scheme
programs).

In particular, it isn't at all clear to me whether it matters in this
case. Imperative code often over-specifies... However, you're right
that the issue certainly merits mention, and on that point I stand
corrected...

Matt

> 
> Stephen Compall wrote:
> > Matt Hellige <matt@immute.net> writes:
> > 
> > 
> >>If you already have an output-list you need to preserve, then:
> >>
> >>  (set! output-list
> >>    `(,(sgids pref-login)
> >>      ,(gids)
> >>      ,(getd pref-login)
> >>      . ,output-list))
> > 
> > 
> > Better,
> > 
> > (set! output-list (cons* (getd pref-login) (gids) (sgids pref-login)
> >                          output-list))
> > 
> > Particularly as the original pushed `sgids' first, IIRC. cons* is your
> > friend.
> > 
> 
> 
> 
> _______________________________________________
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> Guile-user@gnu.org
> http://mail.gnu.org/mailman/listinfo/guile-user

-- 
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http://matt.immute.net


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Re: list building

[Keith Wright]

> From: Brian S McQueen <bqueen@nas.nasa.gov>
> 
>         (set! output-list (cons (sgids pref-login) output-list))
>         (set! output-list (cons (gids) output-list))
>         (set! output-list (cons (getd pref-login) output-list))
> 
> This seems very awkward.  How should I go about building a list a string
> at a time?

Several people have already urged you not to build a string
at a time, but to make the whole list in one expression.
To answer your question though:
If you insist on adding one string at a time

 (define (add-to-output str)
   (set! output-list (cons str output-list)))
 (add-to-output (sgids pref-login))
 (add-to-output (gids))
 (add-to-output (getd pref-login))

-- 
     -- Keith Wright  <kwright@free-comp-shop.com>

Programmer in Chief, Free Computer Shop <http://www.free-comp-shop.com>
         ---  Food, Shelter, Source code.  ---


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Re: list building

[Brian S McQueen]

The cons* worked excellently.  When I used it a better structure became
clear.

BTW I do not seem to be getting all the message from this list.  Maybe it
is over aggressive spam filtering here at the office.

Brian

On Thu, 15 Jan 2004, Keith Wright wrote:

> > From: Brian S McQueen <bqueen@nas.nasa.gov>
> >
> >         (set! output-list (cons (sgids pref-login) output-list))
> >         (set! output-list (cons (gids) output-list))
> >         (set! output-list (cons (getd pref-login) output-list))
> >
> > This seems very awkward.  How should I go about building a list a string
> > at a time?
>
> Several people have already urged you not to build a string
> at a time, but to make the whole list in one expression.
> To answer your question though:
> If you insist on adding one string at a time
>
>  (define (add-to-output str)
>    (set! output-list (cons str output-list)))
>  (add-to-output (sgids pref-login))
>  (add-to-output (gids))
>  (add-to-output (getd pref-login))
>
> --
>      -- Keith Wright  <kwright@free-comp-shop.com>
>
> Programmer in Chief, Free Computer Shop <http://www.free-comp-shop.com>
>          ---  Food, Shelter, Source code.  ---
>
>
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> http://mail.gnu.org/mailman/listinfo/guile-user
>


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Re: list building

[Joshua Judson Rosen]

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On Wed, Jan 14, 2004 at 01:48:28PM -0500, Lynn Winebarger wrote:
> Stephen Compall wrote:
> >Matt Hellige <matt@immute.net> writes:
> >
> >(set! output-list (cons* (getd pref-login) (gids) (sgids pref-login)
> >                         output-list))
> >
> >Particularly as the original pushed `sgids' first, IIRC. cons* is your
> >friend.
>
>    Better to take TTN's advice if there's any portability desired.
> Order of evaluation is not specified by the scheme standard.

Why does that matter?

You're thinking that getd, gids, and/or sgids might have side-effects
that influence each other, I take it?

-- 
"Don't worry about people stealing your ideas.  If your ideas are any good,
 you'll have to ram them down people's throats." --Howard Aiken

[-- Attachment #1.2: Type: application/pgp-signature, Size: 189 bytes --]

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Re: list building

[Thien-Thi Nguyen]

   From: Viktor Pavlenko <vvp@rogers.com>
   Date: Tue, 13 Jan 2004 22:13:05 -0500

   What about my question about define-syntax? Can you answer that?

here's an answer but you may not be satisfied with it:

i played w/ the posted code briefly under guile 1.4.1.98 and was able to
make the error into other errors by (re)moving the last set of ellipses
to different places.

at the moment i'm starting to learn more about define-syntax by reading
dybvig's tspl d2 (online[1]) but that effort won't yield anything for
awhile...  when i get a better idea of what is going wrong, i'll try to
remember to post what i have discovered.

thi


________________________________________________
[1] http://www.scheme.com/tspl2d/index.html


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Re: list building

[Viktor Pavlenko]

>>>>> "TTN" == Thien-Thi Nguyen <ttn@surf.glug.org> writes:

    TTN>    From: Viktor Pavlenko <vvp@rogers.com>
    TTN>    Date: Tue, 13 Jan 2004 22:13:05 -0500

    TTN>    What about my question about define-syntax? Can you answer
    TTN>    that?

Sorry, that was not the best way of asking for help from my side...

    TTN> here's an answer but you may not be satisfied with it:

    TTN> i played w/ the posted code briefly under guile 1.4.1.98 and
    TTN> was able to make the error into other errors by (re)moving
    TTN> the last set of ellipses to different places.

    TTN> at the moment i'm starting to learn more about define-syntax
    TTN> by reading dybvig's tspl d2 (online[1]) but that effort won't
    TTN> yield anything for awhile...  when i get a better idea of
    TTN> what is going wrong, i'll try to remember to post what i have
    TTN> discovered.

I need to learn more about that. The tspl book is useful no matter how
many times one reads it :). I think the main problem with the code I
posted was introducing local bindings from within syntax-rules() and
expecting that `...' will be magically replaced with a following local
binding. Maybe syntax-case() is the way to go.

Being very excited with Scheme I wish I had studied CS instead of
chemistry when I was younger... What other texts would be useful to
read (without being bogged in math) to understand some more difficult
aspects of Scheme (macros, continuations) better?

Best regards

-- 
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Recommended Reading about Scheme

[Allister MacLeod]

On Sat, Jan 24, 2004 at 05:23:37PM -0500, Viktor Pavlenko wrote:
> Being very excited with Scheme I wish I had studied CS instead of
> chemistry when I was younger... What other texts would be useful to
> read (without being bogged in math) to understand some more difficult
> aspects of Scheme (macros, continuations) better?

I found _Structure and Interpretation of Computer Programs_ by
Sussman, Steele and Sussman to be very illuminating about Scheme, and
programming in general.  If you haven't read it, it would be well
worth checking it out from the library.

In the process of searching for bibliographical stuff, I found
http://library.readscheme.org/ which looks like it might have some
very good leads.

Hope these help,
 Allister

-- 
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 Elen síla lúmenn'omentielvo.


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errata on Recommended Reading for Scheme

[Allister MacLeod]

My apologies for the incorrect info in my earlier reply, but, the
authors of SICP are actually Abelson, Sussman and Sussman.  (I
probably pulled Guy L. Steele's name from my memory from R5RS or
something.)

Ciao,
 Allister

-- 
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 Elen síla lúmenn'omentielvo.


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Re: list building

[Thien-Thi Nguyen]

   From: Viktor Pavlenko <vvp@rogers.com>
   Date: Sat, 24 Jan 2004 17:23:37 -0500

   Being very excited with Scheme I wish I had studied CS instead of
   chemistry when I was younger...

it is probably better that you have exposure to something "real" (as
real as p orbitals can get, i suppose) before diving into the realm of
pure ego.  most computer scientists don't do science.  likewse most
computer engineers don't do engineering.  the distractions are many.

   What other texts would be useful to read (without being bogged in
   math) to understand some more difficult aspects of Scheme (macros,
   continuations) better?

all this depends on your learning process.  i suggest writing your own
howto docs by running an interpreter in an emacs buffer and periodically
saving the session to a file (add comments as necessary).  at the very
deepest levels of my todo stack is an emacs lisp tutorial composed in
this manner -- it was fun (and will be again once i get all this guile
related stuff popped).

thi


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