[30495] in Perl-Users-Digest
Perl-Users Digest, Issue: 1738 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Tue Jul 22 09:09:43 2008
Date: Tue, 22 Jul 2008 06:09:06 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Tue, 22 Jul 2008 Volume: 11 Number: 1738
Today's topics:
Re: Mail::IMAPClient usage... <yogeshkagrawal@gmail.com>
Re: Mail::IMAPClient usage... <yogeshkagrawal@gmail.com>
Re: Mail::IMAPClient usage... <rfs9999@earthlink.net>
Posting Guidelines for comp.lang.perl.misc ($Revision: tadmc@seesig.invalid
Re: proliferation of computer languages <jurgenex@hotmail.com>
Re: The Importance of Terminology's Quality <martin@see_sig_for_address.invalid>
Re: The Importance of Terminology's Quality <josef.moellers@fujitsu-siemens.com>
Re: The Importance of Terminology's Quality (Rob Warnock)
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Tue, 22 Jul 2008 01:04:30 -0700 (PDT)
From: Yogi <yogeshkagrawal@gmail.com>
Subject: Re: Mail::IMAPClient usage...
Message-Id: <57245d5b-d14b-4361-8590-7e4769b8ab31@x35g2000hsb.googlegroups.com>
On Jul 22, 11:41=A0am, Martijn Lievaart <m...@rtij.nl.invlalid> wrote:
> On Mon, 21 Jul 2008 21:47:41 -0700, Yogi wrote:
> > Hi All,
> > I am trying to login to my gmail id using MAIL::IMAPClient modules
> > available in CPAN. =A0I took sample code available (for my POC) but it =
is
> > not working. Here is the snippet for your reference:
>
> > use strict;
> > use warnings;
> > # Use CPAN modules to handle mails
> > use Mail::IMAPClient;
>
> > my ($MAILSERVER,$USER,$PW,$num) =3D ();
>
> > ($MAILSERVER,$USER,$PW,$num) =3D ('pop.gmail.com:995/pop3/ssl',
> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 'm...@g=
mail.com',
> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 'mypwd'=
);
>
> Ahum, IMAP is not pop3, and Mail::IMAPClient does only IMAP. I think you
> should look for a pop3 client library.
>
> M4
Thanks Martijn. As you suggested, Mail::POP3Client is available which
I might use. So, in run time if I have to go to IMAP, i will have to
use IMAPClient otherwise POP3Client :(.
Will try using POP3 library for now.
Regards,
Y
------------------------------
Date: Tue, 22 Jul 2008 02:29:50 -0700 (PDT)
From: Yogi <yogeshkagrawal@gmail.com>
Subject: Re: Mail::IMAPClient usage...
Message-Id: <5aa1a4fb-c511-4f6a-aa58-e4e2f9561e49@y21g2000hsf.googlegroups.com>
On Jul 22, 1:04=A0pm, Yogi <yogeshkagra...@gmail.com> wrote:
> On Jul 22, 11:41=A0am, Martijn Lievaart <m...@rtij.nl.invlalid> wrote:
>
>
>
> > On Mon, 21 Jul 2008 21:47:41 -0700, Yogi wrote:
> > > Hi All,
> > > I am trying to login to my gmail id using MAIL::IMAPClient modules
> > > available in CPAN. =A0I took sample code available (for my POC) but i=
t is
> > > not working. Here is the snippet for your reference:
>
> > > use strict;
> > > use warnings;
> > > # Use CPAN modules to handle mails
> > > use Mail::IMAPClient;
>
> > > my ($MAILSERVER,$USER,$PW,$num) =3D ();
>
> > > ($MAILSERVER,$USER,$PW,$num) =3D ('pop.gmail.com:995/pop3/ssl',
> > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 'm...=
@gmail.com',
> > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 'mypw=
d');
>
> > Ahum, IMAP is not pop3, and Mail::IMAPClient does only IMAP. I think yo=
u
> > should look for a pop3 client library.
>
> > M4
>
> Thanks Martijn. =A0As you suggested, Mail::POP3Client is available which
> I might use. So, in run time if I have to go to IMAP, i will have to
> use IMAPClient otherwise POP3Client :(.
> Will try using POP3 library for now.
>
> Regards,
> Y
Well, I tried using POP3Client as well but no success.
use strict;
use Mail::POP3Client;
my $pop =3D new Mail::POP3Client( USER =3D> 'myid',
PASSWORD =3D> 'mypwd',
HOST =3D> "pop.gmail.com:995/pop3/
ssl",
USESSL =3D> 1,
PORT =3D> 995,
DEBUG =3D> 1
) || die("Error here $@");
my $msgCount =3D $pop->Count();
print "msgCount =3D $msgCount \n";
for( my $i =3D 1; $i <=3D $pop->Count(); $i++ ) {
foreach( $pop->Head( $i ) ) {
/^(From|Subject):\s+/i && print $_, "\n";
}
}
$pop->Close();
this code is not failing while trying to connect but giving msgCount =3D
-1. Am I missing anything here again?
Regards,
------------------------------
Date: Tue, 22 Jul 2008 08:05:22 -0500
From: Rick Sanders <rfs9999@earthlink.net>
Subject: Re: Mail::IMAPClient usage...
Message-Id: <40111$4885db12$12405@news.teranews.com>
> Well, I tried using POP3Client as well but no success.
> use strict;
> use Mail::POP3Client;
> my $pop = new Mail::POP3Client( USER => 'myid',
> PASSWORD => 'mypwd',
> HOST => "pop.gmail.com:995/pop3/
> ssl",
> USESSL => 1,
> PORT => 995,
> DEBUG => 1
> ) || die("Error here $@");
Your host argument is incorrect so you're not actually getting a
connection to the gmail POP server. Use the following instead:
HOST => "pop.gmail.com:995",
It's not necessary to supply the port number either.
-Rick
** Posted from http://www.teranews.com **
------------------------------
Date: Tue, 22 Jul 2008 07:11:12 GMT
From: tadmc@seesig.invalid
Subject: Posting Guidelines for comp.lang.perl.misc ($Revision: 1.8 $)
Message-Id: <kKfhk.33638$ZE5.13089@nlpi061.nbdc.sbc.com>
Outline
Before posting to comp.lang.perl.misc
Must
- Check the Perl Frequently Asked Questions (FAQ)
- Check the other standard Perl docs (*.pod)
Really Really Should
- Lurk for a while before posting
- Search a Usenet archive
If You Like
- Check Other Resources
Posting to comp.lang.perl.misc
Is there a better place to ask your question?
- Question should be about Perl, not about the application area
How to participate (post) in the clpmisc community
- Carefully choose the contents of your Subject header
- Use an effective followup style
- Speak Perl rather than English, when possible
- Ask perl to help you
- Do not re-type Perl code
- Provide enough information
- Do not provide too much information
- Do not post binaries, HTML, or MIME
Social faux pas to avoid
- Asking a Frequently Asked Question
- Asking a question easily answered by a cursory doc search
- Asking for emailed answers
- Beware of saying "doesn't work"
- Sending a "stealth" Cc copy
Be extra cautious when you get upset
- Count to ten before composing a followup when you are upset
- Count to ten after composing and before posting when you are upset
-----------------------------------------------------------------
Posting Guidelines for comp.lang.perl.misc ($Revision: 1.8 $)
This newsgroup, commonly called clpmisc, is a technical newsgroup
intended to be used for discussion of Perl related issues (except job
postings), whether it be comments or questions.
As you would expect, clpmisc discussions are usually very technical in
nature and there are conventions for conduct in technical newsgroups
going somewhat beyond those in non-technical newsgroups.
The article at:
http://www.catb.org/~esr/faqs/smart-questions.html
describes how to get answers from technical people in general.
This article describes things that you should, and should not, do to
increase your chances of getting an answer to your Perl question. It is
available in POD, HTML and plain text formats at:
http://www.rehabitation.com/clpmisc.shtml
For more information about netiquette in general, see the "Netiquette
Guidelines" at:
http://andrew2.andrew.cmu.edu/rfc/rfc1855.html
A note to newsgroup "regulars":
Do not use these guidelines as a "license to flame" or other
meanness. It is possible that a poster is unaware of things
discussed here. Give them the benefit of the doubt, and just
help them learn how to post, rather than assume that they do
know and are being the "bad kind" of Lazy.
A note about technical terms used here:
In this document, we use words like "must" and "should" as
they're used in technical conversation (such as you will
encounter in this newsgroup). When we say that you *must* do
something, we mean that if you don't do that something, then
it's unlikely that you will benefit much from this group.
We're not bossing you around; we're making the point without
lots of words.
Do *NOT* send email to the maintainer of these guidelines. It will be
discarded unread. The guidelines belong to the newsgroup so all
discussion should appear in the newsgroup. I am just the secretary that
writes down the consensus of the group.
Before posting to comp.lang.perl.misc
Must
This section describes things that you *must* do before posting to
clpmisc, in order to maximize your chances of getting meaningful replies
to your inquiry and to avoid getting flamed for being lazy and trying to
have others do your work.
The perl distribution includes documentation that is copied to your hard
drive when you install perl. Also installed is a program for looking
things up in that (and other) documentation named 'perldoc'.
You should either find out where the docs got installed on your system,
or use perldoc to find them for you. Type "perldoc perldoc" to learn how
to use perldoc itself. Type "perldoc perl" to start reading Perl's
standard documentation.
Check the Perl Frequently Asked Questions (FAQ)
Checking the FAQ before posting is required in Big 8 newsgroups in
general, there is nothing clpmisc-specific about this requirement.
You are expected to do this in nearly all newsgroups.
You can use the "-q" switch with perldoc to do a word search of the
questions in the Perl FAQs.
Check the other standard Perl docs (*.pod)
The perl distribution comes with much more documentation than is
available for most other newsgroups, so in clpmisc you should also
see if you can find an answer in the other (non-FAQ) standard docs
before posting.
It is *not* required, or even expected, that you actually *read* all of
Perl's standard docs, only that you spend a few minutes searching them
before posting.
Try doing a word-search in the standard docs for some words/phrases
taken from your problem statement or from your very carefully worded
"Subject:" header.
Really Really Should
This section describes things that you *really should* do before posting
to clpmisc.
Lurk for a while before posting
This is very important and expected in all newsgroups. Lurking means
to monitor a newsgroup for a period to become familiar with local
customs. Each newsgroup has specific customs and rituals. Knowing
these before you participate will help avoid embarrassing social
situations. Consider yourself to be a foreigner at first!
Search a Usenet archive
There are tens of thousands of Perl programmers. It is very likely
that your question has already been asked (and answered). See if you
can find where it has already been answered.
One such searchable archive is:
http://groups.google.com/advanced_group_search
If You Like
This section describes things that you *can* do before posting to
clpmisc.
Check Other Resources
You may want to check in books or on web sites to see if you can
find the answer to your question.
But you need to consider the source of such information: there are a
lot of very poor Perl books and web sites, and several good ones
too, of course.
Posting to comp.lang.perl.misc
There can be 200 messages in clpmisc in a single day. Nobody is going to
read every article. They must decide somehow which articles they are
going to read, and which they will skip.
Your post is in competition with 199 other posts. You need to "win"
before a person who can help you will even read your question.
These sections describe how you can help keep your article from being
one of the "skipped" ones.
Is there a better place to ask your question?
Question should be about Perl, not about the application area
It can be difficult to separate out where your problem really is,
but you should make a conscious effort to post to the most
applicable newsgroup. That is, after all, where you are the most
likely to find the people who know how to answer your question.
Being able to "partition" a problem is an essential skill for
effectively troubleshooting programming problems. If you don't get
that right, you end up looking for answers in the wrong places.
It should be understood that you may not know that the root of your
problem is not Perl-related (the two most frequent ones are CGI and
Operating System related), so off-topic postings will happen from
time to time. Be gracious when someone helps you find a better place
to ask your question by pointing you to a more applicable newsgroup.
How to participate (post) in the clpmisc community
Carefully choose the contents of your Subject header
You have 40 precious characters of Subject to win out and be one of
the posts that gets read. Don't waste them. Take care while
composing them, they are the key that opens the door to getting an
answer.
Spend them indicating what aspect of Perl others will find if they
should decide to read your article.
Do not spend them indicating "experience level" (guru, newbie...).
Do not spend them pleading (please read, urgent, help!...).
Do not spend them on non-Subjects (Perl question, one-word
Subject...)
For more information on choosing a Subject see "Choosing Good
Subject Lines":
http://www.cpan.org/authors/id/D/DM/DMR/subjects.post
Part of the beauty of newsgroup dynamics, is that you can contribute
to the community with your very first post! If your choice of
Subject leads a fellow Perler to find the thread you are starting,
then even asking a question helps us all.
Use an effective followup style
When composing a followup, quote only enough text to establish the
context for the comments that you will add. Always indicate who
wrote the quoted material. Never quote an entire article. Never
quote a .signature (unless that is what you are commenting on).
Intersperse your comments *following* each section of quoted text to
which they relate. Unappreciated followup styles are referred to as
"top-posting", "Jeopardy" (because the answer comes before the
question), or "TOFU" (Text Over, Fullquote Under).
Reversing the chronology of the dialog makes it much harder to
understand (some folks won't even read it if written in that style).
For more information on quoting style, see:
http://web.presby.edu/~nnqadmin/nnq/nquote.html
Speak Perl rather than English, when possible
Perl is much more precise than natural language. Saying it in Perl
instead will avoid misunderstanding your question or problem.
Do not say: I have variable with "foo\tbar" in it.
Instead say: I have $var = "foo\tbar", or I have $var = 'foo\tbar',
or I have $var = <DATA> (and show the data line).
Ask perl to help you
You can ask perl itself to help you find common programming mistakes
by doing two things: enable warnings (perldoc warnings) and enable
"strict"ures (perldoc strict).
You should not bother the hundreds/thousands of readers of the
newsgroup without first seeing if a machine can help you find your
problem. It is demeaning to be asked to do the work of a machine. It
will annoy the readers of your article.
You can look up any of the messages that perl might issue to find
out what the message means and how to resolve the potential mistake
(perldoc perldiag). If you would like perl to look them up for you,
you can put "use diagnostics;" near the top of your program.
Do not re-type Perl code
Use copy/paste or your editor's "import" function rather than
attempting to type in your code. If you make a typo you will get
followups about your typos instead of about the question you are
trying to get answered.
Provide enough information
If you do the things in this item, you will have an Extremely Good
chance of getting people to try and help you with your problem!
These features are a really big bonus toward your question winning
out over all of the other posts that you are competing with.
First make a short (less than 20-30 lines) and *complete* program
that illustrates the problem you are having. People should be able
to run your program by copy/pasting the code from your article. (You
will find that doing this step very often reveals your problem
directly. Leading to an answer much more quickly and reliably than
posting to Usenet.)
Describe *precisely* the input to your program. Also provide example
input data for your program. If you need to show file input, use the
__DATA__ token (perldata.pod) to provide the file contents inside of
your Perl program.
Show the output (including the verbatim text of any messages) of
your program.
Describe how you want the output to be different from what you are
getting.
If you have no idea at all of how to code up your situation, be sure
to at least describe the 2 things that you *do* know: input and
desired output.
Do not provide too much information
Do not just post your entire program for debugging. Most especially
do not post someone *else's* entire program.
Do not post binaries, HTML, or MIME
clpmisc is a text only newsgroup. If you have images or binaries
that explain your question, put them in a publically accessible
place (like a Web server) and provide a pointer to that location. If
you include code, cut and paste it directly in the message body.
Don't attach anything to the message. Don't post vcards or HTML.
Many people (and even some Usenet servers) will automatically filter
out such messages. Many people will not be able to easily read your
post. Plain text is something everyone can read.
Social faux pas to avoid
The first two below are symptoms of lots of FAQ asking here in clpmisc.
It happens so often that folks will assume that it is happening yet
again. If you have looked but not found, or found but didn't understand
the docs, say so in your article.
Asking a Frequently Asked Question
It should be understood that you may have missed the applicable FAQ
when you checked, which is not a big deal. But if the Frequently
Asked Question is worded similar to your question, folks will assume
that you did not look at all. Don't become indignant at pointers to
the FAQ, particularly if it solves your problem.
Asking a question easily answered by a cursory doc search
If folks think you have not even tried the obvious step of reading
the docs applicable to your problem, they are likely to become
annoyed.
If you are flamed for not checking when you *did* check, then just
shrug it off (and take the answer that you got).
Asking for emailed answers
Emailed answers benefit one person. Posted answers benefit the
entire community. If folks can take the time to answer your
question, then you can take the time to go get the answer in the
same place where you asked the question.
It is OK to ask for a *copy* of the answer to be emailed, but many
will ignore such requests anyway. If you munge your address, you
should never expect (or ask) to get email in response to a Usenet
post.
Ask the question here, get the answer here (maybe).
Beware of saying "doesn't work"
This is a "red flag" phrase. If you find yourself writing that,
pause and see if you can't describe what is not working without
saying "doesn't work". That is, describe how it is not what you
want.
Sending a "stealth" Cc copy
A "stealth Cc" is when you both email and post a reply without
indicating *in the body* that you are doing so.
Be extra cautious when you get upset
Count to ten before composing a followup when you are upset
This is recommended in all Usenet newsgroups. Here in clpmisc, most
flaming sub-threads are not about any feature of Perl at all! They
are most often for what was seen as a breach of netiquette. If you
have lurked for a bit, then you will know what is expected and won't
make such posts in the first place.
But if you get upset, wait a while before writing your followup. I
recommend waiting at least 30 minutes.
Count to ten after composing and before posting when you are upset
After you have written your followup, wait *another* 30 minutes
before committing yourself by posting it. You cannot take it back
once it has been said.
AUTHOR
Tad McClellan and many others on the comp.lang.perl.misc newsgroup.
--
Tad McClellan
email: perl -le "print scalar reverse qq/moc.noitatibaher\100cmdat/"
------------------------------
Date: Tue, 22 Jul 2008 10:38:07 GMT
From: Jürgen Exner <jurgenex@hotmail.com>
Subject: Re: proliferation of computer languages
Message-Id: <ltdb84trgran3aqvv7qhf4s1ths4v9gjvl@4ax.com>
Chris Rathman <Chris.Rathman@gmail.com> wrote:
>I can't say that I see any particular point to the essay.
You must be new here. There never is any particular point to Xah Lee's
rantings except to cross-post borderline topics to borderline relevant
NGs and then lay back and enjoy the ensuing slaughter.
PLEASE DO NOT FEED THE TROLL
>On Jul 18, 12:17 pm, "xah...@gmail.com" <xah...@gmail.com> wrote:
jue
------------------------------
Date: Tue, 22 Jul 2008 10:21:50 +0100
From: Martin Gregorie <martin@see_sig_for_address.invalid>
Subject: Re: The Importance of Terminology's Quality
Message-Id: <pan.2008.07.22.09.21.32.805990@see_sig_for_address.invalid>
On Tue, 24 Jun 2008 18:42:15 -0400, John W Kennedy wrote:
> David Combs wrote:
>> passing
>> *unnamed* functions as args (could Algol 60 also do something like that,
>> via something it maybe termed a "thunk")
>
> No, the "thunks" were necessary at the machine-language level to
> /implement/ ALGOL 60, but they could not be expressed /in/ ALGOL.
>
Are you sure about that?
The first time I ran across the term "thunking" was when Windows 3
introduced the Win32S shim and hence the need to switch addressing between
16 bit and 32 bit modes across call interfaces. That was called "thunking"
by Microsoft and even they would surely admit it was a kludge.
I used Algol 60 on an Elliott 503 and the ICL 1900 series back when it was
a current language. The term "thunking" did not appear in either compiler
manual nor in any Algol 60 language definition I've seen. A60 could pass
values by name or value and procedures by name. That was it. Call by name
is what is now referred to as reference passing.
I should also point out that Algol 60 was initially written as a means for
communicating algorithms between people. Compiler implementations came
later. In consequence the language did not define links to libraries or
i/o methods. Both features were compiler specific - for instance the
Elliott introduced 'input' and 'print' reserved words and syntax while the
1900 compilers used function calls. The Elliott approach was more readable.
Algol 60 did not have 'functions'. It had procedures which could be
declared to return values or not. A procedure that returned a value was
equivalent to a function but the term 'function' was not used. Similarly
it did not have a mechanism for declaring anonymous procedures. That, like
the incorporation of machine code inserts, would have been a
compiler-specific extension, so it is a terminological mistake to refer to
it without specifying the implementing compiler.
--
martin@ | Martin Gregorie
gregorie. |
org | Zappa fan & glider pilot
------------------------------
Date: Tue, 22 Jul 2008 11:56:41 +0200
From: Josef Moellers <josef.moellers@fujitsu-siemens.com>
Subject: Re: The Importance of Terminology's Quality
Message-Id: <g64arv$aab$1@nntp.fujitsu-siemens.com>
Martin Gregorie wrote:
> Are you sure about that?
> I used Algol 60 on an Elliott 503 and the ICL 1900 series back when it was
> a current language. The term "thunking" did not appear in either compiler
> manual nor in any Algol 60 language definition I've seen. A60 could pass
> values by name or value and procedures by name. That was it. Call by name
> is what is now referred to as reference passing.
Are you sure about that? ;-)
AFAIK "Call by name" is *not* the same as passing an argument by
reference. With "call by name" you can implement this wonderful thing
called "Jensen's Device", which you cannot do when you pass parameters
by reference!
Josef
--
These are my personal views and not those of Fujitsu Siemens Computers!
Josef Möllers (Pinguinpfleger bei FSC)
If failure had no penalty success would not be a prize (T. Pratchett)
Company Details: http://www.fujitsu-siemens.com/imprint.html
------------------------------
Date: Tue, 22 Jul 2008 07:23:22 -0500
From: rpw3@rpw3.org (Rob Warnock)
Subject: Re: The Importance of Terminology's Quality
Message-Id: <Dq-dnZYE9JanTBjVnZ2dnUVZ_jadnZ2d@speakeasy.net>
Martin Gregorie <martin@see_sig_for_address.invalid> wrote:
+---------------
| John W Kennedy wrote:
| > No, the "thunks" were necessary at the machine-language level to
| > /implement/ ALGOL 60, but they could not be expressed /in/ ALGOL.
|
| Are you sure about that?
+---------------
I don't know if John is, but *I* am! ;-}
+---------------
| I used Algol 60 on an Elliott 503 and the ICL 1900 series back when
| it was a current language. The term "thunking" did not appear in either
| compiler manual nor in any Algol 60 language definition I've seen.
+---------------
It wouldn't have been. Thunks were something used by Algol 60
*compiler writers* in the code generated by their compilers to
implement the semantics of Algol 60 call-by-name, but were not
visible to users at all [except that they allowed call-by-name
to "work right"].
+---------------
| A60 could pass values by name or value and procedures by name. That
| was it. Call by name is what is now referred to as reference passing.
+---------------
(*sigh*) NO, IT IS NOT!!! Please go read the following:
http://en.wikipedia.org/wiki/Thunk
http://en.wikipedia.org/wiki/Evaluation_strategy#Call_by_name
http://en.wikipedia.org/wiki/Jensen%27s_Device
+---------------
| [Algol 60] did not have a mechanism for declaring anonymous procedures.
+---------------
Quite correct, but completely off the mark. While an Algol 60 *user*
could not declare an anonymous procedure, the *implementation* of an
Algol 60 compilers required the ability for the compiler itself to
generate/emit internal anonymous procedures, to wit, the above-mentioned
thunks, sometimes creating them dynamically during the procedure call.
[Actually, a pair of them for each actual argument in a procedure call.]
+---------------
| That, like the incorporation of machine code inserts, would have been
| a compiler-specific extension, so it is a terminological mistake to
| refer to it without specifying the implementing compiler.
+---------------
Again, "incompetent, irrelevant, and immaterial" [as Perry Mason used
to so frequently object during trials]. Thunks were not "extensions" to
Algol 60 compilers; they were part of the basic implementation strategy
*within* Algol 60 compilers, necessary because of the semantics required
by call-by-name.
Basically, in Algol 60, each parameter must be passed [in general,
that is, one can optimize away many special cases] as *two* closures --
conventionally called "thunks" by Algol 60 compiler writers -- one
for "getting" (evaluating) and the other for "setting" the parameter
[if the parameter was a "place" in Common Lisp terms, else an error
was signalled]... IN THE CALLER'S LEXICAL ENVIRONMENT!!
The big deal was two-fold: (1) each time a formal parameter was
*referenced* in a callee, the expression for the actual parameter
in the caller had to be *(re)evaluated* in the *caller's* lexical
environment, and the value of that (re)evaluation used as the
value of the referenced formal parameter in the callee; and
(2) if a variable appeared twice (or more) in a parameter list,
say, once as a naked variable [which is a "place", note!] and again
as a sub-expression of a more complicated parameter, then setting
the formal parameter in the *callee* would *change* the value of
the actual parameter in the caller(!!), which in turn would change
the value of the *other* actual parameter in the caller the next time
it was referenced in the callee. The above-referenced "Jensen's Device"
shows how this can be used to do "very tricky stuff". A simpler and
shorter example is here:
http://www.cs.rit.edu/~afb/20013/plc/slides/procedures-07.html
Because the actual parameters in the callee had to be evaluated
in the *caller's* lexical environment -- and because Algol 60 was
fully recursive, allowed nested procedure definitions, and could
pass "local" procedures as arguments -- efficient implementation of
Algol 60 procedure calls almost necessitated placing the bodies
of the compiler-generated actual parameter thunks on the caller's
dynamic stack frame [or at least call instructions *to* the thunks
which could pass the current lexical contours as sub-arguments].
Knuth's nasty "man or boy test" stressed this to the limit:
http://en.wikipedia.org/wiki/Man_or_boy_test
-Rob
p.s. IIRC [but it's been a *long* time!], the ALGOL-10 compiler
for the DEC PDP-10 passed each actual parameter as the address of
a triple of words, of which the first two were executable and the
third could be used to store a variables value (simple case) or
to pass the lexical contour (more complicated case). When the
callee needed to reference (evaluate) an argument, it used the
PDP-10 XCT ("execute") instruction to execute the first word of
the block, which was required to deliver the value to a standard
register [let's say "T0", just for concreteness], and if the callee
wanted to *set* an argument, it executed the *second* word pointed
to by the passed address, with the new value also in a defined place
[again, let's use T0]. So to implement "X := X + 1;" in the callee,
the compiler would emit code like this:
MOVE T1,{the arg (address) corresponding to "X"}
XCT 0(T1) ; fetch the current value of X into T0.
ADDI T0, 1 ; increment it
XCT 1(T1) ; execute the "setter" for X.
Now in the case where the actual parameter in the caller was a
simple global variable, call it "Y", then the address passed as
the arg could be the following "YTHNK" in static data space:
YTHNK: MOVE T0,.+2 ; one-instruction "getter"
MOVEM T0,.+1 ; one-instruction "setter"
Y: BLOCK 1 ; the actual place where the value "Y" lives
Whereas if the argument being passed were some more complicated
expression, such as an array reference or a reference to a local
procedure in the caller, then the 3-word arg block would be passed
on the stack and the passed address would point to this [possibly
dynamically-constructed] triple, where PUSHJ is the PDP-10 stack-
oriented subroutine call instruction:
PUSHJ P,{lambda-lifted getter code}
PUSHJ P,{lambda-lifted setter code}
EXP {lexical contour info needed for getter/setter to work}
Efficient for the simple case; slow-but-correct for the messy case.
-----
Rob Warnock <rpw3@rpw3.org>
627 26th Avenue <URL:http://rpw3.org/>
San Mateo, CA 94403 (650)572-2607
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
From: Perl-Users-Request@ruby.oce.orst.edu (Perl-Users-Digest Admin)
Subject: Digest Administrivia (Last modified: 6 Apr 01)
Message-Id: <null>
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End of Perl-Users Digest V11 Issue 1738
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