Trying to understand the macroexpansion of an iterate clause

Dear List

I am reading the iterate manual and have come across this form:
  (iter (generating (key . item) in '((a . 1) (b . 2) (c . 2)))
	(collect (next key))
	(collect (next item)))
The manual says that the form returns (a 2 c).

I have pasted the result of (macroexpand-1  form), where form is the
above iter form, but I have removed all the `#:' prefixes of the
variables, to http://paste.lisp.org/+31RO (the O is the
upper-case letter oh).

I have dry run the expanded code 3 times and I still do not understand
how the variable result21 is bound to a list whose length is > 1. The
only places in the expanded code where result21 is bound to a new value
consists of a SETQ with the value bound to temp24. During my dry
running, it appears that temp24 is bound to, successively, (a) (2)
(c). Using the Stepper tool, I have discovered that the value result21
is bound to, changes when end-pointer23 is bound to "(a 2)", but the
value in end-pointer23 is never used to change another variable.

So what changes the value of result21? And where?

Your help would be appreciated.

Sincerely
-- 
Dr Sian Mountbatten
http://www.poenikatu.co.uk/
Associate member of the FSF no. 10888
Asocia membro de la Libera Programara Fonduso n-ro 10888

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Re: Trying to understand the macroexpansion of an iterate clause

On 04/23/14 10:44, Sian Mountbatten wrote:
> I am reading the iterate manual and have come across this form:
>   (iter (generating (key . item) in '((a . 1) (b . 2) (c . 2)))
> 	(collect (next key))
> 	(collect (next item)))
> The manual says that the form returns (a 2 c).
> 
> I have pasted the result of (macroexpand-1  form), where form is the
> above iter form, but I have removed all the `#:' prefixes of the
> variables, to http://paste.lisp.org/+31RO (the O is the
> upper-case letter oh).
> 
> So what changes the value of result21? And where?

The code updating RESULT21 is the following form:

 (SETQ END-POINTER23
       (IF RESULT21
           (SETF (CDR END-POINTER23) TEMP24)
         (SETQ RESULT21 TEMP24)))

TEMP24, RESULT21, and END-POINTER23 all have the same initial value: the
cons '(A . NIL).  During subsequent evaluations the above form adds
items to the RESULT21 list in-place by replacing the cdr of the last
cons with a list containing each new item.


Mike

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Re: Trying to understand the macroexpansion of an iterate clause

Sian Mountbatten <poenikatu@fastmail.co.uk> writes:

> On 2014-04-23 19:09, Miller, Bradford W (GE Global Research) wrote:
>> You need to find two friends. One to hit you on the back of the head
>> with a chine ual, and the other to reboot your lisp machine.
> What is a "chine ual"? 

A chine nual, is a book with a big title written on the cover like this:

             +--------------+
             |     |  | LISP|
             |     |  |     |
             |     |MA|CHINE|
             |     |  |     |
             |     |MA|NUAL |
             +--------------+

so when the book is folded, you can read CHINE NUAL:

             ------+
             | LISP|
             |     |
             |CHINE|
             |     |
             |NUAL |
             ------+

http://i.imgur.com/8s2fPJg.jpg


-- 
__Pascal Bourguignon__
http://www.informatimago.com/
"Le mercure monte ?  C'est le moment d'acheter !"

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RE: Trying to understand the macroexpansion of an iterate clause

That is great! :)

My copy of David Moon's book looks quite different, as I recall. Must be the Symbolics reprinted edition ... I have to go find it and look! :)

Z

Syed Zaeem Hosain | Chief Technical Officer
Aeris Communications, Inc.
Syed.Hosain@aeris.net
o: +1 408 557-1905 | f: +1 408 557-1925 | twitter: @AerisCTO | blog: http://www.aeris.com/blog

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-----Original Message-----
From: owner-lisp-hug@lispworks.com [mailto:owner-lisp-hug@lispworks.com] On Behalf Of Pascal J. Bourguignon
Sent: Wednesday, April 23, 2014 12:41 PM
To: Sian Mountbatten
Cc: lisp-hug@lispworks.com; Miller, Bradford W (GE Global Research)
Subject: Re: Trying to understand the macroexpansion of an iterate clause


Sian Mountbatten <poenikatu@fastmail.co.uk> writes:

> On 2014-04-23 19:09, Miller, Bradford W (GE Global Research) wrote:
>> You need to find two friends. One to hit you on the back of the head 
>> with a chine ual, and the other to reboot your lisp machine.
> What is a "chine ual"? 

A chine nual, is a book with a big title written on the cover like this:

             +--------------+
             |     |  | LISP|
             |     |  |     |
             |     |MA|CHINE|
             |     |  |     |
             |     |MA|NUAL |
             +--------------+

so when the book is folded, you can read CHINE NUAL:

             ------+
             | LISP|
             |     |
             |CHINE|
             |     |
             |NUAL |
             ------+

http://i.imgur.com/8s2fPJg.jpg


--
__Pascal Bourguignon__
http://www.informatimago.com/
"Le mercure monte ?  C'est le moment d'acheter !"

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Lisp Hug - the mailing list for LispWorks users lisp-hug@lispworks.com http://www.lispworks.com/support/lisp-hug.html



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