iterate-devel December 2005

iterate-devel@common-lisp.net

5 participants
7 discussions

[iterate-devel] ASDF installability of the package
by Ignas Mikalajunas 07 Jan '06

07 Jan '06

Hi, i wanted to download the most current iterate, but i am geting 403 error. Should I just use 1.4.0 or is that a bug ? Ignas Mikalajūnas

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[iterate-devel] 403 FORBIDDEN
by Rune Nesheim 26 Dec '05

26 Dec '05

http://common-lisp.net/project/iterate/releases/iterate_1.4.1.tar.gz 403 FORBIDDEN, this also means asdf:install is broken for iterate.

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Re: [iterate-devel]/[series-users] collect-tail ?
by Hoehle, Joerg-Cyril 20 Dec '05

20 Dec '05

Chris Dean wrote: >[1] The anatomy of a loop: a story of scope and control. > Olin Shivers. > http://www.cc.gatech.edu/~shivers/citations.html#loop > >[2] Eager Comprehensions in Scheme: The design of SRFI-42 > Sebastian Egner > http://www.deinprogramm.de/scheme-2005/program.html Thank you very much for these pointers. I'm very happy to see research in iteration in a way that is potentially useable for CL (unlike iteration constructs in many other languages). I'm still looking for the ideal construct myself. :-) >This is my standard looping question in any language: Read the last N >lines of a file, transform them, filter them, and return the unique >elements. Not trivial, even with SRFI-42. It's interesting how Iterate and SRFI-42 appear somewhat inside-out: one has COLLECT buried somewhere inside the body, the other right upfront (list-ec). OTOH, one has the form to be collected buried deep inside, the other right next to COLLECT. Good reading. Regards, Jorg Hohle

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Re: [iterate-devel]/[series-users] collect-tail ?
by Hoehle, Joerg-Cyril 19 Dec '05

19 Dec '05

Chris, since you're asking similar questions in series-users and iterate-devel, I'm starting to wonder whether you're going to write a paper on comparisons of some looping frameworks? :-) >how do I go about collecting the last N elements of anything? > (iter (for line :in-file my-file :using #'read-line) > (collect-tail line :how-many 10)) If 10 is known at macro-expansion time, you can always write a macro that expands to a series of 10 uses of PREVIOUS in Iterate, or 10 consecutive latches in Series. I.e., IMHO there are always two ways, either with series of iterate: a) Either take a code generation approach and create code that latches (= delay by one) N times, b) Or take a functional approach, implement a ring datastructure and use that. The former looks like a better use of Series: it could be a series of the 10 last values (as a list, or 10 series of values farther and farther behind). In/After the last iteration, you'll have the 10 last values. As to which approach is better... Probably you wouldn't want to generate code for the last 100 values. BTW, you'll have to defined what happens when less than 10 iterations were taken. Straight-forward code is likely to return (val1 val2 nil nil ...6xnil), whereas one could wish for (val1 val2) with only 2 iterations. Regards, Jorg Hohle.

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[iterate-devel] collect-tail ?
by Chris Dean 15 Dec '05

15 Dec '05

How would I go about reading the last 10 lines in a files? Or more generally, how do I go about collecting the last N elements of anything? I'm looking for advice on the "right way" to do this using iterate. On way would be to write collect-tail that just kept the last N elements: (iter (for line :in-file my-file :using #'read-line) (collect-tail line :how-many 10)) Is this a good way? Regards, Chris Dean

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[iterate-devel] Between-each, FORMAT's ~^ and code-walking
by Hoehle, Joerg-Cyril 09 Dec '05

09 Dec '05

Mészáros Levente wrote: >> Would you like to show more elaborate loop examples? >Let's say one has a list and one wants to transform it into a >string by transforming each element to a string and putting a >comma between them. >(concatenate-as-string > (iter (for e in l) > (except-first-time (collect ", ")) > (collect (as-string e)))) I recently came across that article about Lispy FORMAT replacements and started wondering how to nicely implement FORMAT's "~^" idiom. http://www.cs.yale.edu/homes/dvm/format-stinks.html BTW, I haven't seen the code for McDermott's out macro, but I expect it to be subject to code-walking problems similar to Iterate, series and other packages that depend on traversing code. Why? consider one example from the above article: (out "#<Foo " (Foo-label f1) (:q ((eq (Foo-status f1) ':abnormal) "?")) (:e (dolist (x (Foo-contents f1)) (:o " " x))) ">") Do you see the :o keyword inside the dolist? I think keywords are constants and cannot be locally bound (using MACROLET). Therefore, I believe the OUT macro needs to code-walk its body to track down all uses of :o and insert the replacememt code. Had a non-constant symbol been used therein, then MACROLET could have been used and the implementation of the macro out would (presumably) be clean. In any case, ~^ is quite different from *-first-time. It's more like an early test of loop termination. The macro out does not propose an idiom for that. The examples just repeat the termination test, as in (defun print-xapping ...) ... (do ((d ... (cdr d))) ... (:q ((not (null (cdr d))) " "))))) Repeating the test makes it unable to use the much more readable DOLIST instead of DO, and therefore must also use (CAR d) to access the elements. Reading the full paper (ytools) instead of the short FORMAT critique, it appears to me that OUT is no silver bullet either. It has its own set of controls: :a, :e, :t, :i>, :i<, :f, :v, :pp-block etc., so it's still complex to grok. I found the difference more appealing between e.g. the sexp-based regular expression notation (IIRC there's a Scheme SRFI about it) that the error-prone flat string syntax. BTW, McDermott's diver&snorkeler macro design pattern is interesting. Regards, Jörg Höhle

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Re: [iterate-devel] Between-each
by Hoehle, Joerg-Cyril 02 Dec '05

02 Dec '05

Hi, Mészáros Levente wrote: >I may be wrong about this, but I could not find support for a >quite commonly used loop pattern, namely when you want >something to be evaluated between each loop cycles. Please accept my apology for responding that late. I felt a little uncomfortable (see below) and did not quite know how to reply. >(def-special-clause BETWEEN-EACH (between) > (return-code :body (list (if-1st-time nil (list (walk-expr between)))))) Correct code (like implementation of IF-FIRST-TIME). >Maybe I'm wrong, could somebody tell how to do this with >iterate? If there's no support for this perhaps you could put >something like this into the main branch. You could use a macro-substitution and expand to the exported and documented IF-FIRST-TIME and DEFMACRO-CLAUSE, instead of using package internals like return-code. Your implementation shows that there's the same relationship between IF-FIRST-TIME and your BETWEEN-EACH like there's between WHEN and UNLESS. So why not add it, even it would be redundant to purists? However, given that analogy, I find the given name quite misleading, as it's very different from AFTER-EACH. >And it works like: >(iter (for i from 1 to 3) (between-each (collect (+ i 100))) > (collect i)) >(1 102 2 103 3) Hmm, I feel uncomfortable with the name, given the functionality you show. "Between" is something I'd expect to happen after one iteration, while you use it within the body. I.e., my wording shows I'm thinking in terms of AFTER-EACH. Well, there's AFTER-EACH, which is subject to code movement, but wouldn't it work for you? Another question is: how does this extension behave when used outside the top-level of the loop. Does the given name adequately reflect the functionality? E.g. (iter (for i...) (if (oddp i) (between-each (collect i)))) What would a reader expect as value from such a form? What about BUT-FIRST[-TIME] as a name? Would you like to show more elaborate loop examples? Regards, Jörg Höhle.

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iterate-devel December 2005