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[cdr-discuss] About the CDR process
by Tobias C. Rittweiler 16 Nov '08

16 Nov '08

Hi, 1. quoting CDR 4, ``Common Lisp Document Repository (revised)'': ``There will be an initial period of six weeks in which you can send us updated versions, for example to correct typos, etc., which will replace any older version with the same CDR number. You can negotiate with us a longer initial period, but the maximum length is one year.'' I think a default initial period of six week is way too short. I'd suggest a period of six _months_ instead. Otherwise, there's the danger that CDRs will be finalized which haven't received any real feedback. Feedback, that is public scrutination, is really crucial as I've found out myself while writing the With-Readtable-Iterator proposal. It is my impression that most people have the necessary spare time around semester breaks, and christmas. Extending the initial period to six months ensures that it always crosses one of these peak times. 2. I also suggest the permission to update finalized CDRs under the following constrain: A section talking about current practises CDR may be updated to reflect adoption of the documentation's content that has occured since the publication of the CDR. The change must not alter the meaning or the intent of the document. -T.

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[cdr-discuss] [RfC] WITH-READTABLE-ITERATOR
by Tobias C. Rittweiler 01 Nov '08

01 Nov '08

Request for comments. Including grammatical and stylistic corrections. -T. Issue: WITH-READTABLE-ITERATOR Forum: Common Lisp Document Repository (CDR) Status: Draft. References * CLHS 2.1.1 Readtables * X3J13 Issue #188 * `with-package-iterator' (macro) * `with-hash-table-iterator' (macro) Category: Addition. Edit History: 02-Oct-2008 by Rittweiler (Draft) Problem Description: Even though the ANSI Common Lisp standard provides simple getters for readtables (`get-macro-character', `get-dispatch-macro-character'), the standard does not provide any means to efficiently get at all the macro characters and dispatch macro characters defined in a readtable. The omission of any iteration facility for readtables makes readtables unneccessarily opaque, and keep users from writing libraries that try to deal with readtables in a general way. For example, the author discovered that this lack of an iteration form is the main obstacle to writing an otherwise portable library that establishes an organizational namespace for readtables akin to the namespace that is provided for packages. Proposal (WITH-READTABLE-ITERATOR:ADD-GENERATOR) Add a macro `with-readtable-iterator' that establishes a generator in its scope; each invocation of this generator returns a macro character or a dispatch macro character from the readtable the generator was established for--along side some additional information. A detailed specification of `with-readtable-iterator' can be found in the appendix of this document. Rationale The proposed macro `with-readtable-iterator' represents a general iteration facility for readtables that can be used to implement a variety of iteration forms. The proposal is closely modelled on the macros `with-hash-table-iterator' and `with-package-iterator'. The semantics of `with-readtable-iterator' should thus be intuitive to any experienced Common Lisp programmer. Notes The proposal does deliberately say nothing about the home-package of the symbol `with-readtable-iterator'. However, implementors are encouraged to export this symbol from their extensions package (often called "`EXT'") or another appropriate package--unless a later CDR document specifies a more explicit location. Current Practice No implementation the author is aware of provides a way to iterate through a readtable. The author implemented the proposal for SBCL (http://www.sbcl.org/) and sent the relevant patches upstream; the patches are currently waiting to be integrated into mainline. Ariel Badichi implemented the proposal for CLISP (http://clisp.cons.org/) and is going to send his work upstream shortly. Stephen Compall did an implementation for Clozure CL (http://ccl.clozure.com/) which needs to be somewhat revised to fully conform to the proposal as presented in this document. Cost to implementators The macro `with-readtable-iterator' should be straightforwardly implementable. Extrapolating from actual experience, people--who were previously not acquainted with the relevant code sections--were able to implement it in a couple of hours. Discussion Ariel Badichi proposed coalescing a generator's fourth return value (indicating if the returned character is a dispatch macro character) with its first return value (indicating if the generator is exhausted.) There is technically no reason that speaks against doing so; in fact, a generator would return one value less this way--which may lead to positive performance characteristics on register-anemic processor architectures. Stephen Compall and the author opposed such a change mostly for idiomatic reasons, as both `with-hash-table-iterator' and `with-package-iterator', the generator-establishing macros specified by the ANSI standard, return a purely boolean exhaustion flag as first value. In particular, `with-package-iterator' does _not_ coalesce the accessibility type (third return value) with the exhaustion flag (first return value.) The author notes that allowing `:terminating', and `:non-terminating' as valid MACRO-CHAR-TYPES was considered, but rejected for reasons of simplicity. It is not apparent that there is a real necessity for supporting these out of the box. Acknowledgements The author wants to specially credit Ariel Badichi and Stephen Compall which in spirit of true hackerism promptly agreed to hack an early version of the proposal into the implementations of their choice. Appendix -- Macro: with-readtable-iterator (name readtable &rest macro-char-types) declaration* form* => results Arguments and Values .................... NAME - A symbol. READTABLE - A form, evaluated once to produce a readtable. MACRO-CHAR-TYPE - One of the symbols `:macro-char', or `:dispatch-macro-char'. DECLARATION - A `declare' expression; not evaluated. FORMS - An implicit progn. RESULTS - The values of the FORMS. Description ........... Within the lexical scope of the body FORMS, the NAME is defined via `macrolet' such that successive invocations of `(name)' will return the macro characters, one by one, from the READTABLE. The order of the macro characters returned is implementation-dependent. An invocation of `(name)' returns the following five values: 1. A generalized boolean that is true if a macro character is returned. 2. A macro character that is defined in READTABLE. 3. A reader macro function of the macro character returned. 4. A generalized boolean that is true if the macro character is a dispatch macro character. 5. An association list between the "sub-characters" of the dispatch macro character and their reader macro functions. After all macro characters have been returned by successive invocations of `(name)', only one value is returned, namely `nil'. It is unspecified what happens if any of the implicit interior state of an iteration is returned outside the dynamic extent of the `with-readtable-iterator' form such as by returning some closure over the invocation form In spirit of CLHS 3.6, consequences are undefined if READTABLE is modified except for modification of the current macro character under traversal. Exceptional Situations ...................... Signals an error of type `program-error' if a MACRO-CHAR-TYPE is supplied that is not recognized by the implementation. See Also ........ Traversal Rules and Side Effects (CLHS 3.6), `with-package-iterator'

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[cdr-discuss] Test; Pending mails lost
by Tobias C. Rittweiler 14 Oct '08

14 Oct '08

Common-Lisp.net moved to a new server, and it seems that mails sent between a certain time frame didn't make it to the list. The archive can be found at http://common-lisp.net/pipermail/cdr-discuss/2008-October/date.html If you sent a mail, and cannot find it listed there, please consider resending it. -T.

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[cdr-discuss] Issues with DEFTYPE
by Marco Antoniotti 19 Aug '08

19 Aug '08

Hi I have the following DEFTYPE (deftype int-list () '(or null (cons integer int-list))) Then in LW this happens CL-USER 6 > (typep '(1 2 3) 'int-list) Stack overflow (stack size 15997). In Franz ACL the following happens instead CL-USER> (typep '(1 2 3) 'int-list) T CL-USER> (typep '(1 a 3) 'int-list) NIL (Sorry these are the only implementations I have at hand right now). Now: recursive types are not well understood by the CLHS, and it would seem that both implementations are somewhat "conforming". However, since we are in 2008, ACL behavior is the "correct" one, although it would seem that the people at Franz are stretching the CLHS. The question I have is the following: how do we go ahead and write a CDR that described ACL apparent behavior (i.e. how do we introduce "correct" recursive types in CL)? Note that I just want to start a discussion on this issue and collect comments and ideas. I am interested in a medium term discussion on the issue; I am not interested in responses like "use Qi" or "use F#/ Ocaml/Haskell etc" (as an aside, Haskell is my favorite of the bunch). Thanks -- Marco Antoniotti PS. There are also issues of "compilation" vs "run-time" environments to be taken into account. -- Marco Antoniotti

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[cdr-discuss] Issue CASE-TEST
by Leslie P. Polzer 13 Jul '08

13 Jul '08

Finally wrote something up. Please rip it apart where necessary. Pointers to efficient implementations that can be mentioned highly welcome. Thanks, Leslie

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Re: [cdr-discuss] Three RFCs
by Edi Weitz 06 Apr '08

06 Apr '08

On Tue, 18 Mar 2008 12:36:47 +0100, Pascal Costanza <pc(a)p-cos.net> wrote: > ...but that's ambiguous: Only if you insist on having a short form without parentheses. That's not a hard-and-fast requirement. > (case (thing :test #'=) > (42 'foo) > (4711 'bar)) > > What's the result of that form? Error: The variable THING is unbound.

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[cdr-discuss] [RfC] Issue: INSPECTOR-HOOK
by Tobias C. Rittweiler 20 Mar '08

20 Mar '08

Request for comments (this includes stylistic / spelling corrections) -T. Status: Draft Forum: Common Lisp Document Repository (CDR) Issue: INSPECTOR-HOOK References: INSPECT (function), *DEBUGGER-HOOK* (variable) Category: Addition Edit History: 20-Mar-2008 by Rittweiler (Draft) Problem Description: Cross-implementation Lisp programming environments such as SLIME or Climacs face the problem that the ANSI Common Lisp standard does not specify any way to hook into the inspection machinery of an implementation. Specifically, there is no portable way to install an inspector that is run when the function INSPECT is invoked. Proposal (INSPECTOR-HOOK:*INSPECTOR-HOOK*-VARIABLE) Add a variable: *INSPECTOR-HOOK* [VARIABLE] Value Type: A designator for a function of one argument (the object to be inspected), or NIL. Initial Value: NIL. Description: When the value of *INSPECTOR-HOOK* is non-NIL, an invocation of INSPECT in the dynamic-extent of this variable results in calling the value with the object that was originally passed to INSPECT. *INSPECTOR-HOOK* is not rebound before calling the function denoted by the value, i.e. it's bound to the same value as at the invocation of INSPECT; this is to allow inspectors to be defined recursively. The return value of INSPECT is independent of the return value of the denoted function, and remains implementation-dependent. Affected By: INSPECT See Also: *DEBUGGER-HOOK* Notes: It's possible to invoke the implementation's inspection machinery from within *INSPECTOR-HOOK* by binding it to NIL before invoking INSPECT. Rationale: This proposal was closely modelled on the specification of *DEBUGGER-HOOK*, and allows programs to install their own inspectors that are adapted to their respective domains. Notes: The proposal does deliberately say nothing about the home-package of the symbol *INSPECTOR-HOOK*. However, implementors are encouraged to export this symbol from their extensions package (often called "EXT") or another appropriate package---unless a later CDR document specifies a more explicit location. Current Practise: On at least SBCL, Clisp, and Clozure CL, it's possible to straightforwardly hook into their inspection machinery, albeit by mostly unexported and undocumented means. The documentation of Franz' Allegro CL states that an invocation of INSPECT runs a GUI inspector on the MS Windows operating system, and a text-based inspector on other operating systems, so it's very likely that they employ some hook mechanism internally. Cost to implementators: Negligible. Cost to user: None. The proposal is fully upward compatible. Cost of Non-Adoption: The problem, as described above, remains. Benefits: Slightly more powerful / convenient Lisp programming environments. Aesthetics: Inhibits the necessity to rely on implementation-dependent cruft.

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[cdr-discuss] Three RFCs
by Leslie P. Polzer 18 Mar '08

18 Mar '08

Hello folks, here are three CDR ideas that I would like to get your comments on: 1. Support a :TEST arg for (E)CASE. 2. Setup BACKQUOTE to be the backquote expansion object. I believe this is common implementor's practice. 3. Support extended feature tests. It would be nice to be able to say +(find-package 'zoo)(...) The complexity impact is none for #2, probably neglectable for #3 and should be moderate for #1. Leslie

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[cdr-discuss] CDR5 in alexandria
by Attila Lendvai 01 Mar '08

01 Mar '08

dear list, fyi, alexandria now has an almost full implementation of CDR5: http://common-lisp.net/project/alexandria/ http://common-lisp.net/cgi-bin/darcsweb/darcsweb.cgi?r=alexandria-alexandri… -- attila ps: no testsuite yet, patches are welcome.

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[cdr-discuss] CDR 5
by Gary King 01 Mar '08

01 Mar '08

I haven't looked over all the details but this seems like a very good idea to me and also seems clear, to the point and precise. nice work, -- Gary Warren King, metabang.com Cell: (413) 559 8738 Fax: (206) 338-4052 gwkkwg on Skype * garethsan on AIM

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