A Mudballs Update

Yes, I know it's late but better late than never right.

Anyway, I have just uploaded the 'Christmas Cheer' release of mudballs which, unfortunately, will require a fresh install of mudballs for existing users as there was a rather egregious oversight regarding the updating of systems.

Noteworthy Features

• A publicly editable wiki has now been made available at http://redmine.mudballs.com/wiki/mudballs/   New pages can be created by opening the appropriate URL. For example, http://redmine.mudballs.com/wiki/mudballs/hunchentoot will  show an option for creating a new page. 
• The start of a mudballs FAQ can be found on it's wiki page: http://redmine.mudballs.com/wiki/mudballs/FAQ.
  
• down-casing of pathnames has been fixed. Down-casing will now only happen for components named with symbols.
  
• New versions of all systems, including core systems such as :cl-ppcre, can now be updated without having to reinstall mudballs.
  
• (mb:install :cl-ppcre :file "/path/to/file") now works.
  
• The output path of component is now calculated correctly (including honoring the :fasl-output-root preference).
  
• Uninstalled systems are no longer considered  for an operation if there is an installed version of the system present unless explicitly requested using the :version keyword.
  
• The fasl-path of system definition files is no longer the same as components of a system as this was conflicting with the output of compiling components.
  
• And other small fixes

As always mudballs is available for download from the releases directory and instructions can be found here.

Please let me know if any server on mudballs.com is not responding as my hosting provider is being a little flaky of late.

Thanks to the following people for reports and ideas.

- Magnus Malm

- Luke Renn

- Leigh Smith

Announcing Mudballs

 This post is to announce the release of Mudballs, a collection of Common Lisp code for managing systems.  It is currently in an early stage of development and still has a long way to go but is currently able to compile,  load, document, download and install systems across Windows, Linux and Mac OSX. Mudballs supports the following implementations 

• Lispworks on Mac OSX, Linux and Windows.
  
• SBCL on Mac OSX and Linux.
• CMUCL on Mac OSX and Linux.
• CLISP on Linux and Windows (Mac OSX as well provided  you have FFI).
• ClozureCL/OpenMCL on Mac OSX, Linux and Windows.
• AllegroCL on Mac OSX, Linux and Windows.

 

 As it currently stands it is not ASDF compatible (not ideal, I know) but ASDF support is planned for the future. It is available from http://mudballs.com  which contains enough information to get the intrepid lisper on his or  her way.

 

 As a small taste, the following is now possible from a freshly installed Lisp with Mudballs loaded.

> (mb:install :hunchentoot)
> (hunchentoot:start-server :port 8080)

P.S.  Prizes for anyone that can come up with a logo which doesn't look like a pile of excrement.

Renaming files in Common Lisp.

So I ran across this while going through my morning catchup routine and thought it could do with some clearing up.

The part of the post I'm actually interested is this.

When Haskell can compete on those types of problems, it'll be easier to induce people to learn it. (Same with CL, my fav language....)

Now, bonus points for proclaiming CL as being his favorite language, but minus 10 billion for continuing the meme that CL is somehow unsuited for writing[1] these kinds of simple software (for whatever definition of simple you have).

One of the examples given is "I have a bunch of files, and I want to rename them all according to some pattern." and as it so happens translate-pathname[2] makes this wonderfully simple.

(defun rename-files (from to)
 (dolist (file (directory from))
   (rename-file file (translate-pathname file from to))))

And thats it, 3 lines of code, or for our simple testing purposes

(defun show-rename-files (from to)
 (dolist (file (directory from))
   (format t "Renaming ~A to ~A~%" file
           (translate-pathname file from to))))

(show-rename-files "/usr/share/pixmaps/*.xpm" "/usr/share/pixmaps/backup-*.xpm")

The funny thing is that this isn't secret knowledge but is pulled straight from the Hyperspec (see the examples).

----
[1]: Please note, I said 'writing' them, not 'creating a 2k binary' of them, please people CL /= Unix.
[2]: Granted, the behavior of translate-pathname isn't specified in detail by the spec but that doesn't mean we cannot use it.

This post brought to you by Lispworks 5.1, clisp 2.41 and SBCL 1.0.12

Case Conversion Considered Useful

One of the stranger[1] features of Common Lisp is that the CL reader, by default, will convert symbols to uppercase[2] which can be a little surprising to newcomers, and inevitably leads misconceptions regarding case (in)sensitivity.

One of the advantages of this automatic case conversion is that it allows us to use case as syntactic markers.

Here's a simple example (ignore the non idiomatic use of CL).

(defun filter (test list)
 (let ((result ()))
   (dolist (elt list result)
     (when (funcall test elt)
       (push elt result)))))

Did you notice the return form?
This happens to be one of those constructs that is quite easy to overlook when reading through code, it doesn't happen often but it does happen[3].

However, if we change it to this.

(defun filter (test list)
 (let ((result ()))
   (dolist (elt list RESULT)
     (when (funcall test elt)
       (push elt result)))))

the result form 'leaps' out of the page which makes it very difficult to miss.

It's the code equivalent of wearing a silly hat.

---

1: Stranger, as in, 'This isn't like C/Java/Python/Ruby'.
2: This is only the default and can be changed using readtable-case
3: Well it happens to me, ok.

The 'pre Arc' Arc

Seeing that arc is the word on everyones lips I thought I'd take a quick peek.

In Summary.
- data in the functional position is interesting.
- [] function syntax is neat (and almost as nice as the #L syntax in iterate)
- foo:bar for function composition reads quite nicely (once you get out of the CL mindset)

The rest is kind of 'meh' and then i realized, wait a second, a Lisp1 with more Lisp than Scheme and unhygienic macros,  I've seen that before and I had, it is called rep.  This is the Lisp that powers sawfish which (and someone correct me if I'm wrong) was the default window manager for GNOME for quite some time.

This was actually the Lisp that I cut my teeth on way back in 2001 (Grief, I can't believe it was that long ago)  and looking back on it brings back some fond memories and reminds me how full featured it was (especially for something at version 0.17), to list some of them:

• Profiler
• Module system (modelled on Scheme48)
• Tail call elimination
• Byte Compiled
• First class Continuations
• Regexes
• Threading
• Good access to OS 
• Ability to load .so files
• Bindings to mysql
• Built in documentation via the ,desc operator

and Most importantly it has apropos, god knows why arc is missing this.

Ruby Quiz 144 (in CL)

There was a small posting on c.l.l asking if anyone felt like completing Ruby quiz 144 in CL and after eric's solution I thought I'd give it a go.

This needs :cl-ppcre and :alexandria (and :lisp-unit to run the tests)
Apologies for formatting screwiness.

(defpackage :time-window (:use :cl :cl-ppcre :alexandria)
  (:export #:in-window-p))

(in-package :time-window)

;(defparameter *window* "Sat-Mon; Mon Wed 0700-0900; Thu 0700-0900 1000-1200")

;; This works by converting a spec (like the one above) into it's seperate components (split by ;)
;; and converting each spec into distinct time and day parts (expanding day ranges as we go)
;; so the above would be converted into the following
;; ((nil                       ("Sat" "Sun" "Mon"))
;;  (("0700-0900")             ("Mon" "Wed"))
;;  (("0700-0900" "1000-1200") ("Thu")))
;; We can then walk through each converted spec ensuring that the time specified falls into
;; the time/day specified.

(defun in-window-p (time window)
  (some (lambda (spec)
          (every (lambda (part)
                   (if (null part)
                       t ;; since (some (constantly t) ()) is nil
                       (some (curry 'time-within time) part)))
                 spec))
        (mapcar (lambda (split)
                  (group-by-type (split " " (string-trim " " split))))
                (split ";" window))))

(defun group-by-type (list)
  (loop for spec in list
        :when (time-range-p spec) :collect spec :into times
        :when (single-day-p spec) :collect spec :into days
        :when (day-range-p spec) :append (days-of spec) :into days
        :finally (return (list times days))))

(defparameter *days*
  '(("Mon" . 0) ("Tue" . 1) ("Wed" . 2) ("Thu" . 3) ("Fri" . 4) ("Sat" . 5) ("Sun" . 6)))

(defparameter *day-ring* (let ((list (copy-list *days*)))
                           (setf (cdr (last list)) list)
                           list))

(defun single-day-p (spec)
  (assoc spec *days* :test 'string=))

(defun day<-spec (spec)
  (cdr (single-day-p spec)))

(defun day-range-p (spec)
  (and (= (count #\- spec) 1)
       (every 'single-day-p (split "-" spec))))

(defun days-of (spec)
  (assert (day-range-p spec))
  (destructuring-bind (start stop) (split "-" spec)
    (loop :for (day . nil) :in (member start *day-ring* :key 'first :test 'string=)
          :collect day
          :until (string= day stop))))

(defun single-time-p (spec)
  (every 'digit-char-p spec))

(defun time-range-p (spec)
  (and (= 1 (count #\- spec))
       (every 'single-time-p (split "-" spec))))

(defun time-in-range (hour minute start stop)
  (flet ((to-mins (x) (+ (* 60 (parse-integer (subseq x 0 2)))
                         (parse-integer (subseq x 2 4)))))
    (<= (to-mins start) (+ (* 60 hour) minute) (1- (to-mins stop)))))

(defun time-within (time spec)
  (multiple-value-bind (sec minute hour date month year day)
      (decode-universal-time time 0)
    (declare (ignore sec date month year))
    (cond ((single-day-p spec) (= day (day<-spec spec)))
          ((time-range-p spec)
           (apply #'time-in-range hour minute (split "-" spec))))))


;;; and a small test package
(defpackage :time-window.tests (:use :time-window :lisp-unit :cl))
(in-package :time-window.tests)

;; Tests
(define-test window-tests
  (let ((window "Sat-Sun; Mon Wed 0700-0900; Thu 0700-0900 1000-1200"))
    (flet ((in (sec hour date month year)
             (in-window-p (encode-universal-time 0 sec hour date month year 0) window)))
    (assert-false (in 0 8 25 9 2007))
    (assert-true  (in 0 8 26 9 2007))
    (assert-false (in 0 11 26 9 2007))
    (assert-false (in 59 6 27 9 2007))
    (assert-true (in 0 7 27 9 2007))
    (assert-true (in 59 8 27 9 2007))
    (assert-false (in 0 9 27 9 2007))
    (assert-true (in 0 11 27 9 2007))
    (assert-true (in 0 11 29 9 2007))
    (assert-true (in 0 0 29 9 2007))
    (assert-true (in 59 23 29 9 2007))
    )))

(define-test window-tests2
  (let ((window "Fri-Mon"))
    (flet ((in (date month year)
             (in-window-p (encode-universal-time 0 0 0 date month year 0) window)))
      (assert-false (in 27 9 2007))
      (assert-true (in 28 9 2007))
      (assert-true (in 29 9 2007))
      (assert-true (in 30 9 2007))
      (assert-true (in 1 10 2007))
      (assert-false (in 2 10 2007)))))

(run-tests)

Nothing flashy but it does remind me how useful circular lists can be.
Comments, as always, are welcomed.

---
This post brought to you by Lispworks 5.0.2

Closures + Lambda < CLOS

There's a blog post floating around the web[1] on how Closures + Lambda make up all the OO programming tools you'll ever want or need. Now this is a long running theme[2] in the Lisp family and really is a testament to how flexible Common Lisp (or any other language which shares these traits) is

.... however ....

the majority of these are for pedagogical purposes[3] and should never be seriously
compared with a fully fledged object system. It's seems to be in vogue to consider
CLOS elephantine[4] and complex but the truth is that at the surface CLOS is wonderfully simple.

We have classes with slots (read instance variables) created with defclass, we create
instances of these classes with make-instance. We access (and change) the slots of these
instances using slot-value and create methods for the classes using defmethod.

Simple, yes? Not complex or elephantine, Yes?

You can read more of course (all in the CLHS) and discover the object initialization protocol
and how the classes of objects can be changed on the fly, you can find out how to customize
the initialization of your classes and add accessors to your slots.
You can dig deeper and you'll discover the MOP and discover how to change the behaviour of
slot access and class definition.

But remember that you do not need to understand any of this in order to
define classes, create instances, access slots and define methods!

So next time you are rolling your own Object System because someone considers CLOS too slow,
or too large, stop and give CLOS a try, you may just like it.


--------------------
[1] : See here and here .
[2] : And is implemented in PAIP and On Lisp among others.
[3] : For a full OO implementation in CL see KR which is a prototype based object system with valuepropogation.
[4] : Or big, slow[5] or klunky
[5] : This myth has officially been debunked.