Issue 3

by Alaric Snell-Pym

2010-09-10 +0000

0. Introduction

Welcome to issue 3 of the Chicken Gazette!

There is work afoot to improve the build system, so we would very much like testing and feedback on the Cygwin, Solaris and Haiku ports. If you have access to any of these operating systems, please check out the make-refactoring branch of chicken-core from git and tell us if it works well for you; append any feedback to ticket 167 in trac.

1. Infrastructure

Salmonella is now running on Chicken 4.6.0rc1, and a drive to attract attention to broken eggs has brought our current failing egg count down to a mere FOUR, which may well be the lowest it's ever been (since we only had four eggs, at least).

For those who find git is not to their taste, there is now a regularly-updated bzr mirror of the chicken core at, and the git repository can also be accessed via the git protocol (as well as the existing git-over-http) at git:// Now you have no excuse not to track the development releases!

2. The Hatching Farm - New Eggs & The Egg Repository

There have been no new eggs this week, but many commits - most notably, Ivan Raikov has done a great job of moving egg documentation to the wiki from various legacy formats, so they'll all appear in chicken-doc and chickadee.

3. The Core - Bleeding Edge Development

The week started with Felix fixing a bug reported by Sven Hartrumpf, where -optimize-level 2 was causing chicken to die with "Error: (=) bad argument type - not a number: #f". Not to be outdone, Felix then went and fixed the Cygwin build system, so even those of us unfortunate enough to be shackled to Windows can enjoy tasty Chicken goodness without needing to ssh into a real computer.

There's been non-stop fun out on the branches, too, with Peter Bex instigating a massive refactoring of the build system on the make-refactoring branch, and Felix doing optimizer and arithmetic work on the experimental branch and overflow-detection branches.

4. Chicken Talk

The Chicken Users list has been fairly busy this week, starting with the aforementioned optimizer bug report. An issue was raised with the tinyclos egg using the -no-procedure-checks-for-toplevel-bindings flag to csc, only introduced in version 4.5.2, while 4.5.0 is the latest stable release. It was pointed out that chicken-install will gladly install older versions of eggs with the following syntax:

chicken-install tinyclos:<version>

However, in future, it would probably be a good idea if egg authors held off of releasing versions of their eggs that use features from development builds of Chicken!

Alaric Snell-Pym (your faithful Gazette editor this week) suggested adding links to browse the source code and to discuss each egg on the egg index page; there was a positive response to the idea of the source code links as long as it doesn't clutter things, but it was felt that users should be encouraged to raise egg suggestions and questions on the mailing list. A patch is in the pipeline to add the source browser links, so we can decide if it's a good idea in practice.

5. Omelette Recipes - Tips and Tricks

One of my favourite eggs is fmt. There are two reasons for this. One is that I like what it does; neat text formatting is difficult, and is usually a distraction from the core problem your application is trying to solve; the fmt egg makes things like columns and justification easy. The second is that I like how it works.

Common Lisp has the format function, which works much like C's printf function: a format string is provided containing static text with special control sequences where values should be inserted at run time. Naturally, format far exceeds printf in power; it being Common Lisp, they of course had to include such features as Roman numerals alongside more immediately useful features such as formatting lists neatly. However, format is not extensible; it has a fixed library of control sequences that tell it how to format things like lists, numbers, and strings; and various formatting operations such as left or right alignment, padding to fixed widths, and so on. People who wish to have different formatting modes for arbitrary objects (such as user-defined types), or specific formatting operations (such as flowing text into a circular frame), had to abandon format and write their own from scratch.

And that's no fun.

fmt abandons the "format string" approach, and is instead based on a library of formatting combinators. Thanks to this architecture, new combinators can be defined in terms of the existing combinators. It comes with a rich library of combinators, supporting such things as SRFI-38 compliant pretty-printing of sexprs with shared structure, the full range of number formats (from customisable decimal points, thousand separators and scientific notation through to - you guessed it - Roman numerals (in two flavours!)), list formatting, decimal alignment for tables of numbers, trimming and padding to align columns (with configurable behaviour for values that won't fit in their columns, including using an ellipsis to warn the reader of omitted content), and support for wrapped columns of multi-line values (including justification).

Perhaps my favourite example from the manual is:

(define func
  '(define (fold kons knil ls)
     (let lp ((ls ls) (acc knil))
       (if (null? ls) acc (lp (cdr ls) (kons (car ls) acc))))))
(define doc
   "The fundamental list iterator.  Applies KONS to each element "
   "of LS and the result of the previous application, beginning "
   "with KNIL.  With KONS as CONS and KNIL as '(), equivalent to REVERSE."))
(fmt #t (columnar (pretty func) " ; " (justify doc)))

The glorious output of this is:

(define (fold kons knil ls)           ; The    fundamental   list   iterator.
  (let lp ((ls ls) (acc knil))        ; Applies   KONS  to  each  element  of
    (if (null? ls)                    ; LS  and  the  result  of the previous
        acc                           ; application,   beginning  with  KNIL.
        (lp (cdr ls)                  ; With  KONS  as  CONS and KNIL as '(),
            (kons (car ls) acc)))))   ; equivalent to REVERSE.

The fmt egg makes beautifully-formatted text output from your applications easy. Give it a try!

6. About the Chicken Gazette

The Gazette is produced weekly by a volunteer from the Chicken community. The latest issue can be found at or you can follow it in your feed reader at If you'd like to write an issue, check out the instructions and come and find us in #chicken on Freenode!

The chicken image used in the logo is kindly provided and © 2010 by Manfred Wischner