Schemely Blog

The Challenge of Scheme on Windows

2008-02-07T21:33:00.000-08:00

Free distributions of Lisp and Scheme are typically developed on Linux and work fully under Microsoft Windows only if Cygwin or Msys-mingw are installed to support them. This situation is probably fine for someone who already uses these shells for other free software packages. But not so great if one needs to install one of them for the sake of trying a Scheme or Lisp executable.

The authors and maintainers of Cygwin and Mingw deserve appreciation for providing their software. Nevertheless, this author has been frustrated while trying to use them consistently on different Windows computers. Part of the problem is that Windows is not a friendly environment for Unix-type tool chains.

Gambit-C Scheme offers best performance on Windows when compiled with GCC which in turn need Cygwin or Mingw. This author provides an Openwatcom Makefile for those Scheme enthusiasts who prefer not to use a Unix shell under Windows. Less performance but more convenient workflow.

You first need to obtain a prebuilt version of Gambit. Next, copy wmaker.scm which produces the Makefile when you type "gsi wmaker". Follow the directions on the wiki page for compiling Gambit from source.

Gambit-C Reviewed In Linux User

2008-01-09T21:31:00.000-08:00

Martin Howse says "Gambit-C pools the low-level power of C with the concise syntax and radical developement model of elegant Scheme". See Linux User and Developer Issue 61

Scheme Recursion and Closures

2008-01-02T21:51:00.000-08:00

Programmers of static languages such as Java and C++ may not be familiar with the topics of recursion and closures which are very important to Lispy languages. The online book An Introduction to Scheme Implementation is very helpful since it explains the underlying mechanisms in plain English. Other important topics include continuations and macros. These must wait for another day.

2007-09-22T22:26:00.000-07:00

Peter Seibel has written the excellent book Practical Common Lisp which is also available online..

Common Lisp tutorial

Linux User Reviews Chicken Scheme

2006-04-30T22:02:00.000-07:00

Linux User has a review of the Chicken Scheme Compiler/Interpreter. There is only 1.5 pages of text with a barely readable small green font on black screendump. Not much to impress someone unfamiliar with Lispy languages. However, I did see the word elegant so I guess it is a favourable review. This is the only magazine I have seen with periodic Lispy articles.

Scheme Sudoku Solver

2006-02-26T17:12:00.000-08:00

There is a Sudoku craze. Puzzles abound in books, newspapers, and web sites. For me, the charm fades as I wear out the eraser before the pencil when the inevitable backtracking occurs. But they are an interesting software exercise.

Every cell in a 9x9 sudoku puzzle is a member of 3 intersecting sets - a 3x3 box, a 9-cell row, and a 9-cell column. For a pending change in any cell, the rule must be applied to each of these 3 sets. Ergo, most of the effort is in applying the constraints.

I discarded my first attempt which looked too much like a 'C' program. The current one stores the puzzle in a vector. There are lists of vector indices representing different views of the puzzle space. The entire puzzle can be validated using the for-each idiom for a list of lists.

The source text can be found on this Schemely Wiki page.

What is Software?

2006-02-23T22:27:00.000-08:00

Quoting What is Software? in the Google search widget gives 130,000 or more hits. Most append another word such as Design, Assurance, Piracy and so on. I found no satisfactory answer to the basic question.

I program embedded systems using 'C' with a bit of Java and Perl on the side. My job title says 'Software Designer' but my duties include poking bits and bytes into registers of custom hardware. This certainly is programming but is it really software design? We know that software requires programming but does it follow that programming results in something called software? If so, consider FPGAs and CPLDs found in modern embedded systems. They are programmed by an engineer using a description language. They effect system functions but are not software or the result of software design. So it seems that programming, or giving instructions to a machine does not always result in software.

I think that abstraction is the most important property of software. For example, Java has a virtual machine to separate the hardware and computer operating system from the application. It provides an abstraction boundary. An email client program can be made to run on any computer or OS while being designed with almost any scripting or compiled language. So an email client is software. Scheme, Lisp, Eiffel, and others have some form of Foreign Function Interface to support an abstraction boundary. C/C++ does not so more designer diligence is required to maintain a clean abstraction.

Jack Reeves at DeveloperDotStar came to an interesting conclusion.

* Ultimately, real advances in software development depend upon advances in programming techniques, which in turn mean advances in programming languages. C++ is such an advance. It has exploded in popularity because it is a mainstream programming language that directly supports better software design.
* C++ is a step in the right direction, but still more advances are needed.

Apparently, he was not aware of dynamic languages such as Scheme.

Lispers looking fondly at Scheme

2006-01-19T22:44:00.000-08:00

Planet Lisp has a favourable review of PLT Scheme by Bill Clementson.

No Loop in Scheme

2006-01-15T16:53:00.000-08:00

Today I learned that loop is not a keyword in Scheme. I assumed it was from my habit of copying snippets like
'(let loop .... ) from working programs without taking time to RTFM. Since Scheme is a dynamic language, obfuscated forms will work. For example, known names can be repurposed:-


;; testing letrec
(define (monkeys n)
  (let letrec ( [x 3] )
    (display "Monkey\n")
    (if (> x 0)
 (letrec (- x 1) ))))
  
(monkeys 0)
(exit)

Dorai Sitaram provides a clear example in section 6.2 of Teach Yourself Scheme.

sudoku puzzle investigation

2006-01-10T22:19:00.000-08:00

Depth-First-search

Scheme Foreign Functions with Chicken

2005-12-27T19:00:00.001-08:00

I like programming in 'C'. It is great for the low-level hardware peeks and pokes but rather tedious for the high-level application. I would like my programming language to provide a certain abstraction boundary where the platform fiddly-bits are hidden from the application but still accessible when the time is appropriate. Scheme does that very well with it's Foreign Function Interface.

Chicken offers several interesting FFI variants. I present a simple example in this post. Why is it called Chicken? Well, it emits 'C' code and calls GCC or other compiler to compile the Scheme language or an extension. But you need Scheme to generate the code in the first place? It's a chicken-and-egg kind of thing. See call-with-continuation.org for a better explanation.


;;; -*- scheme-mode -*-
;;; Inline 'C' code with Chicken Scheme
(define inline-cube
  (foreign-lambda* int ((int num))
     "int result = (num * num * num);"
     "printf(\"inline cube of %d is \",num);"
     "return(result);"))
( print (inline-cube 13))
( display "goodbye\n" )
(exit)
;;
------------ console printout ------------
$ csc test2.scm
$ test2
inline cube of 13 is 2197
goodbye

Well, this example is somewhat un-Scheme-ly but I included Lambda to make it more so.

Let The Schemes Begin

2005-12-19T18:16:00.000-08:00

Scheme is inspired by the ancient programming language Lisp. There is a good overview on Wikipedia

Scheme/Lisp is interesting in part because it was inspired by Lambda Calculus, designed from a theory of computation, rather than to solve particular problems. Consequently, it is very general and without the constraints found in more commonly used languages.

This Blog chronicles my investigation of various Scheme implementations..