Implementation

Use Continuations to Develop Complex Web Applications

An introductory article from IBM developerWorks on Cocoon, continuation-based (sometimes called "modal") web applications, and such.

If you've ever developed a non-trivial Web application, you know that development complexity is increased by the fact that Web browsers allow users to follow arbitrary navigation paths through the application. No matter where the user navigates, the onus is on you, the developer, to keep track of the possible interactions and ensure that your application works correctly. While the traditional MVC approach does allow you to handle these cases, there are other options available to help resolve application complexity. Developer and frequent developerWorks contributor Abhijit Belapurkar walks you through a continuations-based alternative that could simplify your Web application development efforts.

via comp.lang.scheme

PyPy wins a funding contract with the EU

PyPy aims at producing a simple runtime-system for the Python language,

Our primary Scientific objective is to investigate novel techniques (based on Aspect-Oriented-Programming code generation and abstract interpretation) for the implementation of practical dynamic languages, breaking the compromise between flexibility, simplicity and performance trade-offs and expanding the range (small-to-large) of directly supportable runtime platforms.

CLR Generics and code sharing

I don't have the time at the moment to read it carefully, but this blog post looks promising.

Scheme on the CLR

Common Larceny (alpha release) is a CLI-targeted implementation of the Scheme programming language. The compiler generates MSIL and is interoperable with other .NET languages.
(spotter: Brad)

Skribe 1.2b released

(via comp.lang.scheme)

Erick Gallesio and Manuel Serrano have announced the release of version 1.2b of Skribe, a document processing language based on Scheme. From the home page:

Skribe is a text processor. Even [though] it is a general purpose tool, it best suits the writing of technical documents such as web pages or technical reports, API documentations, etc. At first glance, Skribe looks like a mark-up language à la HTML. So, there is no need to have developed computer programming skills to use Skribe.

A second look reveals that Skribe is actually a true programming language, provided with high level features (such as objects, higher order functions, regular and syntactic parsing, etc.). Skribe is based on the Scheme programming language.

From Skribe source files it is possible to produce various targets:

  • HTML pages that can be used to implement a web site (such as the Skribe Home Page).
  • XML files.
  • LaTeX files that can be used to produce high quality Postscript or PDF files.

What language enthusiast/researcher hasn't chafed at the language design of TeX? You should especially check out some of their cool examples.

Haskell Communities and Activities Report, Seventh Edition, November 2004

The November 2004 edition of the biannual Haskell Communities and Activities Report has been published. Lots of new stuff in the last six months, and some old stuff updated as well. The HC&AR has been steadily growing over the last three years, showing that FP is gaining users both professional and private.

Several of the HC&AR items are interesting enough to have their own LtU stories, which may appear shortly.

The Essential Haskell Compiler

On the same subject as the Scheme compiler in 90 Minutes, is the Essential Haskell Compiler. From the HC&AR summary:

The purpose of the EHC project is to provide a description a Haskell compiler which is as understandable as possible so it can be used for education as well as research


In order to avoid overwhelming the innocent reader, the description of the compiler is organised as a series of increasingly complex steps. Each step corresponds to a Haskell subset which itself is an extension of the previous step. The first step starts with the essentials, namely typed lambda calculus.



Sounds like BC Pierce's Types and Programming Languages.
Also notable is that EHC uses Utrecht's Attribute Grammars, which are interesting in their own right.

Rel: an open source implementation of Date & Darwen's Tutorial D

More from Slashdot, which today points to an article on Rel, Dave Voorhis' open source implementation of Tutorial D (see Chris Date and Hugh Darwen's The Third Manifesto for a discussion of the rationale behind this language).

Voorhis explains his motives for creating the implementation in an article on the (currently somewhat sparse) Rel Wiki.

Discussions of possible replacements of, or improvements on, SQL usually end up being all about the powerful institutional/human factors (or "network effects") that will impede acceptance of any new solution. Refreshingly, Voorhis is going ahead and building one anyway, without waiting for approval from the masses. It might catch on, or it might not; at least someone's giving it a go.

Generalized ADTs in Haskell

Simon Peyton-Jones, via Haskell-list:

I've finished my first attempt at implementing Generalised Algebraic
Data types in GHC. Ordinary algebraic data types are generalised to
allow you to write an explicit type signature for each constructor; for
example:

     data Term a where
	Lit :: Int -> Term Int
	Succ :: Term Int -> Term Int
	IsZero :: Term Int -> Term Bool	
	If :: Term Bool -> Term a -> Term a -> Term a

Notice that some of these constructors have return types that are not
just "Term a"... that's the whole point! Now you can write typed
evaluator for these terms:

    eval :: Term a -> a
    eval (Lit i)		= i
    eval (Succ t) 	= 1 + eval t
    eval (IsZero i) 	= eval i == 0
    eval (If b e1 e2)	= if eval b then eval e1 else eval e2

This is implementation of the "wobbly types" we've discussed before in GHC, slated for release in version 6.4. Simon also give a pointer to Tim Sheard's site, as he's done a lot of related work. There I found an interesting looking paper on Omega, a language which takes the GADT idea even further.

Smalltalk 80: Green Book

The text for Smalltalk-80, Bits of History, Words of Advice is now available online. The text documents the development history of the Smalltalk 80 language.

  • Part One of this book is a collection of papers that provide some
    background and history of the Smalltalk-80 implementation.
  • In Part Two we present papers that describe the experiences four
    implementors had in bringing their systems to life.
  • Part Three is a collection of measurements made by the
    implementation groups.
  • In Part Four we present papers that look toward the future of
    Smalltalk systems and propose ideas for extending the Smalltalk-80
    system beyond its initial form.

via Cincom Smalltalk Blogs.

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