Curl Language

CurlLanguage was developed originally MIT to provide a more consistent RichInternetApplication platform - without the discontinuities of HtmlDomJsCss + ajax + server-side scripting. Today, Curl is developed by Curl Inc. (, which provides a proprietary implementation and developer tools (payment is on developer side; the client-side runtime is free). The basic language is simply embedded in text by use of curly-brace delimiters {}, thus the name 'curl'. Default primitive display elements are inspired by HTML and TclTk, but also include data-grids and drill-down. Curl supports defining or extending OO classes, including the default ones.

Curl uses client-side JustInTimeCompilation to native code, which gives enough performance for rich 2D, 3D, sound, visualizing and manipulation of large data sets - enough to make it suitable basis for a gaming client or browser or IDE. (Indeed, Curl's main IDE is implemented in Curl.) Security is achieved through a combination of StrongTyping and sandboxing. Typing is not static; similar to Ruby or Smalltalk, types are objects that can be patched or mutated at runtime.

A few features supported by the Curl language design but not by most competing technologies: Curl's primary LanguageDesign goal was a 'gentle slope' for developers. This includes both minimizing discontinuity between client-side and server-side, and providing a 'gentle slope' between generating simple formatted text and RichInternetApplications - i.e. to avoid huge leaps in the required language skills, translation challenges, or knowledge of security and optimization issues for client-side vs. server-side elements.

The Curl web programming environment is a proprietary Rich Client (or sometimes called a "fit" client) designed to offload most processing from the server. The client consists of a JustInTimeCompiler, a multimedia engine, a UI framework, and XML parsers and networking libraries for communication. It receives source code via HTTP and compiles and executes it on-the-fly, using normal sandboxing techniques for security. Preprocessed Curl source code (Pcurl files) is quite compact (see CurlLanguageExamples), leading to very quick downloads and can be either selectively cached or dynamically loaded.

Some of the strengths of Curl come from its having a combination of multiple inheritance, factory methods, macros and having anonymous functions that are first-class objects as well as the runtime JIT compiler compiling Curl to native code.

Curl code is also homoiconic: Curl can be both the code and the data format.

Curl is first and foremost a web-content language intended to replace or complement both HTML+JavaScript and XHTML.

Curl has had async processing since at least 2001 (long before AJAX was a buzzword).

Curl is now at version 7.0 and since 6.0 has had a separation of style from content as well as interfaces to JavaScript and JSON. Recently Curl add support for SQLite including as a in-memory db.

Curl's permission for abstract classes to implement some methods and use of multiple inheritance constitutes a Mixin strategy roughly equivalent to Traits (but as of 2009/07 Curl still lacks a RefactoringBrowser or even full class browsers.

One Curl asset is the "live" code contained in the Curl documentation which is itself Curl code. Using the {example} macro, the reader can edit code, execute code, save code and reset code.

After years in Smalltalk environments, a developer working in Curl has rated it a close "second best" due to its able debugger and graphical inspection tools.

Curl offers two programming styles: declarative and procedural (which can be quite freely mixed and, with macros, modified).

Curl permits prototyping with no types other than the "any" type and then progressively adding constraints in the form of compiler directives to achieve production or industrial-strength code.

Since 2007, Curl has been releasing add-on packages as opensource (Curl Inc. was an MIT spinoff and is now owned by Sumisho).

As of 2009 Curl is primarily used in Japan but has global use in governments and large corporations due to the widespread use of the GRC suite of Paisley Consulting (acquired in Dec 2008 by Thomson Reuters).

As is the case with JavaScript, Curl has spawned such commercial add-ins as custom spreadsheets.

Although has no curl version of its web site, but (which used to focus only on Smalltalk + PROLOG) now has Curl pages that run most of the available Curl demos: installation of the Curl runtime is required to view those Curl pages.

Prior to Curl 7.0, processes (sub-applets) and Curl scripts (xcurl files) went largely undocumented. Files with the extension "dcurl" are now used to install Curl applets as desktop applications. Curl 7.0 includes splash screens built with Curl's IPC (inter-process communication) API.

Curl packages now offer digital signing as an option.

See (info) (developers) or (in Japanese).

Question: Why should one use this proprietary language over other established proprietary GUI languages such as Adobe's Flex/ActionScript?

The continuity issue would be the biggest advantage. With Adobe's Flex/ActionScript, you'll do a lot of rework tweaking what executes client-side versus what executes server-side. (And it will involve rework, because you'll be using different languages and different projects for server-side vs. client-side.) You'll spend time learning several different languages, and you'll write extra code to interface them. By designing away a few DiscontinuitySpikes, plus providing some good default libraries, Curl app code tends to be smaller than Ajax or Flex. (OTOH, the Curl RTE plugin is bigger.) By supporting homoiconic code, extensible types, and sandboxing and JIT, Curl apps can be extended with minimal changes to existing code.

Curl Inc. would also emphasize their offline support, which comes from a good choice of default library design than from the CurlLanguage proper. But you can peruse if you want to know what Curl Inc. thinks.

For rich multi-media, you should currently favor Adobe's product. Curl is targeted more towards BusinessApplications? (business-to-employee and business-to-business) involving large dataset processing and visualization (reports, graphs, dashboards, heatmaps, datagrids, etc.). There is no reason video couldn't be supported, but it hasn't received much demand from the businesses using Curl.

I find Curl interesting because it is, in fact, a language with a consistent LanguageDesign behind it, as opposed to a hodge-podge of frameworks and inconsistent mini-languages like Adobe. There is a lot more to learn from Curl than from most of its competition.

Personally, I wouldn't use either of them. Curl's developer license for shared apps has a $12k price tag (though it's free for personal use). I'm also more interested in InteractiveDocuments than in RichInternetApplications, and sandbox-based security is not sufficiently expressive for many of the design patterns that I'd like to support (cf. ObjectCapabilityModel, PowerBox). But, even if my goal is to develop a competing platform aligned with my own interests, I should learn my competition and be inspired by their better ideas.


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