Curl (programming language)

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File:Curl logo.gif
Paradigm multi-paradigm: object-oriented, markup
Appeared in 1998
Designed by Steve Ward, MIT
Developer Curl, Inc. & Sumisho Computer Systems Corp.
Stable release 7.0.0
Typing discipline strong
Influenced by HTML, JavaScript
OS Cross-platform: Windows, Linux, Macintosh

Curl is a reflective object-oriented programming language for interactive web applications whose goal is to provide a smoother transition from between formatting and programming; providing a means to embed more complex objects in simple documents without having to switch between programming languages or development platforms.

The language attempts to address a long-standing problem: the different building blocks that make up any modern web document most often require wildly different methods of implementation: different languages, different tools, different frameworks, often completely different teams. The final—and often most difficult— hurdle has been getting all of these blocks to communicate with each other in a consistent manner. Curl attempts to side-step these problems by providing a consistent syntactical and semantic interface at all levels of web content creation: from simple HTML to complex object-oriented programming.

Curl combines text markup (as in HTML), scripting (as in JavaScript), and heavy-duty computing (as in Java, C#, or C++) within one unified framework. It is used in a range of internal enterprise, B2B, and B2C applications.

Curl is a markup language like HTML—that is, plain text is shown as text; at the same time, Curl includes an object-oriented programming language that supports multiple inheritance. Curl applications are not required to observe the separation of information, style, and behavior that HTML, CSS, and JavaScript have imposed, although that style of programming can be used in Curl if desired.

While the Curl language can be used as an HTML replacement for presenting formatted text, its capabilities range all the way to those of a compiled, strongly typed, object-oriented system programming language.[1] Both the authoring (HTML-level) and programming constructs of Curl can be extended in user code. The language is designed so Curl applications can be compiled to native code of the client machine by a just-in-time compiler and run at high speed.

Curl applets are viewed using the Curl RTE, a runtime environment with a plugin for web browsers. Currently, it is supported on Microsoft Windows, Linux, and Macintosh.

Curl has had a feature of "detached applets" for several years, which is a web deployed applet which run on the user's desktop independent of a browser window much as in Silverlight 3 and Adobe AIR. Curl applets can also be written so that they will run off-line when disconnected from the network (occasionally-connected computing). In fact, the Curl IDE is an application written in Curl.



A simple Curl applet for HelloWorld might be

{Curl 5.0, 6.0, 7.0 applet}
   color = "blue",
   font-size = 16pt,
   Hello World}

This code will run if the user has at least one of the Curl versions 5.0, 6.0, or 7.0 installed.

Curl provides both macros and text-procedures in addition to anonymous procedures and named methods. An alternative using the text-procedure paragraph would be:

   {text color = "red", font-size = 12pt,
   {text color = "green", font-size = 12pt,

Recently this style of layout has been adopted by 'builders' in the Groovy language for the JVM, but is also familiar to users of CSS or Tcl/Tk. Most features for RIA now sought through combinations of JavaScript libraries + HTML + CSS are already found within the Curl language including features usually associated with Prototype + Scriptaculous such as accordion panes.

Curl sets callbacks in the manner also adopted by Groovy:

{CommandButton width=100pt,
   height = 50pt,
   label = {center {bold Invokes an event handler when clicked}},
   control-color = "orange",
   || Attach the following event handler to this CommandButton
   {on Action do
           title = "Your Message",
           "This is a user message dialog."

Curl comments use the vertical bar in several variations. The simplest is as follows:

{text A comment can be on a line by itself,
|| A comment on a line by itself
or it can be at the end || A comment on the same line as code
of a line.}


Curl, Inc. is headquartered in Cambridge, Massachusetts and is a wholly owned a subsidiary of Sumisho Computer Systems Corp.. The largest number of over 400 commercial Curl customers are currently in Japan and other Asian countries, but Curl is also available in the Western world.

Curl is free to use for non-commercial and some commercial uses (see licensing). A Pro version is available which provides additional enterprise class capabilities.

See also

  • Homoiconicity: Curl is both a programming language and a data format



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