Candle Overview

Version	: Candle 0.10
Published date	: Nov 12, 2011

1. The Candle Language

Candle (Common ApplicatioN Development LanguagE) is designed to be a new general-purpose scripting language capable of developing both desktop and Internet applications.

Besides the common features found in many scripting languages, like cross-platform, interpreted execution, auto garbage collection, dynamic typed, built-in list and map support, Candle also supports some unique features that are not common in today's general-purpose programming languages:

Built-in hierarchical data processing: hierarchical data (whether from XML, HTML, XHTML, JSON, CSV, RDB or MIME Message) can be as easily constructed, selected (like XPath), queried (like XQuery), transformed (like XSLT) and serialized as any primitive data in Candle.
Set-oriented expressions: the expressions in Candle can handle not only a single item, but also a sequence of items - making the language more expressive and convenient.
Unified pattern language: Candle unifies several pattern related DSLs (including RegEx, BNF, RELAX NG, XQuery Sequence Type) into one consistent pattern language that can apply to sequence of items, nodes and string characters.
Unification of functional and procedural programming: Some multi-paradigm programming languages, like Python, already have a mixture of features from both worlds. But by introducing a mechanism, I called separation-of-side-effects, Candle unifies two worlds in a more orderly manner. In Candle, routines are divided into functions and methods. Functions are routines without side-effects and methods are routines with side-effects. The rule of separation-of-side-effects is that methods can call functions, but not vice versa. In this way, pure functional islands are well-preserved in the vast sea of procedural program.

Currently, the default character encoding (also the only supported encoding) of Candle is UTF8.

There are two types of documents in Candle - Candle Markup and Candle Script:

Candle Markup is for storing static markup data. It starts with opening signature <?cmk1.0?>. It is normally stored with file extension '.cmk'. The letters 'cmk' stands for Candle MarKup. Candle Markup is a strict subset of Candle script in syntax. And you can use 'text/x-candle' as the MIME type for Candle Markup.
Candle Script is for storing code. Its opening signature is <?csp1.0?>. It is normally stored with two file extensions '.csp' and '.run'. The letters 'csp' stands for Candle ScriPt. The former for general scripts and the latter for procedural main program. And you can use 'application/x-candle' as the MIME type for Candle Script.

In the opening signature, '1.0' is the version of the Candle language. As the language evolves, more version numbers would be expected to appear in the opening signature. Only whitespace characters are allowed to precede the opening signature.

As Candle is closely based on some XML technologies, including XPath, XSLT and XQuery, it will be easier for you to understand Candle, if you already have knowledge of these languages.

Two blog articles may also help you understand the design rationales behind Candle: Blog - Why I Invented Candle (I) and Blog - Why I Invented Candle (II).

2. The Candle App Platform

The Candle App Platform is the runtime environment to support the execution of Candle scripts on various operations systems. It is being developed in C/C++. Currently, Candle runs on Windows (2000 and above) and Linux (only tested with Ubuntu, but as Candle has very few dependencies, it should be easy to port to other Linux and UNIX distros).

Below is the architecture diagram of Candle App Platform:

Candle Runtime is very lightweight. With current beta release, the entire zipped binary package is only 2.1M on Windows and 1.2M on Linux. So besides running as standalone application, it can also be used as embedded scripting language in large applications.

The entire Candle Runtime implementation is open-sourced at SourceForge, so there's nothing that hinders you from porting it, customizing it and patching it. Workspace files for Microsoft Visual C++ (Express) and CodeLite are provided.

3. Candle Reference Documents

Here's a quick overview of the list of more detailed reference documents in Candle:

Candle Markup Reference: specifies the syntax and semantics for Candle markup document;
Candle Data Model Reference: specifies the type hierarchy and data model in Candle, which is essential to understanding the semantics of Candle script;
Candle Query Reference: specifies the scripting features in Candle;
Candle Pattern Reference: is dedicated to the pattern language in Candle, which can be used to specify patterns on sequence of items, nodes and strings.
Candle Routine Reference: documents the built-in routines in Candle;
Candle Style Reference: documents the style markup elements and attributes in Candle. This module is still being developed.
Candle Runtime Reference: documents the steps to install Candle, and run it in 3 slightly different ways, as a command line program, a desktop GUI program and a web application server.

If you encountered any problem with the program or the documentation, you can always email me at henryluo@candlescript.org
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