Snowflake lets you interactively create PEG-based recursive-descent parsers via a GUI.

Quick Links:

• Grammar Cheat Sheet
• JavaDoc
• Code Coverage

Maven Dependency:

<dependency>
    <groupId>com.mackenziehigh</groupId>
    <artifactId>snowflake</artifactId>
    <version>2.0</version>
</dependency>

Hello World

Step: Download GUI from Maven Central:

Click Here to download the ready-to-run Snowflake JAR file.

Step: Run the GUI

java -cp snowflake-2.0.jar com.mackenziehigh.snowflake.designer.gui.MainWindow

The following window will appear on screen.

Step: Download the Demonstration Grammar:

Click Here to download the planet-demo.snow file.

Step: Open the Demonstation Grammar:

• Click File -> Open Project
• Select the planet-demo.snow file that you just downloaded in the previous step.

The GUI will be populated with the grammar and example from the planet-demo.snow file.

The example input is displayed on the Input tab of the GUI.

Step: Parse the Example Input:

Click Action -> Parse on the GUI.

The grammar will be used to parse the example input and then the resulting parse tree will be displayed.

The nodes in the tree correspond to the matching grammar rules.

Click on nodes to see the portion of text corresponding to that node.

Introduction to Parsing using PEGs

Here is a powerpoint presentation that will introduce you to parsing using Parsing Expression Grammars.

Example Projects

These projects include executable example programs that utilize Snowflake for parsing.

• Simple Phone Book
• Prefix Notation Calculator
• Infix Notation Calculator

External Resources

• Wikipedia: Parsing Expression Grammars
• The Packrat Parsing and Parsing Expression Grammars Page
• The Grammar of Snowflake Grammars