Sprache

Sprache

Sprache is a simple, lightweight library for constructing parsers directly in C# code.

It doesn't compete with "industrial strength" language workbenches - it fits somewhere in between regular expressions and a full-featured toolset like ANTLR.

Usage

Unlike most parser-building frameworks, you use Sprache directly from your program code, and don't need to set up any build-time code generation tasks. Sprache itself is a single tiny assembly.

A simple parser might parse a sequence of characters:

// Parse any number of capital 'A's in a row
var parseA = Parse.Char('A').AtLeastOnce();

Sprache provides a number of built-in functions that can make bigger parsers from smaller ones, often callable via Linq query comprehensions:

Parser<string> identifier =
    from leading in Parse.WhiteSpace.Many()
    from first in Parse.Letter.Once().Text()
    from rest in Parse.LetterOrDigit.Many().Text()
    from trailing in Parse.WhiteSpace.Many()
    select first + rest;

var id = identifier.Parse(" abc123  ");

Assert.AreEqual("abc123", id);

Examples and Tutorials

The best place to start is this introductory article.

Examples included with the source demonstrate:

• Parsing XML directly to a Document object
• Parsing numeric expressions to System.Linq.Expression objects
• Parsing comma-separated values (CSV) into lists of strings

Tutorials explaining Sprache:

• Overview of Sprache methods, long guide by Justing Pealing
• A great CodeProject article by Alexey Yakovlev (and in Russian)
• Mike Hadlow's example of parsing connection strings
• Alexey Golub's article on monadic parser combinators that shows how to build a JSON parser using Sprache

Real-world parsers built with Sprache:

• The template parser in Octostache, the variable substitution language of Octopus Deploy
• The XAML binding expression parser in OmniXaml, the cross-platform XAML implementation
• Parts of the filter expression parser in Seq, a structured log server for .NET
• The connection string parser in EasyNetQ, a .NET API for RabbitMQ
• ApexSharp parser, a two-way Apex to C# transpiler (Salesforce programming language)
• Sprache appears in the credits for JetBrains ReSharper

Background

Parser combinators are covered extensively on the web. The original paper describing the monadic implementation by Graham Hutton and Eric Meijer is very readable. Sprache was originally written by Nicholas Blumhardt and grew out of some exercises in Hutton's Haskell book.

The implementation of Sprache draws on ideas from:

• Luke Hoban's Blog
• Brian McNamara's Blog