OpenLanguage

OpenLanguage is a C# library providing lexers, parsers, and other processing tools for Open Office XML DSLs.

Features

WordprocessingML

• Field Instructions: Parse field instructions into strongly-typed Abstract Syntax Trees (AST)
• Grammar-Based: Uses GPLEX/GPPG for robust parsing of field instructions, expressions, and merge fields
• Comprehensive Field Types: Support for all field instructions - both standard ECMA variations and those specified in the ISO docs for legacy compatibility
• AST Manipulation: Programmatically access and modify parsed structures
• Field Reconstruction: Convert ASTs back to valid field instruction strings with round-trip fidelity

SpreadsheetML

• Formula Parsing: Parse SpreadsheetML formulas into Abstract Syntax Trees (AST)
• Grammar-Based: Uses GPLEX lexer (.lex) and GPPG yacc parser (.y) for concise and efficient grammar specification and parsing logic
• AST Manipulation: Access and modify parsed formula structures programmatically
• Formula Reconstruction: Convert modified ASTs back to valid Excel formula strings
• Reference Support: Handle A1, R1C1, table references, structured, and external references

Installation

Install via NuGet Package Manager:

dotnet add package OpenLanguage

Or via Package Manager Console:

Install-Package OpenLanguage

Quick Start

Formula Parsing

using OpenLanguage.SpreadsheetML.Formula;

// Parse an Excel formula
Ast.Node formula = FormulaParser.Parse("=SUM(A1:A10) * 2");

// Access the AST
Console.WriteLine($"Reconstructed: {formula.ToString()}");

// Try parsing with error handling
Ast.Node? maybeFormula = FormulaParser.TryParse("=INVALID_SYNTAX(");
if (maybeFormula == null)
{
    Console.WriteLine("Parse failed - invalid syntax");
}

Field Instruction Processing

using OpenLanguage.WordprocessingML.FieldInstruction;
using OpenLanguage.WordprocessingML.FieldInstruction.Ast;
using OpenLanguage.WordprocessingML.Ast;

// Parse a field instruction into a strongly-typed AST node
var ast = FieldInstructionParser.Parse("MERGEFIELD FirstName \\* Upper");

// Check the type and use specific properties
if (ast is MergeFieldFieldInstruction mergeField)
{
    Console.WriteLine($"Field Name: {mergeField.FieldName}");
    if (mergeField.GeneralFormat?.Argument is StringLiteralNode format)
    {
        Console.WriteLine($"General Format: {format.Value}");
    }
}

// Reconstruct field instruction
Console.WriteLine($"Field instruction: {ast.ToString()}");

Building from Source

Prerequisites

• .NET 8.0+ SDK
• CMake 3.20+ (for build system)
• cpp (C preprocessor for .y/.lex file processing)

Build Commands

The project uses a CMake-based build system with multiple targets:

# Configure build
cmake -B build

# Process .y/.lex files and generate code
cmake --build build --target process

# Build the solution
cmake --build build --target build

# Run tests
cmake --build build --target test

# Format code
cmake --build build --target format

# Generate documentation
cmake --build build --target doc

# Package for NuGet
cmake --build build --target pack

# Install git hooks
cmake --build build --target install-hooks

# Clean all build artifacts
cmake --build build --target clean-all

Alternative: Direct dotnet commands

# Restore dependencies
dotnet restore

# Build solution
dotnet build --configuration Release

# Run tests
dotnet test --configuration Release

# Format code
dotnet csharpier .

# Pack for NuGet
dotnet pack --configuration Release

Project Structure

OpenLanguage/
├── OpenLanguage/                  # Main library
│   ├── SpreadsheetML/
│   │   └── Formula/               # SpreadsheetML formula processing
│   │       ├── Lang/
│   │       │   ├── Lex/           # Lexical analysis (.lex files)
│   │       │   └── Parse/         # Grammar parsing (.y files)
│   │       └── FormulaParser.cs   # Main formula API and parser implementation
│   └── WordprocessingML/
│       ├── FieldInstruction/      # WordprocessingML field instructions
│       ├── MergeField/            # Mail merge functionality
│       └── Expression/            # Expression evaluation
├── OpenLanguage.Test/             # Unit tests
├── docs/                          # Documentation for docfx
├── docfx/                         # Docfx configuration
└── CMakeLists.txt                 # Build system configuration

Grammar Files

The project uses POSIX yacc/lex style grammar files for robust parsing:

• Formula Grammar: SpreadsheetML/Formula/Lang/Parse/formula.y
• Formula Lexer: SpreadsheetML/Formula/Lang/Lex/formula.lex
• Function Definitions: SpreadsheetML/Formula/Lang/Lex/function/*.lex

These files are processed during build to generate C# parser code.

Documentation

For detailed documentation, please visit the project documentation site.

The source for the documentation is in the docs/ and docfx/ directories.

Development

Code Style

This project uses CSharpier for code formatting:

# Format entire solution
dotnet csharpier format .

# Check formatting
dotnet csharpier check .

Git Hooks

Install git hooks to ensure code quality:

cmake --build build --target install-hooks

This installs a pre-commit hook that:

• Runs code formatting
• Executes all tests
• Prevents commits if tests fail

Testing

The project uses xUnit for testing:

# Run all tests
dotnet test

# Run tests with coverage
dotnet test --collect:"XPlat Code Coverage"

# Run specific test project
dotnet test OpenLanguage.Test/

Performance

OpenLanguage is built with performance as a primary concern:

• Native AOT Ready: Full compatibility with .NET Native AOT
• Optimized Grammar: LALR yacc parser used for SpreadsheetML formula parsing with highly optimized, minimal lex grammar. Compared against the ABNF grammar specification at each step of implementation.

Compatibility

• Multi-framework: Supports both .NET 8.0 and .NET 9.0
• Native AOT: Full support for ahead-of-time compilation

TODO

WordprocessingML

Field Instruction

Evaluation

• Implement per-class evaluation of strongly typed field instructions.
• Implement execution of parsed merge field.
• Ensure evaluation is implemented with respect to configured decimalSymbol

Misc

• Allow configuration option for decimalSymbol used for parsing floating point numbers
• Complete exhaustive enumeration of CountryRegion enumerations.

LevelText

• Define and implement paragraph numbering level text placeholder syntax grammar
• Implement AST parsing of paragraph numbering level text
• Implement placeholder value evaluator
• Add API for final, evaluated numbering level text construction

SpreadsheetML

Test coverage is quite comprehensive, as are grammar and parser rule specifications - there should not be anything left to complete here as far as implementation of parsing, parsing dependencies, nor AST. However, optimization leaves a bit to be desired, and evaluation is unimplemented.

Optimization

• Runtime memory consumption of FormulaParser and AST node classes, as well as size of generated parser code, jumped by ~10x on adding the builtin_function_call_head_raw rule. Investigate the cause and resolve.
• Many Shift, Reduce, Shift/Reduce, and Reduce/Reduce conflicts are automatically resolved on code generation of parser. Investigate the cause and resolve.

Evaluation

• Implement evaluation of formula, with a per-AST node class method called Evaluate, on the abstract ExpressionNode class and overriden by derived classes.
  • Implement all builtin SpreadsheetML functions.
  • Implement cell, sheet, table, and range reference resolution for read and write of underlying value.
  • Implement arithmetic expression evaluation.
  • Implement function reference resolution and call evaluation - regardless of whether user-defined, _xlpm.-prefixed function references, or LAMBDA functions.
• Bonus: implement a shared SpreadsheetContext to abstract common data reading and writing operations
  • Bonus if completed: in SpreadsheetContext, use generic underlying data representation which is derived from a common Spreadsheet class, allowing any underlying matrix-like data representation to be manipulated by formulas.

Example Usage

• Write a toy formula interpreter when evaluation is implemented.
  • Bonus: Realtime display and update of spreadsheet cell values in TUI with matrix display and formula input prompt as well as vim-style selection of corresponding cells. Simulaneously update underlying OPC package on modifying values.

PowerBI

• Define and implement grammar for Power Query
• Implement Power Query AST and parser

VBA

• Define and implement grammar for VBA Query
• Implement VBA Query AST and parser

Misc

Numbering Format

• Define and implement a numbering format grammar
• Implement numbering format AST representation
• Implement numbering format parser
• Implement numbering format applicator from AST class

See also

• ST_NumberFormat OOXML WML XSD Type
• Similar JS implementer specific to SML
• Another similar JS implementer specific to SML
• Standard format codes
• XSLT 1.0 Number Format Syntax. Very similar to SML's, seems to be identical to WML's except for possible differing defaults/keyword-based codes

Contributing

1. Fork the repository
2. Create a feature branch (git checkout -b feature/amazing-feature)
3. Make your changes
4. Ensure tests pass (cmake --build build --target test)
5. Ensure code is formatted (cmake --build build --target format)
6. Commit your changes (git commit -m 'Add amazing feature')
7. Push to the branch (git push origin feature/amazing-feature)
8. Open a Pull Request

License

This project is licensed under the GNU General Public License v2.0 - see the LICENSE file for details.

Acknowledgments

• Built with YaccLexTools for code generation from GPPG and GPLEX grammar specification and logic
• Uses DocumentFormat.OpenXml for Open Office XML handling

Support

• 📖 Documentation
• 🐛 Issue Tracker