Digia Expressions

A powerful and flexible expression evaluator for Dart, designed to dynamically process expressions with support for variables, custom functions, and string interpolation. Built on an extensible visitor pattern architecture.

Note: This package is developed for internal use within Digia UI and is not intended for general public consumption.

Key Features

• Evaluate expressions: Mathematical, logical, and property access expressions
• Extensible Visitor Pattern: Create custom analyzers by extending Visitor<T>
• AST Access: Full access to the Abstract Syntax Tree for custom processing

Architecture

The library exposes its internals, allowing you to:

1. Parse expressions to AST using createAST()
2. Extend the Visitor pattern to create custom analyzers
3. Access all AST node types for complete control

Usage

Basic Expression Evaluation

import 'package:digia_expr/digia_expr.dart';

void main() {
  final context = BasicExprContext(variables: {
    'user': {'name': 'John Doe', 'age': 30}
  });
  
  final result = Expression.eval('user.name', context);
  print(result); // Output: John Doe
}

Extending the Visitor Pattern

Create custom visitors to analyze expressions:

import 'package:digia_expr/digia_expr.dart';

// Custom visitor to collect variable names
class VariableCollectorVisitor extends Visitor<List<String>> {
  @override
  List<String> visitProgram(ASTProgram node) {
    final List<String> vars = [];
    for (final expr in node.body) {
      // Implement traversal logic
    }
    return vars;
  }
  
  @override
  List<String> visitASTVariable(ASTVariable node) {
    return [node.name.lexeme];
  }
  
  // Implement other visit methods...
}

void main() {
  final ast = createAST('user.name') as ASTProgram;
  final collector = VariableCollectorVisitor();
  final variables = collector.visitProgram(ast);
  print(variables); // Output: [user]
}

Exported Components

When you import package:digia_expr/digia_expr.dart, you get access to:

• Visitor: Abstract base class for creating custom visitors
• AST Nodes: All AST node types (ASTProgram, ASTVariable, ASTGetExpr, etc.)
• createAST(): Parse expressions into AST
• Expression: Main evaluation class
• BasicExprContext: Basic context for expression evaluation
• StdLibFunctions: Standard library functions

Example Use Cases

1. Static Analysis: Analyze expressions to extract variable dependencies
2. Code Generation: Transform expressions into different formats
3. Validation: Check expressions before evaluation
4. Custom Evaluators: Build domain-specific expression evaluators
5. Dependency Tracking: Track what data an expression accesses

See example/digia_expr_example.dart for complete working examples.