uCalc API Version: 5.7.0-preview.1 Released: 7/30/2026

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Project: Parsing and Evaluating Complex Boolean Logic

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A step-by-step guide to building a rule engine that can parse and evaluate complex boolean logic using uCalc's built-in operators and custom DSLs.

Remarks

🧠 Project: Parsing and Evaluating Complex Boolean Logic

This project demonstrates how to use uCalc to build a powerful engine for parsing and evaluating complex boolean logic expressions. This is a common requirement for applications like business rule engines, access control systems, search query parsers, and data validation frameworks.

The Goal: A Dynamic Rule Engine

We want to evaluate logical statements provided as strings at runtime, using a context of variables. Our engine should correctly handle:

  • Comparison Operators: ==, >, <, >=, <=, <>
  • Logical Operators: AND, OR, NOT
  • Grouping: Parentheses () to control the order of operations.

A typical expression might look like this:"(status == 'Active' AND login_attempts < 3) OR is_admin == true"

Why uCalc is the Perfect Tool

Building a boolean logic parser from scratch is a significant undertaking. You would need to implement a lexer, a parser that understands operator precedence (e.g., AND before OR), and an evaluation engine.

uCalc provides all of this functionality out of the box:

  • Built-in Operators: It already understands all standard comparison and logical operators.
  • Precedence & Associativity: The engine correctly handles the order of operations.
  • Dynamic Context: You can easily define variables at runtime to provide the data against which the rules are evaluated.
  • Extensibility: As shown in the practical example, you can use the ExpressionTransformer to create a more natural, domain-specific language (DSL) on top of the core logic.

Step 1: The Basic Approach (Using Built-in Logic)

The simplest way to evaluate a boolean expression is to define your variables and then pass the expression string directly to EvalStr(). uCalc's default grammar will handle the rest.

The "Succinct" example below demonstrates this direct approach.

Step 2: The Advanced Approach (Creating a Custom DSL)

For a more user-friendly or domain-specific syntax, you can use the ExpressionTransformer to transpile custom keywords into standard uCalc expressions before they are evaluated.

Let's say we want to support a more natural language syntax:

  • IS instead of ==
  • IS NOT instead of <>
  • CONTAINS for string searching

We can define simple FromTo rules to map this custom syntax to uCalc's built-in operators and functions. This creates a powerful abstraction layer, making the rules easier for non-programmers to write and understand.

The "Practical" example demonstrates this technique.

Step 3: Providing the Data Context

In either approach, the boolean expression is evaluated against a set of variables. These variables represent the "facts" or the current state of the system. You define them using DefineVariable() before evaluating the expression.

csharp
// Define the data context for our rule engine
uc.DefineVariable("status = 'Active'");
uc.DefineVariable("login_attempts = 2");
uc.DefineVariable("is_admin = false");

When the expression is evaluated, uCalc will look up these variable names and use their current values in the calculation.

Let's see the complete implementations.

Examples

Evaluates a complex boolean expression using uCalc's built-in operators.

ID: 1391

See: Project: Parsing and Evaluating Complex Boolean Logic 
				
					using uCalcSoftware;

var uc = new uCalc();
uc.DefineVariable("status = 'Active'");
uc.DefineVariable("login_attempts = 2");
uc.DefineVariable("is_admin = false");

var rule = "(status == 'Active' AND login_attempts < 3) OR is_admin == true";

Console.WriteLine($"Evaluating rule: {rule}");
Console.Write("Result: ");
Console.WriteLine(uc.EvalStr(rule));
				
			
Evaluating rule: (status == 'Active' AND login_attempts < 3) OR is_admin == true
Result: true
Explore 600+ other examples
				
					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

int main() {
   uCalc uc;
   uc.DefineVariable("status = 'Active'");
   uc.DefineVariable("login_attempts = 2");
   uc.DefineVariable("is_admin = false");

   auto rule = "(status == 'Active' AND login_attempts < 3) OR is_admin == true";

   cout << "Evaluating rule: " << rule << endl;
   cout << "Result: ";
   cout << uc.EvalStr(rule) << endl;
}
				
			
Evaluating rule: (status == 'Active' AND login_attempts < 3) OR is_admin == true
Result: true
Explore 600+ other examples
				
					Imports System
Imports uCalcSoftware
Public Module Program
   Public Sub Main()
      Dim uc As New uCalc()
      uc.DefineVariable("status = 'Active'")
      uc.DefineVariable("login_attempts = 2")
      uc.DefineVariable("is_admin = false")
      
      Dim rule = "(status == 'Active' AND login_attempts < 3) OR is_admin == true"
      
      Console.WriteLine($"Evaluating rule: {rule}")
      Console.Write("Result: ")
      Console.WriteLine(uc.EvalStr(rule))
   End Sub
End Module
				
			
Evaluating rule: (status == 'Active' AND login_attempts < 3) OR is_admin == true
Result: true
Explore 600+ other examples