Deno Equation Parser

A robust mathematical equation parser for Deno that supports arithmetic operations, variables, parentheses, and proper error handling.

Features

• Basic arithmetic operations (+, -, *, /, ^)
• Support for parentheses and nested expressions
• Variable substitution
• Unary operators (positive and negative numbers)
• Scientific notation
• Comprehensive error handling
• Zero dependencies

Installation

import { evaluateExpression } from "jsr:@blake-to/equation-parser";

Quick Start

// Basic arithmetic
console.log(evaluateExpression("2 + 3 * 4"));  // 14
console.log(evaluateExpression("(2 + 3) * 4")); // 20
console.log(evaluateExpression("-5 * -3"));     // 15

// With variables
const variables = new Map([
    ["x", 5],
    ["y", 3]
]);
console.log(evaluateExpression("x + y", variables));     // 8
console.log(evaluateExpression("2 * x + y", variables)); // 13

API Reference

Main Function

evaluateExpression(expression: string, variables?: Map<string, number>): number

Evaluates a mathematical expression and returns the result.

Parameters:

• expression: string - The mathematical expression to evaluate.
• variables?: Map<string, number> - Optional map of variable names to their values.

Returns:

• number - The result of evaluating the expression.

Throws:

• InvalidSyntaxError - When the expression contains invalid syntax.
• UndefinedVariableError - When a variable is used but not defined.
• DivisionByZeroError - When attempting to divide by zero.

Error Classes

InvalidSyntaxError: Thrown when the expression contains invalid syntax.

try {
    evaluateExpression("2 + + 3");
} catch (error) {
    if (error instanceof InvalidSyntaxError) {
        console.error(error.message); // "Consecutive operators are not allowed"
    }
}

UndefinedVariableError: Thrown when a variable is used but not defined in the variables map.

try {
    evaluateExpression("x + 5");
} catch (error) {
    if (error instanceof UndefinedVariableError) {
        console.error(error.message); // "Undefined variable: x"
    }
}

DivisionByZeroError: Thrown when attempting to divide by zero.

try {
    evaluateExpression("5 / 0");
} catch (error) {
    if (error instanceof DivisionByZeroError) {
        console.error(error.message); // "Division by zero"
    }
}

Supported Operations

Arithmetic Operators

• Addition: +
• Subtraction: -
• Multiplication: *
• Division: /
• Exponentiation: ^

Unary Operators

• Positive: +
• Negative: -

Parentheses

• Grouping: ( and )

Numbers

• Integers: 42
• Decimals: 3.14
• Scientific Notation: 1e-10, 1.5e+3

Variables

• Must start with a letter or underscore.
• Can contain letters, numbers, and underscores.
• Case-sensitive.

Examples

Basic Arithmetic

evaluateExpression("2 + 3")          // 5
evaluateExpression("2 * 3")          // 6
evaluateExpression("10 - 4")         // 6
evaluateExpression("12 / 3")         // 4
evaluateExpression("2 ^ 3")          // 8

Complex Expressions

evaluateExpression("2 + 3 * 4")              // 14
evaluateExpression("(2 + 3) * 4")            // 20
evaluateExpression("2 * (3 + 4)")            // 14
evaluateExpression("((2 + 3) * (4 + 5))")    // 45

Variables

const variables = new Map([
    ["x", 5],
    ["y", 3],
    ["price", 9.99]
]);

evaluateExpression("x + y", variables)         // 8
evaluateExpression("x * y", variables)         // 15
evaluateExpression("price * 2", variables)     // 19.98

Scientific Notation

evaluateExpression("1e3")        // 1000
evaluateExpression("1.5e-2")     // 0.015
evaluateExpression("1.5e+3")     // 1500

Error Handling

// Invalid syntax
try {
    evaluateExpression("2 + + 3");
} catch (error) {
    console.error(error.message); // "Consecutive operators are not allowed"
}

// Undefined variable
try {
    evaluateExpression("x + 5");
} catch (error) {
    console.error(error.message); // "Undefined variable: x"
}

// Division by zero
try {
    evaluateExpression("5 / 0");
} catch (error) {
    console.error(error.message); // "Division by zero"
}

Testing

Run the test suite:

deno test

Contributing

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add some amazing feature)
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

License

This project is licensed under the MIT License (see the LICENSE file for details)

Version History

• 1.0.0
  • Initial release
  • Basic arithmetic operations
  • Variable support
  • Error handling
  • Parentheses support
  • Scientific notation support