A dart package to help you parse and evaluate infix mathematical expressions into their prefix and postfix notations.

Features

• Convert an infix expression into its prefix and postfix notations
• Evaluate a mathematical expression
• Support for basic mathematical operations

Usage

You can use infix-expression-parser as a library or as a CLI tool. Below are some examples explaining how to use the package in each case.

As a library

The package exposes two main classes:

• InfixExpressionConverter: Use this class when you have an infix expression and want to convert it either to its postfix or infix notation.
• ExpressionEvaluator: Use this class when you already have a postfix or prefix expression and want to evaluate it to a result. Use in combination with InfixExpressionConverter to also evaluate infix expressions easily. Note that in order to return a value, you need to provide a context in which you give each symbol in the expression a numeric value.

Example #1: Converting an infix expression

import 'package:infix_expression_parser/infix_expression_converter.dart';

void main() {
  // Provide an infix expression
  const infixExpression = '(a-b+c)*(d+e*f)';

  // Create an instance of InfixExpressionConverter
  final converter = InfixExpressionConverter(expression: infixExpression);

  final postfixExpression = converter.toPostfixNotation();
  final prefixExpression = converter.toPrefixNotation();

  print(postfixExpression); // ab-c+def*+*
  print(prefixExpression); // *+-abc+d*ef
}

Example #2: Evaluating a postfix expression

import 'package:infix_expression_parser/expression_evaluator.dart';

void main() {
  // Define a context map
  const context = {'a': 2, 'b': 3, 'c': 4, 'd': 5};

  // Provide a postfix expression
  const postfixExpression = 'abc+*d/';

  // Use the static method provided by the ExpressionEvaluator class and pass both the expression and the context
  final value = ExpressionEvaluator.evaluatePostfix(expression: postfixExpression, context: context);

  print(value); // 2.8
}

Example #3: Evaluating a prefix expression

import 'package:infix_expression_parser/expression_evaluator.dart';

void main() {
  // Define a context map
  const context = {'a': 2, 'b': 3, 'c': 4, 'd': 5, 'e': 6};

  // Provide a postfix expression
  const prefixExpression = '*-a/bc-/ade';

  // Use the static method provided by the ExpressionEvaluator class and pass both the expression and the context
  final value = ExpressionEvaluator.evaluatePrefix(expression: prefixExpression, context: context);

  print(value); // -7.0
}

Example #4: Evaluating an infix expression

import 'package:infix_expression_parser/infix_expression_converter.dart';
import 'package:infix_expression_parser/expression_evaluator.dart';

void main() {
  // Provide an infix expression
  const infixExpression = 'a-b+c-d*e';

  // Convert it to either its postfix or prefix notation
  final converter = InfixExpressionConverter(expression: infixExpression);
  final postfixExpression = converter.toPostfixNotation();

  // Define a context map
  const context = {'a': 2, 'b': 3, 'c': 4, 'd': 5, 'e': 6};

  // Use the static method provided by the ExpressionEvaluator class and pass both the expression and the context
  final value = ExpressionEvaluator.evaluatePostfix(expression: postfixExpression, context: context);

  print(value); // -27.0
}

As a CLI tool

The package expose a infix-parser command explained below:

A CLI tool for evaluating expressions in prefix or postfix notations or converting infix expressions.

Usage: infix-parser <command> [arguments]

Global options:
-h, --help    Print this usage information.

Available commands:
  convert   Converts an expression to its prefix or postfix notation

Run "infix-parser help <command>" for more information about a command.

You can use the convert sub-command to parse infix expressions.

Example #1: Converting an infix expression to a prefix expression

pub run infix_expression_parser:main convert '(a-b/c)*(a/d-e)'  --prefix
*-a/bc-/ade

Example #2: Converting an infix expression to a postfix expression

pub run infix_expression_parser:main convert '(a-b/c)*(a/d-e)'  --postfix
abc/-ad/e-*

Future improvements

• A sub-command for evaluating expressions in the command line may come in future iterations of this package
• Support for other mathematical operations, functions and symbols may come come in future iterations of this package