https://github.com/appsup-dart/expressions

A library to parse and evaluate simple expressions.
https://github.com/appsup-dart/expressions

Last synced: 7 months ago
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A library to parse and evaluate simple expressions.

• Host: GitHub
• URL: https://github.com/appsup-dart/expressions
• Owner: appsup-dart
• License: bsd-3-clause
• Created: 2018-03-29T13:00:21.000Z (about 7 years ago)
• Default Branch: master
• Last Pushed: 2024-09-07T17:35:09.000Z (10 months ago)
• Last Synced: 2024-09-07T18:52:27.132Z (10 months ago)
• Language: Dart
• Size: 78.1 KB
• Stars: 41
• Watchers: 5
• Forks: 18
• Open Issues: 6
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • License: LICENSE

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# expressions

[![Build Status](https://travis-ci.org/appsup-dart/expressions.svg?branch=master)](https://travis-ci.org/appsup-dart/expressions)

A library to parse and evaluate simple expressions.

This library can handle simple expressions, but no operations, blocks of code, control flow statements and so on.

It supports a syntax that is common to most programming languages (so no special things like string interpolation, 

cascade notation, named parameters).

It is partly inspired by [jsep](http://jsep.from.so/).

## Usage

Example 1: evaluate expression with default evaluator

    // Parse expression:

    Expression expression = Expression.parse("cos(x)*cos(x)+sin(x)*sin(x)==1");

    // Create context containing all the variables and functions used in the expression

    var context = {

      "x": pi / 5,

      "cos": cos,

      "sin": sin

    };

    // Evaluate expression

    final evaluator = const ExpressionEvaluator();

    var r = evaluator.eval(expression, context);

    print(r); // = true

Example 2: evaluate expression with custom evaluator

    // Parse expression:

    Expression expression = Expression.parse("'Hello '+person.name");

    // Create context containing all the variables and functions used in the expression

    var context = {

      "person": new Person("Jane")

    };

    // The default evaluator can not handle member expressions like `person.name`.

    // When you want to use these kind of expressions, you'll need to create a

    // custom evaluator that implements the `evalMemberExpression` to get property

    // values of an object (e.g. with `dart:mirrors` or some other strategy).

    final evaluator = const MyEvaluator();

    var r = evaluator.eval(expression, context);

    print(r); // = 'Hello Jane'

## Features and bugs

Please file feature requests and bugs at the [issue tracker][tracker].

[tracker]: https://github.com/appsup-dart/expressions/issues

## Sponsor

Creating and maintaining this package takes a lot of time. If you like the result, please consider to [:heart: sponsor](https://github.com/sponsors/rbellens). 

With your support, I will be able to further improve and support this project.

Also, check out my other dart packages at [pub.dev](https://pub.dev/packages?q=publisher%3Aappsup.be).