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.
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'
Please file feature requests and bugs at the issue tracker.
Creating and maintaining this package takes a lot of time. If you like the result, please consider to ❤️ sponsor. With your support, I will be able to further improve and support this project. Also, check out my other dart packages at pub.dev.
