flutter_exprtk

ffi wrapper for exprtk math expression parser

See https://github.com/ArashPartow/exprtk for details

Limitations

Only works with doubles, not vectors etc.

Currently supports Android, MacOS, iOS, Web and Windows

To install

dependencies:
flutter:
    sdk: flutter

flutter_exprtk: ^0.0.9

Import the library:

import 'package:flutter_exprtk/flutter_exprtk.dart';

Web Platform:

Web is supported by a wasm module, injected at runtime and adds roughly 1.2MB to your app

Getting Started

// Create a new expression
final exp = Expression(
    expression: "a / b", // The expression
    variables: { "a": 4, "b": 2 }, // variables
    constants: {} // Optional constants can be omitted
);

// Get the value
print(exp.value); // -> 2

// Variables can be changed:
exp["a"] = 100
print(exp.value); // -> 50

exp["b"] = 50
print(exp.value); // -> 2

// Call clear to free up memory
expression.clear();

More complex example:

final exp2 = Expression(
    expression: "clamp(-1.0,sin(2 * pi * x) + cos(x / 2 * pi),+1.0)",
    variables: { "x": 0 }
);
for (double x = -5; x <= 5; x += 0.001)
{
    exp2["x"] = x;
    print("${exp2.value}");
}
// Call clear to free up memory
exp2.clear();

In a separate Isolate:

// Static or global function:
Future<List<double>> computeExpression (dynamic _) async {
    final exp2 = Expression(
        expression: "clamp(-1.0,sin(2 * pi * x) + cos(x / 2 * pi),+1.0)",
        variables: { "x": 0 }
    );
    final List<double> results = [];

    for (double x = -5; x <= 5; x += 0.001)
    {
        exp2["x"] = x;
        results.add(exp2.value);
    }
    exp2.clear();

    return results;
}

// Then run it for example with compute from flutter:foundation:
final results = await compute(computeExpression, null);
print("Results $results");

Handling errors

new Expression() will throw an "InvalidExpressionException" if the expression isn't valid.

A ClearedExpressionException will be thrown if an expression has been cleared.

If you try to set a variable which hasn't been initialized an "UninitializedVariableException" will be thrown:

try {
    final exp = Expression(
        expression: "///////", // will cause an InvalidExpressionException
        variables: {}
    );

    final exp = Expression(
        expression: "a + b",
        variables: { "c": 0 } // will cause an UninitializedVariableException
    );
    exp["d"] = 0; // will also cause an UninitializedVariableException

} on InvalidExpressionException {
    // ... handle exception
} on UninitializedVariableException {
    // ... handle exception
} on ClearedExpressionException {
    // ... handle exception
}

Libraries

flutter_exprtk

generated_plugin_registrant