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haxpression

Basic math expression parser and evaluator for Haxe

Description

This library parses basic math expressions into an expression-tree, and provides methods to replace variables with values or other expressions, simplify expressios, and evaluate expressions.

Credits

The expression parser logic was ported from this JavaScript library: jsep.

Examples

Basic expression parsing and evaluation

// parse an expression string into an expression tree (Expression)
var expr = Parser.parse('1 + x / y');

// same as:
var expr : Expression = '1 + x / y';

trace(expr);
// prints: (1 + (x / y))

trace(expr.toObject());
// prints:
// {
//   "type": "Binary",
//   "operator": "+",
//   "left: {
//     type: "Literal",
//     value: 1
//   },
//   "right": {
//     "type": "Binary",
//     "operator": "/",
//     "left": {
//       "type": "Identifier",
//       "name": "x"
//     },
//     "right": {
//       "type": "Identifier",
//       "name": "y"
//     }
//   }
// }

trace(expr.getVariables());
// prints: ["x", "y"]

// evaluate with variable values:
var result : Float = expr.evaluate([
  "x" => 5,
  "y" => 10
]);

trace(result);
// prints 1.5

Expression group parsing and evaluation

An "expression group" consists of a set of named expressions, which can consist of variables defined both internally and externally to the group. The group can be evaluated by providing all of the external variable values, and by resolving the interal variable references. There cannot be any circular references between variables/expressions.

var group = new ExpressionGroup([
  'MAP_1' => '2 * SOURCE_1 + 3 * SOURCE_2', // external variables
  'MAP_2' => '0.5 * SOURCE_1 + 10 * MAP_1', // external and internal variables
  'MAP_3' => '0.2 * MAP_1 + 0.3 * MAP_2', // internal variables
]);

var result = group.evaluate([
  'SOURCE_1' => 2.34,
  'SOURCE_2' => 3.14
]);

trace(result);
// prints:
// {
//   MAP_1 => 14.1,
//   MAP_2 => 142.17,
//   MAP_3 => 45.471,
//   SOURCE_1 => 2.34,
//   SOURCE_2 => 3.14,
// }

Customizable binary/unary/function operations

haxpression provides default binary, unary, and function operations out-of-the-box, including most of the common math operators and Math functions.

Binary, unary, and function call operations can be customized using the BinaryOperations, UnaryOperations, and CallOperations classes.

// Use built-in + binary operator and abs function
var result : Int = ('1 + abs(x)' : Expression).evaluate([ "x" => -5 ]);
trace(result);
// prints: 6

// Create new binary operator and function
CallOperations.add("myfunc", 2, function(arguments) return arguments[0].toFloat() + arguments[1].toFloat()); // 2 is the function arity
BinaryOperations.add("&&&", 10, function(left, right) return left.toFloat() / right.toFloat()); // 10 is the operator precedence - see BinaryOperations

var resultFloat : Float = ('myfunc(x, 10) &&& myfunc(y, 20)' : Expression).evaluate([ "x" => 2, "y" => 3 ]);
trace(resultFloat);
// prints: 0.5217391304347826 = (2 + 10) / (3 + 20)