void main() {
  Expression exp = Expression("2 ^ 4 + 8");
  print(exp.eval().toString()); // 24

  // With a variable
  exp = Expression("a ^ b + c");
  // Variables may contain alphanumeric characters, and "_". This can be changed
  // by using setVariableCharacters(..) and setFirstVariableCharacters(..) (what chars variable are allowed to start with).
  exp.setStringVariable("a", "2");
  exp.setStringVariable("b", "4");
  exp.setStringVariable("c", "8");
  print(exp.eval().toString()); // 24
  
  // With a function
  exp = Expression("MAX(-7,8)");
  print(exp.eval().toString()); // 8

  // Boolean logic
  exp = Expression("1>0 && 5 == 5");
  print(exp.eval().toString()); // 1
  
  exp = Expression("1>0 && 5 == 4");
  print(exp.eval().toString()); // 0

  // Adding a custom operator

  Expression exp = Expression('23 custom_operator 20');
  exp.addOperator(OperatorImpl("custom_operator", Expression.operatorPrecedenceAdditive, true,
      fEval: (v1, v2) {
    return v1 + v2;
  }));
  print(exp.eval()); // 43

  // Adding a custom function

  exp = Expression('cube(4) + 2');
  exp.addFunc(FunctionImpl("cube", 1, booleanFunction: false, fEval: (params) {
   num n = pow(params.first.toDouble(),3);
   return Decimal.parse(n.toString());
  }));
  print(exp.eval()) // 66

  // Custom function for returning the difference between two numbers

  exp = Expression('difference(4,2)');
  exp.addFunc(FunctionImpl("difference", 2, booleanFunction: false, fEval: (params) {
   return (params[0]-params[1]).abs();
  }));
  print(exp.eval()); // 2
}