evaluate method
Evaluates this expression according to given type and context.
Implementation
@override
dynamic evaluate(EvaluationType type, ContextModel context) {
final dynamic argEval = arg.evaluate(type, context);
if (type == EvaluationType.REAL) {
if (argEval < 0) return -1.0;
if (argEval == 0) return 0.0;
if (argEval > 0) return 1.0;
}
throw UnimplementedError('Can not evaluate $name on $type yet.');
}