Server-side validation code for Mkay.

MkayAttribute.IsValid.cs

protected override ValidationResult IsValid(object value, ValidationContext validationContext)
{
  var subject = validationContext.ObjectInstance;
  var memName = validationContext.MemberName;
  if (memName == null)
  {
    throw new Exception(
      "Property name is not set for property with display name " + validationContext.DisplayName
      + ", you should register the MkayValidator with the MkayAttribute in global.asax.");
  }

  var validator = CreateValidator(subject, memName, Tree);

  return validator() 
    ? ValidationResult.Success 
    : new ValidationResult(ErrorMessage ?? _defaultErrorMessage);
}

private static Func<bool> CreateValidator(object subject, string property, ConsCell ast)
{
  var builder = new ExpressionTreeBuilder(subject, property);
  var viz = new ExpVisitor<Expression>(builder);
  ast.Accept(viz);
  var exp = viz.GetResult();
  var validator = builder.DeriveFunc(exp).Compile();
  return validator;
}