 public func Filter(filter: (UInt, NSErrorPointer) -> MustacheBox?) -> FilterFunction {
     return { (box: MustacheBox, partialApplication: Bool, error: NSErrorPointer) in
         if partialApplication {
+            // This is a single-argument filter: we do not wait for another one.
             if error != nil {
                 error.memory = NSError(domain: GRMustacheErrorDomain, code: GRMustacheErrorCodeRenderingError, userInfo: [NSLocalizedDescriptionKey: "Too many arguments"])
             }

public func Filter(filter: (MustacheBox, NSErrorPointer) -> MustacheBox?) -> FilterFunction {
    return { (box: MustacheBox, partialApplication: Bool, error: NSErrorPointer) in
        if partialApplication {
            if error != nil {
                error.memory = NSError(domain: GRMustacheErrorDomain, code: GRMustacheErrorCodeRenderingError, userInfo: [NSLocalizedDescriptionKey: "Too many arguments"])
            }

public func Filter(filter: (Int?, NSErrorPointer) -> MustacheBox?) -> FilterFunction {
    return { (box: MustacheBox, partialApplication: Bool, error: NSErrorPointer) in
        if partialApplication {
            // This is a single-argument filter: we do not wait for another one.
            if error != nil {
                error.memory = NSError(domain: GRMustacheErrorDomain, code: GRMustacheErrorCodeRenderingError, userInfo: [NSLocalizedDescriptionKey: "Too many arguments"])
            }
